assignment instruction java

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• 1.1 Preface
• 1.2 Why Programming? Why Java?
• 1.3 Variables and Data Types
• 1.4 Expressions and Assignment Statements
• 1.5 Compound Assignment Operators
• 1.6 Casting and Ranges of Variables
• 1.7 Java Development Environments (optional)
• 1.8 Unit 1 Summary
• 1.9 Unit 1 Mixed Up Code Practice
• 1.10 Unit 1 Coding Practice
• 1.11 Multiple Choice Exercises
• 1.12 Lesson Workspace
• 1.3. Variables and Data Types" data-toggle="tooltip">
• 1.5. Compound Assignment Operators' data-toggle="tooltip" >

1.4. Expressions and Assignment Statements ¶

In this lesson, you will learn about assignment statements and expressions that contain math operators and variables.

1.4.1. Assignment Statements ¶

Remember that a variable holds a value that can change or vary. Assignment statements initialize or change the value stored in a variable using the assignment operator = . An assignment statement always has a single variable on the left hand side of the = sign. The value of the expression on the right hand side of the = sign (which can contain math operators and other variables) is copied into the memory location of the variable on the left hand side.

Figure 1: Assignment Statement (variable = expression) ¶

Instead of saying equals for the = operator in an assignment statement, say “gets” or “is assigned” to remember that the variable on the left hand side gets or is assigned the value on the right. In the figure above, score is assigned the value of 10 times points (which is another variable) plus 5.

The following video by Dr. Colleen Lewis shows how variables can change values in memory using assignment statements.

As we saw in the video, we can set one variable to a copy of the value of another variable like y = x;. This won’t change the value of the variable that you are copying from.

Click on the Show CodeLens button to step through the code and see how the values of the variables change.

The program is supposed to figure out the total money value given the number of dimes, quarters and nickels. There is an error in the calculation of the total. Fix the error to compute the correct amount.

Calculate and print the total pay given the weekly salary and the number of weeks worked. Use string concatenation with the totalPay variable to produce the output Total Pay = $3000 . Don’t hardcode the number 3000 in your print statement.

Assume you have a package with a given height 3 inches and width 5 inches. If the package is rotated 90 degrees, you should swap the values for the height and width. The code below makes an attempt to swap the values stored in two variables h and w, which represent height and width. Variable h should end up with w’s initial value of 5 and w should get h’s initial value of 3. Unfortunately this code has an error and does not work. Use the CodeLens to step through the code to understand why it fails to swap the values in h and w.

1-4-7: Explain in your own words why the ErrorSwap program code does not swap the values stored in h and w.

Swapping two variables requires a third variable. Before assigning h = w , you need to store the original value of h in the temporary variable. In the mixed up programs below, drag the blocks to the right to put them in the right order.

The following has the correct code that uses a third variable named “temp” to swap the values in h and w.

The code is mixed up and contains one extra block which is not needed in a correct solution. Drag the needed blocks from the left into the correct order on the right, then check your solution. You will be told if any of the blocks are in the wrong order or if you need to remove one or more blocks.

After three incorrect attempts you will be able to use the Help Me button to make the problem easier.

Fix the code below to perform a correct swap of h and w. You need to add a new variable named temp to use for the swap.

1.4.2. Incrementing the value of a variable ¶

If you use a variable to keep score you would probably increment it (add one to the current value) whenever score should go up. You can do this by setting the variable to the current value of the variable plus one (score = score + 1) as shown below. The formula looks a little crazy in math class, but it makes sense in coding because the variable on the left is set to the value of the arithmetic expression on the right. So, the score variable is set to the previous value of score + 1.

Click on the Show CodeLens button to step through the code and see how the score value changes.

1-4-11: What is the value of b after the following code executes?

• It sets the value for the variable on the left to the value from evaluating the right side. What is 5 * 2?
• Correct. 5 * 2 is 10.

1-4-12: What are the values of x, y, and z after the following code executes?

• x = 0, y = 1, z = 2
• These are the initial values in the variable, but the values are changed.
• x = 1, y = 2, z = 3
• x changes to y's initial value, y's value is doubled, and z is set to 3
• x = 2, y = 2, z = 3
• Remember that the equal sign doesn't mean that the two sides are equal. It sets the value for the variable on the left to the value from evaluating the right side.
• x = 1, y = 0, z = 3

1.4.3. Operators ¶

Java uses the standard mathematical operators for addition ( + ), subtraction ( - ), multiplication ( * ), and division ( / ). Arithmetic expressions can be of type int or double. An arithmetic operation that uses two int values will evaluate to an int value. An arithmetic operation that uses at least one double value will evaluate to a double value. (You may have noticed that + was also used to put text together in the input program above – more on this when we talk about strings.)

Java uses the operator == to test if the value on the left is equal to the value on the right and != to test if two items are not equal. Don’t get one equal sign = confused with two equal signs == ! They mean different things in Java. One equal sign is used to assign a value to a variable. Two equal signs are used to test a variable to see if it is a certain value and that returns true or false as you’ll see below. Use == and != only with int values and not doubles because double values are an approximation and 3.3333 will not equal 3.3334 even though they are very close.

Run the code below to see all the operators in action. Do all of those operators do what you expected? What about 2 / 3 ? Isn’t surprising that it prints 0 ? See the note below.

When Java sees you doing integer division (or any operation with integers) it assumes you want an integer result so it throws away anything after the decimal point in the answer, essentially rounding down the answer to a whole number. If you need a double answer, you should make at least one of the values in the expression a double like 2.0.

With division, another thing to watch out for is dividing by 0. An attempt to divide an integer by zero will result in an ArithmeticException error message. Try it in one of the active code windows above.

Operators can be used to create compound expressions with more than one operator. You can either use a literal value which is a fixed value like 2, or variables in them. When compound expressions are evaluated, operator precedence rules are used, so that *, /, and % are done before + and -. However, anything in parentheses is done first. It doesn’t hurt to put in extra parentheses if you are unsure as to what will be done first.

In the example below, try to guess what it will print out and then run it to see if you are right. Remember to consider operator precedence .

1-4-15: Consider the following code segment. Be careful about integer division.

What is printed when the code segment is executed?

• 0.666666666666667
• Don't forget that division and multiplication will be done first due to operator precedence.
• Yes, this is equivalent to (5 + ((a/b)*c) - 1).
• Don't forget that division and multiplication will be done first due to operator precedence, and that an int/int gives an int result where it is rounded down to the nearest int.

1-4-16: Consider the following code segment.

What is the value of the expression?

• Dividing an integer by an integer results in an integer
• Correct. Dividing an integer by an integer results in an integer
• The value 5.5 will be rounded down to 5

1-4-17: Consider the following code segment.

• Correct. Dividing a double by an integer results in a double
• Dividing a double by an integer results in a double

1-4-18: Consider the following code segment.

• Correct. Dividing an integer by an double results in a double
• Dividing an integer by an double results in a double

1.4.4. The Modulo Operator ¶

The percent sign operator ( % ) is the mod (modulo) or remainder operator. The mod operator ( x % y ) returns the remainder after you divide x (first number) by y (second number) so 5 % 2 will return 1 since 2 goes into 5 two times with a remainder of 1. Remember long division when you had to specify how many times one number went into another evenly and the remainder? That remainder is what is returned by the modulo operator.

Figure 2: Long division showing the whole number result and the remainder ¶

In the example below, try to guess what it will print out and then run it to see if you are right.

The result of x % y when x is smaller than y is always x . The value y can’t go into x at all (goes in 0 times), since x is smaller than y , so the result is just x . So if you see 2 % 3 the result is 2 .

1-4-21: What is the result of 158 % 10?

• This would be the result of 158 divided by 10. modulo gives you the remainder.
• modulo gives you the remainder after the division.
• When you divide 158 by 10 you get a remainder of 8.

1-4-22: What is the result of 3 % 8?

• 8 goes into 3 no times so the remainder is 3. The remainder of a smaller number divided by a larger number is always the smaller number!
• This would be the remainder if the question was 8 % 3 but here we are asking for the reminder after we divide 3 by 8.
• What is the remainder after you divide 3 by 8?

1.4.5. FlowCharting ¶

Assume you have 16 pieces of pizza and 5 people. If everyone gets the same number of slices, how many slices does each person get? Are there any leftover pieces?

In industry, a flowchart is used to describe a process through symbols and text. A flowchart usually does not show variable declarations, but it can show assignment statements (drawn as rectangle) and output statements (drawn as rhomboid).

The flowchart in figure 3 shows a process to compute the fair distribution of pizza slices among a number of people. The process relies on integer division to determine slices per person, and the mod operator to determine remaining slices.

Figure 3: Example Flow Chart ¶

A flowchart shows pseudo-code, which is like Java but not exactly the same. Syntactic details like semi-colons are omitted, and input and output is described in abstract terms.

Complete the program based on the process shown in the Figure 3 flowchart. Note the first line of code declares all 4 variables as type int. Add assignment statements and print statements to compute and print the slices per person and leftover slices. Use System.out.println for output.

1.4.6. Storing User Input in Variables ¶

Variables are a powerful abstraction in programming because the same algorithm can be used with different input values saved in variables.

Figure 4: Program input and output ¶

A Java program can ask the user to type in one or more values. The Java class Scanner is used to read from the keyboard input stream, which is referenced by System.in . Normally the keyboard input is typed into a console window, but since this is running in a browser you will type in a small textbox window displayed below the code. The code below shows an example of prompting the user to enter a name and then printing a greeting. The code String name = scan.nextLine() gets the string value you enter as program input and then stores the value in a variable.

Run the program a few times, typing in a different name. The code works for any name: behold, the power of variables!

Run this program to read in a name from the input stream. You can type a different name in the input window shown below the code.

Try stepping through the code with the CodeLens tool to see how the name variable is assigned to the value read by the scanner. You will have to click “Hide CodeLens” and then “Show in CodeLens” to enter a different name for input.

The Scanner class has several useful methods for reading user input. A token is a sequence of characters separated by white space.

Run this program to read in an integer from the input stream. You can type a different integer value in the input window shown below the code.

A rhomboid (slanted rectangle) is used in a flowchart to depict data flowing into and out of a program. The previous flowchart in Figure 3 used a rhomboid to indicate program output. A rhomboid is also used to denote reading a value from the input stream.

Figure 5: Flow Chart Reading User Input ¶

Figure 5 contains an updated version of the pizza calculator process. The first two steps have been altered to initialize the pizzaSlices and numPeople variables by reading two values from the input stream. In Java this will be done using a Scanner object and reading from System.in.

Complete the program based on the process shown in the Figure 5 flowchart. The program should scan two integer values to initialize pizzaSlices and numPeople. Run the program a few times to experiment with different values for input. What happens if you enter 0 for the number of people? The program will bomb due to division by zero! We will see how to prevent this in a later lesson.

The program below reads two integer values from the input stream and attempts to print the sum. Unfortunately there is a problem with the last line of code that prints the sum.

Run the program and look at the result. When the input is 5 and 7 , the output is Sum is 57 . Both of the + operators in the print statement are performing string concatenation. While the first + operator should perform string concatenation, the second + operator should perform addition. You can force the second + operator to perform addition by putting the arithmetic expression in parentheses ( num1 + num2 ) .

More information on using the Scanner class can be found here https://www.w3schools.com/java/java_user_input.asp

1.4.7. Programming Challenge : Dog Years ¶

In this programming challenge, you will calculate your age, and your pet’s age from your birthdates, and your pet’s age in dog years. In the code below, type in the current year, the year you were born, the year your dog or cat was born (if you don’t have one, make one up!) in the variables below. Then write formulas in assignment statements to calculate how old you are, how old your dog or cat is, and how old they are in dog years which is 7 times a human year. Finally, print it all out.

Calculate your age and your pet’s age from the birthdates, and then your pet’s age in dog years. If you want an extra challenge, try reading the values using a Scanner.

1.4.8. Summary ¶

Arithmetic expressions include expressions of type int and double.

The arithmetic operators consist of +, -, * , /, and % (modulo for the remainder in division).

An arithmetic operation that uses two int values will evaluate to an int value. With integer division, any decimal part in the result will be thrown away, essentially rounding down the answer to a whole number.

An arithmetic operation that uses at least one double value will evaluate to a double value.

Operators can be used to construct compound expressions.

During evaluation, operands are associated with operators according to operator precedence to determine how they are grouped. (*, /, % have precedence over + and -, unless parentheses are used to group those.)

An attempt to divide an integer by zero will result in an ArithmeticException to occur.

The assignment operator (=) allows a program to initialize or change the value stored in a variable. The value of the expression on the right is stored in the variable on the left.

During execution, expressions are evaluated to produce a single value.

The value of an expression has a type based on the evaluation of the expression.

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Java provides many types of operators to perform a variety of calculations and functions, such as logical , arithmetic , relational , and others. With so many operators to choose from, it helps to group them based on the type of functionality they provide. This programming tutorial will focus on Java’s numerous a ssignment operators.

Before we begin, however, you may want to bookmark our other tutorials on Java operators, which include:

• Arithmetic Operators
• Comparison Operators
• Conditional Operators
• Logical Operators
• Bitwise and Shift Operators

Assignment Operators in Java

As the name conveys, assignment operators are used to assign values to a variable using the following syntax:

The left side operand of the assignment operator must be a variable, whereas the right side operand of the assignment operator may be a literal value or another variable. Moreover, the value or variable on the right side must be of the same data type of the operand on the left side. Otherwise, the compiler will raise an error. Assignment operators have a right to left associativity in that the value given on the right-hand side of the operator is assigned to the variable on the left. Therefore, the right-hand side variable must be declared before assignment.

You can learn more about variables in our programming tutorial: Working with Java Variables .

Types of Assignment Operators in Java

Java assignment operators are classified into two types: simple and compound .

The Simple assignment operator is the equals ( = ) sign, which is the most straightforward of the bunch. It simply assigns the value or variable on the right to the variable on the left.

Compound operators are comprised of both an arithmetic, bitwise, or shift operator in addition to the equals ( = ) sign.

Equals Operator (=) Java Example

First, let’s learn to use the one-and-only simple assignment operator – the Equals ( = ) operator – with the help of a Java program. It includes two assignments: a literal value to num1 and the num1 variable to num2 , after which both are printed to the console to show that the values have been assigned to the numbers:

The += Operator Java Example

A compound of the + and = operators, the += adds the current value of the variable on the left to the value on the right before assigning the result to the operand on the left. Here is some sample code to demonstrate how to use the += operator in Java:

The -= Operator Java Example

Made up of the – and = operators, the -= first subtracts the variable’s value on the right from the current value of the variable on the left before assigning the result to the operand on the left. We can see it at work below in the following code example showing how to decrement in Java using the -= operator:

The *= Operator Java Example

This Java operator is comprised of the * and = operators. It operates by multiplying the current value of the variable on the left to the value on the right and then assigning the result to the operand on the left. Here’s a program that shows the *= operator in action:

The /= Operator Java Example

A combination of the / and = operators, the /= Operator divides the current value of the variable on the left by the value on the right and then assigns the quotient to the operand on the left. Here is some example code showing how to use the  /= operator in Java:

%= Operator Java Example

The %= operator includes both the % and = operators. As seen in the program below, it divides the current value of the variable on the left by the value on the right and then assigns the remainder to the operand on the left:

Compound Bitwise and Shift Operators in Java

The Bitwise and Shift Operators that we just recently covered can also be utilized in compound form as seen in the list below:

• &= – Compound bitwise Assignment operator.
• ^= – Compound bitwise ^ assignment operator.
• >>= – Compound right shift assignment operator.
• >>>= – Compound right shift filled 0 assignment operator.
• <<= – Compound left shift assignment operator.

The following program demonstrates the working of all the Compound Bitwise and Shift Operators :

Final Thoughts on Java Assignment Operators

This programming tutorial presented an overview of Java’s simple and compound assignment Operators. An essential building block to any programming language, developers would be unable to store any data in their programs without them. Though not quite as indispensable as the equals operator, compound operators are great time savers, allowing you to perform arithmetic and bitwise operations and assignment in a single line of code.

Read more Java programming tutorials and guides to software development .

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1.7 Java | Assignment Statements & Expressions

An assignment statement designates a value for a variable. An assignment statement can be used as an expression in Java.

After a variable is declared, you can assign a value to it by using an assignment statement . In Java, the equal sign = is used as the assignment operator . The syntax for assignment statements is as follows:

An expression represents a computation involving values, variables, and operators that, when taking them together, evaluates to a value. For example, consider the following code:

You can use a variable in an expression. A variable can also be used on both sides of the =  operator. For example:

In the above assignment statement, the result of x + 1  is assigned to the variable x . Let’s say that x is 1 before the statement is executed, and so becomes 2 after the statement execution.

To assign a value to a variable, you must place the variable name to the left of the assignment operator. Thus the following statement is wrong:

Note that the math equation  x = 2 * x + 1  ≠ the Java expression x = 2 * x + 1

Which is equivalent to:

And this statement

is equivalent to:

Note: The data type of a variable on the left must be compatible with the data type of a value on the right. For example, int x = 1.0 would be illegal, because the data type of x is int (integer) and does not accept the double value 1.0 without Type Casting .

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Java SE > Java SE Specifications > Java Virtual Machine Specification

Chapter 6. The Java Virtual Machine Instruction Set

Table of Contents

A Java Virtual Machine instruction consists of an opcode specifying the operation to be performed, followed by zero or more operands embodying values to be operated upon. This chapter gives details about the format of each Java Virtual Machine instruction and the operation it performs.

6.1. Assumptions: The Meaning of "Must"

The description of each instruction is always given in the context of Java Virtual Machine code that satisfies the static and structural constraints of §4 . In the description of individual Java Virtual Machine instructions, we frequently state that some situation "must" or "must not" be the case: "The value2 must be of type int ." The constraints of §4 guarantee that all such expectations will in fact be met. If some constraint (a "must" or "must not") in an instruction description is not satisfied at run time, the behavior of the Java Virtual Machine is undefined.

The Java Virtual Machine checks that Java Virtual Machine code satisfies the static and structural constraints at link time using a class file verifier ( §4.10 ). Thus, a Java Virtual Machine will only attempt to execute code from valid class files. Performing verification at link time is attractive in that the checks are performed just once, substantially reducing the amount of work that must be done at run time. Other implementation strategies are possible, provided that they comply with The Java Language Specification, Java SE 7 Edition and The Java Virtual Machine Specification, Java SE 7 Edition .

6.2. Reserved Opcodes

In addition to the opcodes of the instructions specified later in this chapter, which are used in class files ( §4 ), three opcodes are reserved for internal use by a Java Virtual Machine implementation. If the instruction set of the Java Virtual Machine is extended in the future, these reserved opcodes are guaranteed not to be used.

Two of the reserved opcodes, numbers 254 (0xfe) and 255 (0xff), have the mnemonics impdep1 and impdep2 , respectively. These instructions are intended to provide "back doors" or traps to implementation-specific functionality implemented in software and hardware, respectively. The third reserved opcode, number 202 (0xca), has the mnemonic breakpoint and is intended to be used by debuggers to implement breakpoints.

Although these opcodes have been reserved, they may be used only inside a Java Virtual Machine implementation. They cannot appear in valid class files. Tools such as debuggers or JIT code generators ( §2.13 ) that might directly interact with Java Virtual Machine code that has been already loaded and executed may encounter these opcodes. Such tools should attempt to behave gracefully if they encounter any of these reserved instructions.

6.3. Virtual Machine Errors

A Java Virtual Machine implementation throws an object that is an instance of a subclass of the class VirtualMethodError when an internal error or resource limitation prevents it from implementing the semantics described in this chapter. This specification cannot predict where internal errors or resource limitations may be encountered and does not mandate precisely when they can be reported. Thus, any of the VirtualMethodError subclasses defined below may be thrown at any time during the operation of the Java Virtual Machine:

InternalError : An internal error has occurred in the Java Virtual Machine implementation because of a fault in the software implementing the virtual machine, a fault in the underlying host system software, or a fault in the hardware. This error is delivered asynchronously ( §2.10 ) when it is detected and may occur at any point in a program.

OutOfMemoryError : The Java Virtual Machine implementation has run out of either virtual or physical memory, and the automatic storage manager was unable to reclaim enough memory to satisfy an object creation request.

StackOverflowError : The Java Virtual Machine implementation has run out of stack space for a thread, typically because the thread is doing an unbounded number of recursive invocations as a result of a fault in the executing program.

UnknownError : An exception or error has occurred, but the Java Virtual Machine implementation is unable to report the actual exception or error.

6.4. Format of Instruction Descriptions

Java Virtual Machine instructions are represented in this chapter by entries of the form shown below, in alphabetical order and each beginning on a new page.

Short description of the instruction

mnemonic operand1 operand2 ...

mnemonic = opcode

Operand Stack

..., value1 , value2 →

..., value3

Description

A longer description detailing constraints on operand stack contents or constant pool entries, the operation performed, the type of the results, etc.

Linking Exceptions

If any linking exceptions may be thrown by the execution of this instruction, they are set off one to a line, in the order in which they must be thrown.

Run-time Exceptions

If any run-time exceptions can be thrown by the execution of an instruction, they are set off one to a line, in the order in which they must be thrown.

Other than the linking and run-time exceptions, if any, listed for an instruction, that instruction must not throw any run-time exceptions except for instances of VirtualMethodError or its subclasses.

Comments not strictly part of the specification of an instruction are set aside as notes at the end of the description.

Each cell in the instruction format diagram represents a single 8-bit byte. The instruction's mnemonic is its name. Its opcode is its numeric representation and is given in both decimal and hexadecimal forms. Only the numeric representation is actually present in the Java Virtual Machine code in a class file.

Keep in mind that there are "operands" generated at compile time and embedded within Java Virtual Machine instructions, as well as "operands" calculated at run time and supplied on the operand stack. Although they are supplied from several different areas, all these operands represent the same thing: values to be operated upon by the Java Virtual Machine instruction being executed. By implicitly taking many of its operands from its operand stack, rather than representing them explicitly in its compiled code as additional operand bytes, register numbers, etc., the Java Virtual Machine's code stays compact.

Some instructions are presented as members of a family of related instructions sharing a single description, format, and operand stack diagram. As such, a family of instructions includes several opcodes and opcode mnemonics; only the family mnemonic appears in the instruction format diagram, and a separate forms line lists all member mnemonics and opcodes. For example, the Forms line for the lconst_<l> family of instructions, giving mnemonic and opcode information for the two instructions in that family ( lconst_0 and lconst_1 ), is

lconst_0 = 9 (0x9)

lconst_1 = 10 (0xa)

In the description of the Java Virtual Machine instructions, the effect of an instruction's execution on the operand stack ( §2.6.2 ) of the current frame ( §2.6 ) is represented textually, with the stack growing from left to right and each value represented separately. Thus,

..., result

shows an operation that begins by having value2 on top of the operand stack with value1 just beneath it. As a result of the execution of the instruction, value1 and value2 are popped from the operand stack and replaced by result value, which has been calculated by the instruction. The remainder of the operand stack, represented by an ellipsis (...), is unaffected by the instruction's execution.

Values of types long and double are represented by a single entry on the operand stack.

In The Java Virtual Machine Specification, First Edition , values on the operand stack of types long and double were each represented in the stack diagram by two entries.

6.5. Instructions

Load reference from array

aaload = 50 (0x32)

..., arrayref , index →

The arrayref must be of type reference and must refer to an array whose components are of type reference . The index must be of type int . Both arrayref and index are popped from the operand stack. The reference value in the component of the array at index is retrieved and pushed onto the operand stack.

If arrayref is null , aaload throws a NullPointerException .

Otherwise, if index is not within the bounds of the array referenced by arrayref , the aaload instruction throws an ArrayIndexOutOfBoundsException .

Store into reference array

aastore = 83 (0x53)

..., arrayref , index , value →

The arrayref must be of type reference and must refer to an array whose components are of type reference . The index must be of type int and value must be of type reference . The arrayref , index , and value are popped from the operand stack. The reference value is stored as the component of the array at index .

At run time, the type of value must be compatible with the type of the components of the array referenced by arrayref . Specifically, assignment of a value of reference type S (source) to an array component of reference type T (target) is allowed only if:

If S is a class type, then:

If T is a class type, then S must be the same class as T , or S must be a subclass of T ;

If T is an interface type, then S must implement interface T .

If S is an interface type, then:

If T is a class type, then T must be Object .

If T is an interface type, then T must be the same interface as S or a superinterface of S .

If S is an array type, namely, the type SC [] , that is, an array of components of type SC , then:

If T is an interface type, then T must be one of the interfaces implemented by arrays (JLS §4.10.3).

If T is an array type TC [] , that is, an array of components of type TC , then one of the following must be true:

TC and SC are the same primitive type.

TC and SC are reference types, and type SC is assignable to TC by these run-time rules.

If arrayref is null , aastore throws a NullPointerException .

Otherwise, if index is not within the bounds of the array referenced by arrayref , the aastore instruction throws an ArrayIndexOutOfBoundsException .

Otherwise, if arrayref is not null and the actual type of value is not assignment compatible (JLS §5.2) with the actual type of the components of the array, aastore throws an ArrayStoreException .

aconst_null

aconst_null = 1 (0x1)

... →

Push the null object reference onto the operand stack.

The Java Virtual Machine does not mandate a concrete value for null .

Load reference from local variable

aload index

aload = 25 (0x19)

..., objectref

The index is an unsigned byte that must be an index into the local variable array of the current frame ( §2.6 ). The local variable at index must contain a reference . The objectref in the local variable at index is pushed onto the operand stack.

The aload instruction cannot be used to load a value of type returnAddress from a local variable onto the operand stack. This asymmetry with the astore instruction ( § astore ) is intentional.

The aload opcode can be used in conjunction with the wide instruction ( § wide ) to access a local variable using a two-byte unsigned index.

aload_<n>

aload_0 = 42 (0x2a)

aload_1 = 43 (0x2b)

aload_2 = 44 (0x2c)

aload_3 = 45 (0x2d)

The < n > must be an index into the local variable array of the current frame ( §2.6 ). The local variable at < n > must contain a reference . The objectref in the local variable at < n > is pushed onto the operand stack.

An aload_<n> instruction cannot be used to load a value of type returnAddress from a local variable onto the operand stack. This asymmetry with the corresponding astore_<n> instruction ( § astore_<n> ) is intentional.

Each of the aload_<n> instructions is the same as aload with an index of < n >, except that the operand < n > is implicit.

Create new array of reference

anewarray indexbyte1 indexbyte2

anewarray = 189 (0xbd)

..., count →

..., arrayref

The count must be of type int . It is popped off the operand stack. The count represents the number of components of the array to be created. The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class ( §2.6 ), where the value of the index is ( indexbyte1 << 8) | indexbyte2 . The run-time constant pool item at that index must be a symbolic reference to a class, array, or interface type. The named class, array, or interface type is resolved ( §5.4.3.1 ). A new array with components of that type, of length count , is allocated from the garbage-collected heap, and a reference arrayref to this new array object is pushed onto the operand stack. All components of the new array are initialized to null , the default value for reference types ( §2.4 ).

During resolution of the symbolic reference to the class, array, or interface type, any of the exceptions documented in §5.4.3.1 can be thrown.

Otherwise, if count is less than zero, the anewarray instruction throws a NegativeArraySizeException .

The anewarray instruction is used to create a single dimension of an array of object references or part of a multidimensional array.

Return reference from method

areturn = 176 (0xb0)

..., objectref →

The objectref must be of type reference and must refer to an object of a type that is assignment compatible (JLS §5.2) with the type represented by the return descriptor ( §4.3.3 ) of the current method. If the current method is a synchronized method, the monitor entered or reentered on invocation of the method is updated and possibly exited as if by execution of a monitorexit instruction ( § monitorexit ) in the current thread. If no exception is thrown, objectref is popped from the operand stack of the current frame ( §2.6 ) and pushed onto the operand stack of the frame of the invoker. Any other values on the operand stack of the current method are discarded.

The interpreter then reinstates the frame of the invoker and returns control to the invoker.

If the Java Virtual Machine implementation does not enforce the rules on structured locking described in §2.11.10 , then if the current method is a synchronized method and the current thread is not the owner of the monitor entered or reentered on invocation of the method, areturn throws an IllegalMonitorStateException . This can happen, for example, if a synchronized method contains a monitorexit instruction, but no monitorenter instruction, on the object on which the method is synchronized.

Otherwise, if the Java Virtual Machine implementation enforces the rules on structured locking described in §2.11.10 and if the first of those rules is violated during invocation of the current method, then areturn throws an IllegalMonitorStateException .

arraylength

Get length of array

arraylength = 190 (0xbe)

..., arrayref →

..., length

The arrayref must be of type reference and must refer to an array. It is popped from the operand stack. The length of the array it references is determined. That length is pushed onto the operand stack as an int .

If the arrayref is null , the arraylength instruction throws a NullPointerException .

Store reference into local variable

astore index

astore = 58 (0x3a)

The index is an unsigned byte that must be an index into the local variable array of the current frame ( §2.6 ). The objectref on the top of the operand stack must be of type returnAddress or of type reference . It is popped from the operand stack, and the value of the local variable at index is set to objectref .

The astore instruction is used with an objectref of type returnAddress when implementing the finally clause of the Java programming language ( §3.13 ).

The aload instruction ( § aload ) cannot be used to load a value of type returnAddress from a local variable onto the operand stack. This asymmetry with the astore instruction is intentional.

The astore opcode can be used in conjunction with the wide instruction ( § wide ) to access a local variable using a two-byte unsigned index.

astore_<n>

astore_0 = 75 (0x4b)

astore_1 = 76 (0x4c)

astore_2 = 77 (0x4d)

astore_3 = 78 (0x4e)

The < n > must be an index into the local variable array of the current frame ( §2.6 ). The objectref on the top of the operand stack must be of type returnAddress or of type reference . It is popped from the operand stack, and the value of the local variable at < n > is set to objectref .

An astore_<n> instruction is used with an objectref of type returnAddress when implementing the finally clauses of the Java programming language ( §3.13 ).

An aload_<n> instruction ( § aload_<n> ) cannot be used to load a value of type returnAddress from a local variable onto the operand stack. This asymmetry with the corresponding astore_<n> instruction is intentional.

Each of the astore_<n> instructions is the same as astore with an index of < n >, except that the operand < n > is implicit.

Throw exception or error

athrow = 191 (0xbf)

The objectref must be of type reference and must refer to an object that is an instance of class Throwable or of a subclass of Throwable . It is popped from the operand stack. The objectref is then thrown by searching the current method ( §2.6 ) for the first exception handler that matches the class of objectref , as given by the algorithm in §2.10 .

If an exception handler that matches objectref is found, it contains the location of the code intended to handle this exception. The pc register is reset to that location, the operand stack of the current frame is cleared, objectref is pushed back onto the operand stack, and execution continues.

If no matching exception handler is found in the current frame, that frame is popped. If the current frame represents an invocation of a synchronized method, the monitor entered or reentered on invocation of the method is exited as if by execution of a monitorexit instruction ( § monitorexit ). Finally, the frame of its invoker is reinstated, if such a frame exists, and the objectref is rethrown. If no such frame exists, the current thread exits.

If objectref is null , athrow throws a NullPointerException instead of objectref .

Otherwise, if the Java Virtual Machine implementation does not enforce the rules on structured locking described in §2.11.10 , then if the method of the current frame is a synchronized method and the current thread is not the owner of the monitor entered or reentered on invocation of the method, athrow throws an IllegalMonitorStateException instead of the object previously being thrown. This can happen, for example, if an abruptly completing synchronized method contains a monitorexit instruction, but no monitorenter instruction, on the object on which the method is synchronized.

Otherwise, if the Java Virtual Machine implementation enforces the rules on structured locking described in §2.11.10 and if the first of those rules is violated during invocation of the current method, then athrow throws an IllegalMonitorStateException instead of the object previously being thrown.

The operand stack diagram for the athrow instruction may be misleading: If a handler for this exception is matched in the current method, the athrow instruction discards all the values on the operand stack, then pushes the thrown object onto the operand stack. However, if no handler is matched in the current method and the exception is thrown farther up the method invocation chain, then the operand stack of the method (if any) that handles the exception is cleared and objectref is pushed onto that empty operand stack. All intervening frames from the method that threw the exception up to, but not including, the method that handles the exception are discarded.

Load byte or boolean from array

baload = 51 (0x33)

The arrayref must be of type reference and must refer to an array whose components are of type byte or of type boolean . The index must be of type int . Both arrayref and index are popped from the operand stack. The byte value in the component of the array at index is retrieved, sign-extended to an int value , and pushed onto the top of the operand stack.

If arrayref is null , baload throws a NullPointerException .

Otherwise, if index is not within the bounds of the array referenced by arrayref , the baload instruction throws an ArrayIndexOutOfBoundsException .

The baload instruction is used to load values from both byte and boolean arrays. In Oracle's Java Virtual Machine implementation, boolean arrays - that is, arrays of type T_BOOLEAN ( §2.2 , § newarray ) - are implemented as arrays of 8-bit values. Other implementations may implement packed boolean arrays; the baload instruction of such implementations must be used to access those arrays.

Store into byte or boolean array

bastore = 84 (0x54)

The arrayref must be of type reference and must refer to an array whose components are of type byte or of type boolean . The index and the value must both be of type int . The arrayref , index , and value are popped from the operand stack. The int value is truncated to a byte and stored as the component of the array indexed by index .

If arrayref is null , bastore throws a NullPointerException .

Otherwise, if index is not within the bounds of the array referenced by arrayref , the bastore instruction throws an ArrayIndexOutOfBoundsException .

The bastore instruction is used to store values into both byte and boolean arrays. In Oracle's Java Virtual Machine implementation, boolean arrays - that is, arrays of type T_BOOLEAN ( §2.2 , § newarray ) - are implemented as arrays of 8-bit values. Other implementations may implement packed boolean arrays; in such implementations the bastore instruction must be able to store boolean values into packed boolean arrays as well as byte values into byte arrays.

bipush byte

bipush = 16 (0x10)

The immediate byte is sign-extended to an int value . That value is pushed onto the operand stack.

Load char from array

caload = 52 (0x34)

The arrayref must be of type reference and must refer to an array whose components are of type char . The index must be of type int . Both arrayref and index are popped from the operand stack. The component of the array at index is retrieved and zero-extended to an int value . That value is pushed onto the operand stack.

If arrayref is null , caload throws a NullPointerException .

Otherwise, if index is not within the bounds of the array referenced by arrayref , the caload instruction throws an ArrayIndexOutOfBoundsException .

Store into char array

castore = 85 (0x55)

The arrayref must be of type reference and must refer to an array whose components are of type char . The index and the value must both be of type int . The arrayref , index , and value are popped from the operand stack. The int value is truncated to a char and stored as the component of the array indexed by index .

If arrayref is null , castore throws a NullPointerException .

Otherwise, if index is not within the bounds of the array referenced by arrayref , the castore instruction throws an ArrayIndexOutOfBoundsException .

Check whether object is of given type

checkcast indexbyte1 indexbyte2

checkcast = 192 (0xc0)

The objectref must be of type reference . The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class ( §2.6 ), where the value of the index is ( indexbyte1 << 8) | indexbyte2 . The run-time constant pool item at the index must be a symbolic reference to a class, array, or interface type.

If objectref is null , then the operand stack is unchanged.

Otherwise, the named class, array, or interface type is resolved ( §5.4.3.1 ). If objectref can be cast to the resolved class, array, or interface type, the operand stack is unchanged; otherwise, the checkcast instruction throws a ClassCastException .

The following rules are used to determine whether an objectref that is not null can be cast to the resolved type: if S is the class of the object referred to by objectref and T is the resolved class, array, or interface type, checkcast determines whether objectref can be cast to type T as follows:

If S is an ordinary (nonarray) class, then:

If S is a class representing the array type SC [] , that is, an array of components of type SC , then:

TC and SC are reference types, and type SC can be cast to TC by recursive application of these rules.

Run-time Exception

Otherwise, if objectref cannot be cast to the resolved class, array, or interface type, the checkcast instruction throws a ClassCastException .

The checkcast instruction is very similar to the instanceof instruction ( § instanceof ). It differs in its treatment of null , its behavior when its test fails ( checkcast throws an exception, instanceof pushes a result code), and its effect on the operand stack.

Convert double to float

d2f = 144 (0x90)

..., value →

The value on the top of the operand stack must be of type double . It is popped from the operand stack and undergoes value set conversion ( §2.8.3 ) resulting in value '. Then value ' is converted to a float result using IEEE 754 round to nearest mode. The result is pushed onto the operand stack.

Where an d2f instruction is FP-strict ( §2.8.2 ), the result of the conversion is always rounded to the nearest representable value in the float value set ( §2.3.2 ).

Where an d2f instruction is not FP-strict, the result of the conversion may be taken from the float-extended-exponent value set ( §2.3.2 ); it is not necessarily rounded to the nearest representable value in the float value set.

A finite value ' too small to be represented as a float is converted to a zero of the same sign; a finite value ' too large to be represented as a float is converted to an infinity of the same sign. A double NaN is converted to a float NaN.

The d2f instruction performs a narrowing primitive conversion (JLS §5.1.3). It may lose information about the overall magnitude of value ' and may also lose precision.

Convert double to int

d2i = 142 (0x8e)

The value on the top of the operand stack must be of type double . It is popped from the operand stack and undergoes value set conversion ( §2.8.3 ) resulting in value '. Then value ' is converted to an int . The result is pushed onto the operand stack:

If the value ' is NaN, the result of the conversion is an int 0.

Otherwise, if the value ' is not an infinity, it is rounded to an integer value V , rounding towards zero using IEEE 754 round towards zero mode. If this integer value V can be represented as an int , then the result is the int value V .

Otherwise, either the value ' must be too small (a negative value of large magnitude or negative infinity), and the result is the smallest representable value of type int , or the value ' must be too large (a positive value of large magnitude or positive infinity), and the result is the largest representable value of type int .

The d2i instruction performs a narrowing primitive conversion (JLS §5.1.3). It may lose information about the overall magnitude of value ' and may also lose precision.

Convert double to long

d2l = 143 (0x8f)

The value on the top of the operand stack must be of type double . It is popped from the operand stack and undergoes value set conversion ( §2.8.3 ) resulting in value '. Then value ' is converted to a long . The result is pushed onto the operand stack:

If the value ' is NaN, the result of the conversion is a long 0.

Otherwise, if the value ' is not an infinity, it is rounded to an integer value V , rounding towards zero using IEEE 754 round towards zero mode. If this integer value V can be represented as a long , then the result is the long value V .

Otherwise, either the value ' must be too small (a negative value of large magnitude or negative infinity), and the result is the smallest representable value of type long , or the value ' must be too large (a positive value of large magnitude or positive infinity), and the result is the largest representable value of type long .

The d2l instruction performs a narrowing primitive conversion (JLS §5.1.3). It may lose information about the overall magnitude of value ' and may also lose precision.

dadd = 99 (0x63)

Both value1 and value2 must be of type double . The values are popped from the operand stack and undergo value set conversion ( §2.8.3 ), resulting in value1 ' and value2 '. The double result is value1 ' + value2 '. The result is pushed onto the operand stack.

The result of a dadd instruction is governed by the rules of IEEE arithmetic:

If either value1 ' or value2 ' is NaN, the result is NaN.

The sum of two infinities of opposite sign is NaN.

The sum of two infinities of the same sign is the infinity of that sign.

The sum of an infinity and any finite value is equal to the infinity.

The sum of two zeroes of opposite sign is positive zero.

The sum of two zeroes of the same sign is the zero of that sign.

The sum of a zero and a nonzero finite value is equal to the nonzero value.

The sum of two nonzero finite values of the same magnitude and opposite sign is positive zero.

In the remaining cases, where neither operand is an infinity, a zero, or NaN and the values have the same sign or have different magnitudes, the sum is computed and rounded to the nearest representable value using IEEE 754 round to nearest mode. If the magnitude is too large to represent as a double , we say the operation overflows; the result is then an infinity of appropriate sign. If the magnitude is too small to represent as a double , we say the operation underflows; the result is then a zero of appropriate sign.

The Java Virtual Machine requires support of gradual underflow as defined by IEEE 754. Despite the fact that overflow, underflow, or loss of precision may occur, execution of a dadd instruction never throws a run-time exception.

Load double from array

daload = 49 (0x31)

The arrayref must be of type reference and must refer to an array whose components are of type double . The index must be of type int . Both arrayref and index are popped from the operand stack. The double value in the component of the array at index is retrieved and pushed onto the operand stack.

If arrayref is null , daload throws a NullPointerException .

Otherwise, if index is not within the bounds of the array referenced by arrayref , the daload instruction throws an ArrayIndexOutOfBoundsException .

Store into double array

dastore = 82 (0x52)

The arrayref must be of type reference and must refer to an array whose components are of type double . The index must be of type int , and value must be of type double . The arrayref , index , and value are popped from the operand stack. The double value undergoes value set conversion ( §2.8.3 ), resulting in value ', which is stored as the component of the array indexed by index .

If arrayref is null , dastore throws a NullPointerException .

Otherwise, if index is not within the bounds of the array referenced by arrayref , the dastore instruction throws an ArrayIndexOutOfBoundsException .

dcmp<op>

Compare double

dcmpg = 152 (0x98)

dcmpl = 151 (0x97)

Both value1 and value2 must be of type double . The values are popped from the operand stack and undergo value set conversion ( §2.8.3 ), resulting in value1 ' and value2 '. A floating-point comparison is performed:

If value1 ' is greater than value2 ', the int value 1 is pushed onto the operand stack.

Otherwise, if value1 ' is equal to value2 ', the int value 0 is pushed onto the operand stack.

Otherwise, if value1 ' is less than value2 ', the int value -1 is pushed onto the operand stack.

Otherwise, at least one of value1 ' or value2 ' is NaN. The dcmpg instruction pushes the int value 1 onto the operand stack and the dcmpl instruction pushes the int value -1 onto the operand stack.

Floating-point comparison is performed in accordance with IEEE 754. All values other than NaN are ordered, with negative infinity less than all finite values and positive infinity greater than all finite values. Positive zero and negative zero are considered equal.

The dcmpg and dcmpl instructions differ only in their treatment of a comparison involving NaN. NaN is unordered, so any double comparison fails if either or both of its operands are NaN. With both dcmpg and dcmpl available, any double comparison may be compiled to push the same result onto the operand stack whether the comparison fails on non-NaN values or fails because it encountered a NaN. For more information, see §3.5 .

dconst_<d>

Push double

dconst_0 = 14 (0xe)

dconst_1 = 15 (0xf)

..., < d >

Push the double constant < d > (0.0 or 1.0) onto the operand stack.

Divide double

ddiv = 111 (0x6f)

Both value1 and value2 must be of type double . The values are popped from the operand stack and undergo value set conversion ( §2.8.3 ), resulting in value1 ' and value2 '. The double result is value1 ' / value2 '. The result is pushed onto the operand stack.

The result of a ddiv instruction is governed by the rules of IEEE arithmetic:

If neither value1 ' nor value2 ' is NaN, the sign of the result is positive if both values have the same sign, negative if the values have different signs.

Division of an infinity by an infinity results in NaN.

Division of an infinity by a finite value results in a signed infinity, with the sign-producing rule just given.

Division of a finite value by an infinity results in a signed zero, with the sign-producing rule just given.

Division of a zero by a zero results in NaN; division of zero by any other finite value results in a signed zero, with the sign-producing rule just given.

Division of a nonzero finite value by a zero results in a signed infinity, with the sign-producing rule just given.

In the remaining cases, where neither operand is an infinity, a zero, or NaN, the quotient is computed and rounded to the nearest double using IEEE 754 round to nearest mode. If the magnitude is too large to represent as a double , we say the operation overflows; the result is then an infinity of appropriate sign. If the magnitude is too small to represent as a double , we say the operation underflows; the result is then a zero of appropriate sign.

The Java Virtual Machine requires support of gradual underflow as defined by IEEE 754. Despite the fact that overflow, underflow, division by zero, or loss of precision may occur, execution of a ddiv instruction never throws a run-time exception.

Load double from local variable

dload index

dload = 24 (0x18)

The index is an unsigned byte. Both index and index +1 must be indices into the local variable array of the current frame ( §2.6 ). The local variable at index must contain a double . The value of the local variable at index is pushed onto the operand stack.

The dload opcode can be used in conjunction with the wide instruction ( § wide ) to access a local variable using a two-byte unsigned index.

dload_<n>

dload_0 = 38 (0x26)

dload_1 = 39 (0x27)

dload_2 = 40 (0x28)

dload_3 = 41 (0x29)

Both < n > and < n >+1 must be indices into the local variable array of the current frame ( §2.6 ). The local variable at < n > must contain a double . The value of the local variable at < n > is pushed onto the operand stack.

Each of the dload_<n> instructions is the same as dload with an index of < n >, except that the operand < n > is implicit.

Multiply double

dmul = 107 (0x6b)

Both value1 and value2 must be of type double . The values are popped from the operand stack and undergo value set conversion ( §2.8.3 ), resulting in value1 ' and value2 '. The double result is value1 ' * value2 '. The result is pushed onto the operand stack.

The result of a dmul instruction is governed by the rules of IEEE arithmetic:

If neither value1 ' nor value2 ' is NaN, the sign of the result is positive if both values have the same sign and negative if the values have different signs.

Multiplication of an infinity by a zero results in NaN.

Multiplication of an infinity by a finite value results in a signed infinity, with the sign-producing rule just given.

In the remaining cases, where neither an infinity nor NaN is involved, the product is computed and rounded to the nearest representable value using IEEE 754 round to nearest mode. If the magnitude is too large to represent as a double , we say the operation overflows; the result is then an infinity of appropriate sign. If the magnitude is too small to represent as a double , we say the operation underflows; the result is then a zero of appropriate sign.

The Java Virtual Machine requires support of gradual underflow as defined by IEEE 754. Despite the fact that overflow, underflow, or loss of precision may occur, execution of a dmul instruction never throws a run-time exception.

Negate double

dneg = 119 (0x77)

The value must be of type double . It is popped from the operand stack and undergoes value set conversion ( §2.8.3 ), resulting in value '. The double result is the arithmetic negation of value '. The result is pushed onto the operand stack.

For double values, negation is not the same as subtraction from zero. If x is +0.0 , then 0.0-x equals +0.0 , but -x equals -0.0 . Unary minus merely inverts the sign of a double .

Special cases of interest:

If the operand is NaN, the result is NaN (recall that NaN has no sign).

If the operand is an infinity, the result is the infinity of opposite sign.

If the operand is a zero, the result is the zero of opposite sign.

Remainder double

drem = 115 (0x73)

Both value1 and value2 must be of type double . The values are popped from the operand stack and undergo value set conversion ( §2.8.3 ), resulting in value1 ' and value2 '. The result is calculated and pushed onto the operand stack as a double .

The result of a drem instruction is not the same as that of the so-called remainder operation defined by IEEE 754. The IEEE 754 "remainder" operation computes the remainder from a rounding division, not a truncating division, and so its behavior is not analogous to that of the usual integer remainder operator. Instead, the Java Virtual Machine defines drem to behave in a manner analogous to that of the Java Virtual Machine integer remainder instructions ( irem and lrem ); this may be compared with the C library function fmod .

The result of a drem instruction is governed by these rules:

If neither value1 ' nor value2 ' is NaN, the sign of the result equals the sign of the dividend.

If the dividend is an infinity or the divisor is a zero or both, the result is NaN.

If the dividend is finite and the divisor is an infinity, the result equals the dividend.

If the dividend is a zero and the divisor is finite, the result equals the dividend.

In the remaining cases, where neither operand is an infinity, a zero, or NaN, the floating-point remainder result from a dividend value1 ' and a divisor value2 ' is defined by the mathematical relation result = value1 ' - ( value2 ' * q ), where q is an integer that is negative only if value1 ' / value2 ' is negative, and positive only if value1 ' / value2 ' is positive, and whose magnitude is as large as possible without exceeding the magnitude of the true mathematical quotient of value1 ' and value2 '.

Despite the fact that division by zero may occur, evaluation of a drem instruction never throws a run-time exception. Overflow, underflow, or loss of precision cannot occur.

The IEEE 754 remainder operation may be computed by the library routine Math.IEEEremainder .

Return double from method

dreturn = 175 (0xaf)

The current method must have return type double . The value must be of type double . If the current method is a synchronized method, the monitor entered or reentered on invocation of the method is updated and possibly exited as if by execution of a monitorexit instruction ( § monitorexit ) in the current thread. If no exception is thrown, value is popped from the operand stack of the current frame ( §2.6 ) and undergoes value set conversion ( §2.8.3 ), resulting in value '. The value ' is pushed onto the operand stack of the frame of the invoker. Any other values on the operand stack of the current method are discarded.

The interpreter then returns control to the invoker of the method, reinstating the frame of the invoker.

If the Java Virtual Machine implementation does not enforce the rules on structured locking described in §2.11.10 , then if the current method is a synchronized method and the current thread is not the owner of the monitor entered or reentered on invocation of the method, dreturn throws an IllegalMonitorStateException . This can happen, for example, if a synchronized method contains a monitorexit instruction, but no monitorenter instruction, on the object on which the method is synchronized.

Otherwise, if the Java Virtual Machine implementation enforces the rules on structured locking described in §2.11.10 and if the first of those rules is violated during invocation of the current method, then dreturn throws an IllegalMonitorStateException .

Store double into local variable

dstore index

dstore = 57 (0x39)

The index is an unsigned byte. Both index and index +1 must be indices into the local variable array of the current frame ( §2.6 ). The value on the top of the operand stack must be of type double . It is popped from the operand stack and undergoes value set conversion ( §2.8.3 ), resulting in value '. The local variables at index and index +1 are set to value '.

The dstore opcode can be used in conjunction with the wide instruction ( § wide ) to access a local variable using a two-byte unsigned index.

dstore_<n>

dstore_0 = 71 (0x47)

dstore_1 = 72 (0x48)

dstore_2 = 73 (0x49)

dstore_3 = 74 (0x4a)

Both < n > and < n >+1 must be indices into the local variable array of the current frame ( §2.6 ). The value on the top of the operand stack must be of type double . It is popped from the operand stack and undergoes value set conversion ( §2.8.3 ), resulting in value '. The local variables at < n > and < n >+1 are set to value '.

Each of the dstore_<n> instructions is the same as dstore with an index of < n >, except that the operand < n > is implicit.

Subtract double

dsub = 103 (0x67)

Both value1 and value2 must be of type double . The values are popped from the operand stack and undergo value set conversion ( §2.8.3 ), resulting in value1 ' and value2 '. The double result is value1 ' - value2 '. The result is pushed onto the operand stack.

For double subtraction, it is always the case that a-b produces the same result as a+(-b) . However, for the dsub instruction, subtraction from zero is not the same as negation, because if x is +0.0 , then 0.0-x equals +0.0 , but -x equals -0.0 .

The Java Virtual Machine requires support of gradual underflow as defined by IEEE 754. Despite the fact that overflow, underflow, or loss of precision may occur, execution of a dsub instruction never throws a run-time exception.

Duplicate the top operand stack value

dup = 89 (0x59)

..., value , value

Duplicate the top value on the operand stack and push the duplicated value onto the operand stack.

The dup instruction must not be used unless value is a value of a category 1 computational type ( §2.11.1 ).

Duplicate the top operand stack value and insert two values down

dup_x1 = 90 (0x5a)

..., value2 , value1 →

..., value1 , value2 , value1

Duplicate the top value on the operand stack and insert the duplicated value two values down in the operand stack.

The dup_x1 instruction must not be used unless both value1 and value2 are values of a category 1 computational type ( §2.11.1 ).

Duplicate the top operand stack value and insert two or three values down

dup_x2 = 91 (0x5b)

..., value3 , value2 , value1 →

..., value1 , value3 , value2 , value1

where value1 , value2 , and value3 are all values of a category 1 computational type ( §2.11.1 ).

where value1 is a value of a category 1 computational type and value2 is a value of a category 2 computational type ( §2.11.1 ).

Duplicate the top value on the operand stack and insert the duplicated value two or three values down in the operand stack.

Duplicate the top one or two operand stack values

dup2 = 92 (0x5c)

..., value2 , value1 , value2 , value1

where both value1 and value2 are values of a category 1 computational type ( §2.11.1 ).

where value is a value of a category 2 computational type ( §2.11.1 ).

Duplicate the top one or two values on the operand stack and push the duplicated value or values back onto the operand stack in the original order.

Duplicate the top one or two operand stack values and insert two or three values down

dup2_x1 = 93 (0x5d)

..., value2 , value1 , value3 , value2 , value1

where value1 is a value of a category 2 computational type and value2 is a value of a category 1 computational type ( §2.11.1 ).

Duplicate the top one or two values on the operand stack and insert the duplicated values, in the original order, one value beneath the original value or values in the operand stack.

Duplicate the top one or two operand stack values and insert two, three, or four values down

dup2_x2 = 94 (0x5e)

..., value4 , value3 , value2 , value1 →

..., value2 , value1 , value4 , value3 , value2 , value1

where value1 , value2 , value3 , and value4 are all values of a category 1 computational type ( §2.11.1 ).

where value1 is a value of a category 2 computational type and value2 and value3 are both values of a category 1 computational type ( §2.11.1 ).

where value1 and value2 are both values of a category 1 computational type and value3 is a value of a category 2 computational type ( §2.11.1 ).

where value1 and value2 are both values of a category 2 computational type ( §2.11.1 ).

Duplicate the top one or two values on the operand stack and insert the duplicated values, in the original order, into the operand stack.

Convert float to double

f2d = 141 (0x8d)

The value on the top of the operand stack must be of type float . It is popped from the operand stack and undergoes value set conversion ( §2.8.3 ), resulting in value '. Then value ' is converted to a double result . This result is pushed onto the operand stack.

Where an f2d instruction is FP-strict ( §2.8.2 ) it performs a widening primitive conversion (JLS §5.1.2). Because all values of the float value set ( §2.3.2 ) are exactly representable by values of the double value set ( §2.3.2 ), such a conversion is exact.

Where an f2d instruction is not FP-strict, the result of the conversion may be taken from the double-extended-exponent value set; it is not necessarily rounded to the nearest representable value in the double value set. However, if the operand value is taken from the float-extended-exponent value set and the target result is constrained to the double value set, rounding of value may be required.

Convert float to int

f2i = 139 (0x8b)

The value on the top of the operand stack must be of type float . It is popped from the operand stack and undergoes value set conversion ( §2.8.3 ), resulting in value '. Then value ' is converted to an int result . This result is pushed onto the operand stack:

The f2i instruction performs a narrowing primitive conversion (JLS §5.1.3). It may lose information about the overall magnitude of value ' and may also lose precision.

Convert float to long

f2l = 140 (0x8c)

The value on the top of the operand stack must be of type float . It is popped from the operand stack and undergoes value set conversion ( §2.8.3 ), resulting in value '. Then value ' is converted to a long result . This result is pushed onto the operand stack:

The f2l instruction performs a narrowing primitive conversion (JLS §5.1.3). It may lose information about the overall magnitude of value ' and may also lose precision.

fadd = 98 (0x62)

Both value1 and value2 must be of type float . The values are popped from the operand stack and undergo value set conversion ( §2.8.3 ), resulting in value1 ' and value2 '. The float result is value1 ' + value2 '. The result is pushed onto the operand stack.

The result of an fadd instruction is governed by the rules of IEEE arithmetic:

In the remaining cases, where neither operand is an infinity, a zero, or NaN and the values have the same sign or have different magnitudes, the sum is computed and rounded to the nearest representable value using IEEE 754 round to nearest mode. If the magnitude is too large to represent as a float , we say the operation overflows; the result is then an infinity of appropriate sign. If the magnitude is too small to represent as a float , we say the operation underflows; the result is then a zero of appropriate sign.

The Java Virtual Machine requires support of gradual underflow as defined by IEEE 754. Despite the fact that overflow, underflow, or loss of precision may occur, execution of an fadd instruction never throws a run-time exception.

Load float from array

faload = 48 (0x30)

The arrayref must be of type reference and must refer to an array whose components are of type float . The index must be of type int . Both arrayref and index are popped from the operand stack. The float value in the component of the array at index is retrieved and pushed onto the operand stack.

If arrayref is null , faload throws a NullPointerException .

Otherwise, if index is not within the bounds of the array referenced by arrayref , the faload instruction throws an ArrayIndexOutOfBoundsException .

Store into float array

fastore = 81 (0x51)

The arrayref must be of type reference and must refer to an array whose components are of type float . The index must be of type int , and the value must be of type float . The arrayref , index , and value are popped from the operand stack. The float value undergoes value set conversion ( §2.8.3 ), resulting in value ', and value ' is stored as the component of the array indexed by index .

If arrayref is null , fastore throws a NullPointerException .

Otherwise, if index is not within the bounds of the array referenced by arrayref , the fastore instruction throws an ArrayIndexOutOfBoundsException .

fcmp<op>

Compare float

fcmpg = 150 (0x96)

fcmpl = 149 (0x95)

Both value1 and value2 must be of type float . The values are popped from the operand stack and undergo value set conversion ( §2.8.3 ), resulting in value1 ' and value2 '. A floating-point comparison is performed:

Otherwise, at least one of value1 ' or value2 ' is NaN. The fcmpg instruction pushes the int value 1 onto the operand stack and the fcmpl instruction pushes the int value -1 onto the operand stack.

The fcmpg and fcmpl instructions differ only in their treatment of a comparison involving NaN. NaN is unordered, so any float comparison fails if either or both of its operands are NaN. With both fcmpg and fcmpl available, any float comparison may be compiled to push the same result onto the operand stack whether the comparison fails on non-NaN values or fails because it encountered a NaN. For more information, see §3.5 .

fconst_<f>

fconst_0 = 11 (0xb)

fconst_1 = 12 (0xc)

fconst_2 = 13 (0xd)

..., < f >

Push the float constant < f > (0.0, 1.0, or 2.0) onto the operand stack.

Divide float

fdiv = 110 (0x6e)

Both value1 and value2 must be of type float . The values are popped from the operand stack and undergo value set conversion ( §2.8.3 ), resulting in value1 ' and value2 '. The float result is value1 ' / value2 '. The result is pushed onto the operand stack.

The result of an fdiv instruction is governed by the rules of IEEE arithmetic:

In the remaining cases, where neither operand is an infinity, a zero, or NaN, the quotient is computed and rounded to the nearest float using IEEE 754 round to nearest mode. If the magnitude is too large to represent as a float , we say the operation overflows; the result is then an infinity of appropriate sign. If the magnitude is too small to represent as a float , we say the operation underflows; the result is then a zero of appropriate sign.

The Java Virtual Machine requires support of gradual underflow as defined by IEEE 754. Despite the fact that overflow, underflow, division by zero, or loss of precision may occur, execution of an fdiv instruction never throws a run-time exception.

Load float from local variable

fload index

fload = 23 (0x17)

The index is an unsigned byte that must be an index into the local variable array of the current frame ( §2.6 ). The local variable at index must contain a float . The value of the local variable at index is pushed onto the operand stack.

The fload opcode can be used in conjunction with the wide instruction ( § wide ) to access a local variable using a two-byte unsigned index.

fload_<n>

fload_0 = 34 (0x22)

fload_1 = 35 (0x23)

fload_2 = 36 (0x24)

fload_3 = 37 (0x25)

The < n > must be an index into the local variable array of the current frame ( §2.6 ). The local variable at < n > must contain a float . The value of the local variable at < n > is pushed onto the operand stack.

Each of the fload_<n> instructions is the same as fload with an index of < n >, except that the operand < n > is implicit.

Multiply float

fmul = 106 (0x6a)

Both value1 and value2 must be of type float . The values are popped from the operand stack and undergo value set conversion ( §2.8.3 ), resulting in value1 ' and value2 '. The float result is value1 ' * value2 '. The result is pushed onto the operand stack.

The result of an fmul instruction is governed by the rules of IEEE arithmetic:

If neither value1 ' nor value2 ' is NaN, the sign of the result is positive if both values have the same sign, and negative if the values have different signs.

In the remaining cases, where neither an infinity nor NaN is involved, the product is computed and rounded to the nearest representable value using IEEE 754 round to nearest mode. If the magnitude is too large to represent as a float , we say the operation overflows; the result is then an infinity of appropriate sign. If the magnitude is too small to represent as a float , we say the operation underflows; the result is then a zero of appropriate sign.

The Java Virtual Machine requires support of gradual underflow as defined by IEEE 754. Despite the fact that overflow, underflow, or loss of precision may occur, execution of an fmul instruction never throws a run-time exception.

Negate float

fneg = 118 (0x76)

The value must be of type float . It is popped from the operand stack and undergoes value set conversion ( §2.8.3 ), resulting in value '. The float result is the arithmetic negation of value '. This result is pushed onto the operand stack.

For float values, negation is not the same as subtraction from zero. If x is +0.0 , then 0.0-x equals +0.0 , but -x equals -0.0 . Unary minus merely inverts the sign of a float .

Remainder float

frem = 114 (0x72)

Both value1 and value2 must be of type float . The values are popped from the operand stack and undergo value set conversion ( §2.8.3 ), resulting in value1 ' and value2 '. The result is calculated and pushed onto the operand stack as a float .

The result of an frem instruction is not the same as that of the so-called remainder operation defined by IEEE 754. The IEEE 754 "remainder" operation computes the remainder from a rounding division, not a truncating division, and so its behavior is not analogous to that of the usual integer remainder operator. Instead, the Java Virtual Machine defines frem to behave in a manner analogous to that of the Java Virtual Machine integer remainder instructions ( irem and lrem ); this may be compared with the C library function fmod .

The result of an frem instruction is governed by these rules:

In the remaining cases, where neither operand is an infinity, a zero, or NaN, the floating-point remainder result from a dividend value1 ' and a divisor value2 ' is defined by the mathematical relation result = value1 ' - ( value2 ' * q ), where q is an integer that is negative only if value1 ' / value2 ' is negative and positive only if value1 ' / value2 ' is positive, and whose magnitude is as large as possible without exceeding the magnitude of the true mathematical quotient of value1 ' and value2 '.

Despite the fact that division by zero may occur, evaluation of an frem instruction never throws a run-time exception. Overflow, underflow, or loss of precision cannot occur.

Return float from method

freturn = 174 (0xae)

The current method must have return type float . The value must be of type float . If the current method is a synchronized method, the monitor entered or reentered on invocation of the method is updated and possibly exited as if by execution of a monitorexit instruction ( § monitorexit ) in the current thread. If no exception is thrown, value is popped from the operand stack of the current frame ( §2.6 ) and undergoes value set conversion ( §2.8.3 ), resulting in value '. The value ' is pushed onto the operand stack of the frame of the invoker. Any other values on the operand stack of the current method are discarded.

If the Java Virtual Machine implementation does not enforce the rules on structured locking described in §2.11.10 , then if the current method is a synchronized method and the current thread is not the owner of the monitor entered or reentered on invocation of the method, freturn throws an IllegalMonitorStateException . This can happen, for example, if a synchronized method contains a monitorexit instruction, but no monitorenter instruction, on the object on which the method is synchronized.

Otherwise, if the Java Virtual Machine implementation enforces the rules on structured locking described in §2.11.10 and if the first of those rules is violated during invocation of the current method, then freturn throws an IllegalMonitorStateException .

Store float into local variable

fstore index

fstore = 56 (0x38)

The index is an unsigned byte that must be an index into the local variable array of the current frame ( §2.6 ). The value on the top of the operand stack must be of type float . It is popped from the operand stack and undergoes value set conversion ( §2.8.3 ), resulting in value '. The value of the local variable at index is set to value '.

The fstore opcode can be used in conjunction with the wide instruction ( § wide ) to access a local variable using a two-byte unsigned index.

fstore_<n>

fstore_0 = 67 (0x43)

fstore_1 = 68 (0x44)

fstore_2 = 69 (0x45)

fstore_3 = 70 (0x46)

The < n > must be an index into the local variable array of the current frame ( §2.6 ). The value on the top of the operand stack must be of type float . It is popped from the operand stack and undergoes value set conversion ( §2.8.3 ), resulting in value '. The value of the local variable at < n > is set to value '.

Each of the fstore_<n> instructions is the same as fstore with an index of < n >, except that the operand < n > is implicit.

Subtract float

fsub = 102 (0x66)

Both value1 and value2 must be of type float . The values are popped from the operand stack and undergo value set conversion ( §2.8.3 ), resulting in value1 ' and value2 '. The float result is value1 ' - value2 '. The result is pushed onto the operand stack.

For float subtraction, it is always the case that a-b produces the same result as a+(-b) . However, for the fsub instruction, subtraction from zero is not the same as negation, because if x is +0.0 , then 0.0-x equals +0.0 , but -x equals -0.0 .

The Java Virtual Machine requires support of gradual underflow as defined by IEEE 754. Despite the fact that overflow, underflow, or loss of precision may occur, execution of an fsub instruction never throws a run-time exception.

Fetch field from object

getfield indexbyte1 indexbyte2

getfield = 180 (0xb4)

The objectref , which must be of type reference , is popped from the operand stack. The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class ( §2.6 ), where the value of the index is ( indexbyte1 << 8) | indexbyte2 . The run-time constant pool item at that index must be a symbolic reference to a field ( §5.1 ), which gives the name and descriptor of the field as well as a symbolic reference to the class in which the field is to be found. The referenced field is resolved ( §5.4.3.2 ). The value of the referenced field in objectref is fetched and pushed onto the operand stack.

The type of objectref must not be an array type. If the field is protected ( §4.6 ), and it is a member of a superclass of the current class, and the field is not declared in the same run-time package ( §5.3 ) as the current class, then the class of objectref must be either the current class or a subclass of the current class.

During resolution of the symbolic reference to the field, any of the errors pertaining to field resolution ( §5.4.3.2 ) can be thrown.

Otherwise, if the resolved field is a static field, getfield throws an IncompatibleClassChangeError .

Otherwise, if objectref is null , the getfield instruction throws a NullPointerException .

The getfield instruction cannot be used to access the length field of an array. The arraylength instruction ( § arraylength ) is used instead.

Get static field from class

getstatic indexbyte1 indexbyte2

getstatic = 178 (0xb2)

..., →

The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class ( §2.6 ), where the value of the index is ( indexbyte1 << 8) | indexbyte2 . The run-time constant pool item at that index must be a symbolic reference to a field ( §5.1 ), which gives the name and descriptor of the field as well as a symbolic reference to the class or interface in which the field is to be found. The referenced field is resolved ( §5.4.3.2 ).

On successful resolution of the field, the class or interface that declared the resolved field is initialized ( §5.5 ) if that class or interface has not already been initialized.

The value of the class or interface field is fetched and pushed onto the operand stack.

During resolution of the symbolic reference to the class or interface field, any of the exceptions pertaining to field resolution ( §5.4.3.2 ) can be thrown.

Otherwise, if the resolved field is not a static (class) field or an interface field, getstatic throws an IncompatibleClassChangeError .

Otherwise, if execution of this getstatic instruction causes initialization of the referenced class or interface, getstatic may throw an Error as detailed in §5.5 .

Branch always

goto branchbyte1 branchbyte2

goto = 167 (0xa7)

The unsigned bytes branchbyte1 and branchbyte2 are used to construct a signed 16-bit branchoffset , where branchoffset is ( branchbyte1 << 8) | branchbyte2 . Execution proceeds at that offset from the address of the opcode of this goto instruction. The target address must be that of an opcode of an instruction within the method that contains this goto instruction.

Branch always (wide index)

goto_w branchbyte1 branchbyte2 branchbyte3 branchbyte4

goto_w = 200 (0xc8)

The unsigned bytes branchbyte1 , branchbyte2 , branchbyte3 , and branchbyte4 are used to construct a signed 32-bit branchoffset , where branchoffset is ( branchbyte1 << 24) | ( branchbyte2 << 16) | ( branchbyte3 << 8) | branchbyte4 . Execution proceeds at that offset from the address of the opcode of this goto_w instruction. The target address must be that of an opcode of an instruction within the method that contains this goto_w instruction.

Although the goto_w instruction takes a 4-byte branch offset, other factors limit the size of a method to 65535 bytes ( §4.11 ). This limit may be raised in a future release of the Java Virtual Machine.

Convert int to byte

i2b = 145 (0x91)

The value on the top of the operand stack must be of type int . It is popped from the operand stack, truncated to a byte , then sign-extended to an int result . That result is pushed onto the operand stack.

The i2b instruction performs a narrowing primitive conversion (JLS §5.1.3). It may lose information about the overall magnitude of value . The result may also not have the same sign as value .

Convert int to char

i2c = 146 (0x92)

The value on the top of the operand stack must be of type int . It is popped from the operand stack, truncated to char , then zero-extended to an int result . That result is pushed onto the operand stack.

The i2c instruction performs a narrowing primitive conversion (JLS §5.1.3). It may lose information about the overall magnitude of value . The result (which is always positive) may also not have the same sign as value .

Convert int to double

i2d = 135 (0x87)

The value on the top of the operand stack must be of type int . It is popped from the operand stack and converted to a double result . The result is pushed onto the operand stack.

The i2d instruction performs a widening primitive conversion (JLS §5.1.2). Because all values of type int are exactly representable by type double , the conversion is exact.

Convert int to float

i2f = 134 (0x86)

The value on the top of the operand stack must be of type int . It is popped from the operand stack and converted to the float result using IEEE 754 round to nearest mode. The result is pushed onto the operand stack.

The i2f instruction performs a widening primitive conversion (JLS §5.1.2), but may result in a loss of precision because values of type float have only 24 significand bits.

Convert int to long

i2l = 133 (0x85)

The value on the top of the operand stack must be of type int . It is popped from the operand stack and sign-extended to a long result . That result is pushed onto the operand stack.

The i2l instruction performs a widening primitive conversion (JLS §5.1.2). Because all values of type int are exactly representable by type long , the conversion is exact.

Convert int to short

i2s = 147 (0x93)

The value on the top of the operand stack must be of type int . It is popped from the operand stack, truncated to a short , then sign-extended to an int result . That result is pushed onto the operand stack.

The i2s instruction performs a narrowing primitive conversion (JLS §5.1.3). It may lose information about the overall magnitude of value . The result may also not have the same sign as value .

iadd = 96 (0x60)

Both value1 and value2 must be of type int . The values are popped from the operand stack. The int result is value1 + value2 . The result is pushed onto the operand stack.

The result is the 32 low-order bits of the true mathematical result in a sufficiently wide two's-complement format, represented as a value of type int . If overflow occurs, then the sign of the result may not be the same as the sign of the mathematical sum of the two values.

Despite the fact that overflow may occur, execution of an iadd instruction never throws a run-time exception.

Load int from array

iaload = 46 (0x2e)

The arrayref must be of type reference and must refer to an array whose components are of type int . The index must be of type int . Both arrayref and index are popped from the operand stack. The int value in the component of the array at index is retrieved and pushed onto the operand stack.

If arrayref is null , iaload throws a NullPointerException .

Otherwise, if index is not within the bounds of the array referenced by arrayref , the iaload instruction throws an ArrayIndexOutOfBoundsException .

Boolean AND int

iand = 126 (0x7e)

Both value1 and value2 must be of type int . They are popped from the operand stack. An int result is calculated by taking the bitwise AND (conjunction) of value1 and value2 . The result is pushed onto the operand stack.

Store into int array

iastore = 79 (0x4f)

The arrayref must be of type reference and must refer to an array whose components are of type int . Both index and value must be of type int . The arrayref , index , and value are popped from the operand stack. The int value is stored as the component of the array indexed by index .

If arrayref is null , iastore throws a NullPointerException .

Otherwise, if index is not within the bounds of the array referenced by arrayref , the iastore instruction throws an ArrayIndexOutOfBoundsException .

iconst_<i>

Push int constant

iconst_m1 = 2 (0x2)

iconst_0 = 3 (0x3)

iconst_1 = 4 (0x4)

iconst_2 = 5 (0x5)

iconst_3 = 6 (0x6)

iconst_4 = 7 (0x7)

iconst_5 = 8 (0x8)

..., < i >

Push the int constant < i > (-1, 0, 1, 2, 3, 4 or 5) onto the operand stack.

Each of this family of instructions is equivalent to bipush < i > for the respective value of < i >, except that the operand < i > is implicit.

idiv = 108 (0x6c)

Both value1 and value2 must be of type int . The values are popped from the operand stack. The int result is the value of the Java programming language expression value1 / value2 . The result is pushed onto the operand stack.

An int division rounds towards 0; that is, the quotient produced for int values in n / d is an int value q whose magnitude is as large as possible while satisfying | d · q | ≤ | n |. Moreover, q is positive when | n | ≥ | d | and n and d have the same sign, but q is negative when | n | ≥ | d | and n and d have opposite signs.

There is one special case that does not satisfy this rule: if the dividend is the negative integer of largest possible magnitude for the int type, and the divisor is -1, then overflow occurs, and the result is equal to the dividend. Despite the overflow, no exception is thrown in this case.

If the value of the divisor in an int division is 0, idiv throws an ArithmeticException .

if_acmp<cond>

Branch if reference comparison succeeds

if_acmp<cond> branchbyte1 branchbyte2

if_acmpeq = 165 (0xa5)

if_acmpne = 166 (0xa6)

Both value1 and value2 must be of type reference . They are both popped from the operand stack and compared. The results of the comparison are as follows:

if_acmpeq succeeds if and only if value1 = value2

if_acmpne succeeds if and only if value1 ≠ value2

If the comparison succeeds, the unsigned branchbyte1 and branchbyte2 are used to construct a signed 16-bit offset, where the offset is calculated to be ( branchbyte1 << 8) | branchbyte2 . Execution then proceeds at that offset from the address of the opcode of this if_acmp<cond> instruction. The target address must be that of an opcode of an instruction within the method that contains this if_acmp<cond> instruction.

Otherwise, if the comparison fails, execution proceeds at the address of the instruction following this if_acmp<cond> instruction.

if_icmp<cond>

Branch if int comparison succeeds

if_icmp<cond> branchbyte1 branchbyte2

if_icmpeq = 159 (0x9f)

if_icmpne = 160 (0xa0)

if_icmplt = 161 (0xa1)

if_icmpge = 162 (0xa2)

if_icmpgt = 163 (0xa3)

if_icmple = 164 (0xa4)

Both value1 and value2 must be of type int . They are both popped from the operand stack and compared. All comparisons are signed. The results of the comparison are as follows:

if_icmpeq succeeds if and only if value1 = value2

if_icmpne succeeds if and only if value1 ≠ value2

if_icmplt succeeds if and only if value1 < value2

if_icmple succeeds if and only if value1 ≤ value2

if_icmpgt succeeds if and only if value1 > value2

if_icmpge succeeds if and only if value1 ≥ value2

If the comparison succeeds, the unsigned branchbyte1 and branchbyte2 are used to construct a signed 16-bit offset, where the offset is calculated to be ( branchbyte1 << 8) | branchbyte2 . Execution then proceeds at that offset from the address of the opcode of this if_icmp<cond> instruction. The target address must be that of an opcode of an instruction within the method that contains this if_icmp<cond> instruction.

Otherwise, execution proceeds at the address of the instruction following this if_icmp<cond> instruction.

if<cond>

Branch if int comparison with zero succeeds

if<cond> branchbyte1 branchbyte2

ifeq = 153 (0x99)

ifne = 154 (0x9a)

iflt = 155 (0x9b)

ifge = 156 (0x9c)

ifgt = 157 (0x9d)

ifle = 158 (0x9e)

The value must be of type int . It is popped from the operand stack and compared against zero. All comparisons are signed. The results of the comparisons are as follows:

ifeq succeeds if and only if value = 0

ifne succeeds if and only if value ≠ 0

iflt succeeds if and only if value < 0

ifle succeeds if and only if value ≤ 0

ifgt succeeds if and only if value > 0

ifge succeeds if and only if value ≥ 0

If the comparison succeeds, the unsigned branchbyte1 and branchbyte2 are used to construct a signed 16-bit offset, where the offset is calculated to be ( branchbyte1 << 8) | branchbyte2 . Execution then proceeds at that offset from the address of the opcode of this if<cond> instruction. The target address must be that of an opcode of an instruction within the method that contains this if<cond> instruction.

Otherwise, execution proceeds at the address of the instruction following this if<cond> instruction.

Branch if reference not null

ifnonnull branchbyte1 branchbyte2

ifnonnull = 199 (0xc7)

The value must be of type reference . It is popped from the operand stack. If value is not null , the unsigned branchbyte1 and branchbyte2 are used to construct a signed 16-bit offset, where the offset is calculated to be ( branchbyte1 << 8) | branchbyte2 . Execution then proceeds at that offset from the address of the opcode of this ifnonnull instruction. The target address must be that of an opcode of an instruction within the method that contains this ifnonnull instruction.

Otherwise, execution proceeds at the address of the instruction following this ifnonnull instruction.

Branch if reference is null

ifnull branchbyte1 branchbyte2

ifnull = 198 (0xc6)

The value must of type reference . It is popped from the operand stack. If value is null , the unsigned branchbyte1 and branchbyte2 are used to construct a signed 16-bit offset, where the offset is calculated to be ( branchbyte1 << 8) | branchbyte2 . Execution then proceeds at that offset from the address of the opcode of this ifnull instruction. The target address must be that of an opcode of an instruction within the method that contains this ifnull instruction.

Otherwise, execution proceeds at the address of the instruction following this ifnull instruction.

Increment local variable by constant

iinc index const

iinc = 132 (0x84)

The index is an unsigned byte that must be an index into the local variable array of the current frame ( §2.6 ). The const is an immediate signed byte. The local variable at index must contain an int . The value const is first sign-extended to an int , and then the local variable at index is incremented by that amount.

The iinc opcode can be used in conjunction with the wide instruction ( § wide ) to access a local variable using a two-byte unsigned index and to increment it by a two-byte immediate signed value.

Load int from local variable

iload index

iload = 21 (0x15)

The index is an unsigned byte that must be an index into the local variable array of the current frame ( §2.6 ). The local variable at index must contain an int . The value of the local variable at index is pushed onto the operand stack.

The iload opcode can be used in conjunction with the wide instruction ( § wide ) to access a local variable using a two-byte unsigned index.

iload_<n>

iload_0 = 26 (0x1a)

iload_1 = 27 (0x1b)

iload_2 = 28 (0x1c)

iload_3 = 29 (0x1d)

The < n > must be an index into the local variable array of the current frame ( §2.6 ). The local variable at < n > must contain an int . The value of the local variable at < n > is pushed onto the operand stack.

Each of the iload_<n> instructions is the same as iload with an index of < n >, except that the operand < n > is implicit.

Multiply int

imul = 104 (0x68)

Both value1 and value2 must be of type int . The values are popped from the operand stack. The int result is value1 * value2 . The result is pushed onto the operand stack.

Despite the fact that overflow may occur, execution of an imul instruction never throws a run-time exception.

ineg = 116 (0x74)

The value must be of type int . It is popped from the operand stack. The int result is the arithmetic negation of value , - value . The result is pushed onto the operand stack.

For int values, negation is the same as subtraction from zero. Because the Java Virtual Machine uses two's-complement representation for integers and the range of two's-complement values is not symmetric, the negation of the maximum negative int results in that same maximum negative number. Despite the fact that overflow has occurred, no exception is thrown.

For all int values x , -x equals (~x)+1 .

Determine if object is of given type

instanceof indexbyte1 indexbyte2

instanceof = 193 (0xc1)

The objectref , which must be of type reference , is popped from the operand stack. The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class ( §2.6 ), where the value of the index is ( indexbyte1 << 8) | indexbyte2 . The run-time constant pool item at the index must be a symbolic reference to a class, array, or interface type.

If objectref is null , the instanceof instruction pushes an int result of 0 as an int on the operand stack.

Otherwise, the named class, array, or interface type is resolved ( §5.4.3.1 ). If objectref is an instance of the resolved class or array or implements the resolved interface, the instanceof instruction pushes an int result of 1 as an int on the operand stack; otherwise, it pushes an int result of 0.

The following rules are used to determine whether an objectref that is not null is an instance of the resolved type: If S is the class of the object referred to by objectref and T is the resolved class, array, or interface type, instanceof determines whether objectref is an instance of T as follows:

TC and SC are reference types, and type SC can be cast to TC by these run-time rules.

The instanceof instruction is very similar to the checkcast instruction ( § checkcast ). It differs in its treatment of null , its behavior when its test fails ( checkcast throws an exception, instanceof pushes a result code), and its effect on the operand stack.

invokedynamic

Invoke dynamic method

invokedynamic indexbyte1 indexbyte2 0 0

invokedynamic = 186 (0xba)

..., [ arg1 , [ arg2 ...]] →

Each specific lexical occurrence of an invokedynamic instruction is called a dynamic call site .

First, the unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class ( §2.6 ), where the value of the index is ( indexbyte1 << 8) | indexbyte2 . The run-time constant pool item at that index must be a symbolic reference to a call site specifier ( §5.1 ). The values of the third and fourth operand bytes must always be zero.

The call site specifier is resolved ( §5.4.3.6 ) for this specific dynamic call site to obtain a reference to a java.lang.invoke.MethodHandle instance, a reference to a java.lang.invoke.MethodType instance, and reference s to static arguments.

Next, as part of the continuing resolution of the call site specifier, the bootstrap method is invoked as if by execution of an invokevirtual instruction ( § invokevirtual ) that contains a run-time constant pool index to a symbolic reference to a method ( §5.1 ) with the following properties:

The method's name is invoke ;

The method's descriptor has a return type of java.lang.invoke.CallSite ;

The method's descriptor has parameter types derived from the items pushed on to the operand stack, as follows.

The first four parameter types in the descriptor are java.lang.invoke.MethodHandle , java.lang.invoke.MethodHandles.Lookup , String , and java.lang.invoke.MethodType , in that order.

If the call site specifier has any static arguments, then a parameter type for each argument is appended to the parameter types of the method descriptor in the order that the arguments were pushed on to the operand stack. These parameter types may be Class , java.lang.invoke.MethodHandle , java.lang.invoke.MethodType , String , int , long , float , or double .

The method's symbolic reference to the class in which the method is to be found indicates the class java.lang.invoke.MethodHandle .

where it is as if the following items were pushed, in order, onto the operand stack:

the reference to the java.lang.invoke.MethodHandle object for the bootstrap method;

a reference to a java.lang.invoke.MethodHandles.Lookup object for the class in which this dynamic call site occurs;

a reference to the String for the method name in the call site specifier;

the reference to the java.lang.invoke.MethodType object obtained for the method descriptor in the call site specifier;

reference s to classes, method types, method handles, and string literals denoted as static arguments in the call site specifier, and numeric values ( §2.3.1 , §2.3.2 ) denoted as static arguments in the call site specifier, in the order in which they appear in the call site specifier. (That is, no boxing occurs for primitive values.)

As long as the bootstrap method can be correctly invoked by the invoke method, its descriptor is arbitrary. For example, the first parameter type could be Object instead of java.lang.invoke.MethodHandles.Lookup , and the return type could also be Object instead of java.lang.invoke.CallSite .

If the bootstrap method is a variable arity method, then some or all of the arguments on the operand stack specified above may be collected into a trailing array parameter.

The invocation of a bootstrap method occurs within a thread that is attempting resolution of the symbolic reference to the call site specifier of this dynamic call site . If there are several such threads, the bootstrap method may be invoked in several threads concurrently. Therefore, bootstrap methods which access global application data must take the usual precautions against race conditions.

The result returned by the bootstrap method must be a reference to an object whose class is java.lang.invoke.CallSite or a subclass of java.lang.invoke.CallSite . This object is known as the call site object . The reference is popped from the operand stack used as if in the execution of an invokevirtual instruction.

If several threads simultaneously execute the bootstrap method for the same dynamic call site, the Java Virtual Machine must choose one returned call site object and install it visibly to all threads. Any other bootstrap methods executing for the dynamic call site are allowed to complete, but their results are ignored, and the threads' execution of the dynamic call site proceeds with the chosen call site object.

The call site object has a type descriptor (an instance of java.lang.invoke.MethodType ) which must be semantically equal to the java.lang.invoke.MethodType object obtained for the method descriptor in the call site specifier.

The result of successful call site specifier resolution is a call site object which is permanently bound to the dynamic call site.

The method handle represented by the target of the bound call site object is invoked. The invocation occurs as if by execution of an invokevirtual instruction ( § invokevirtual ) that indicates a run-time constant pool index to a symbolic reference to a method ( §5.1 ) with the following properties:

The method's name is invokeExact ;

The method's descriptor is the method descriptor in the call site specifier; and

The operand stack will be interpreted as containing a reference to the target of the call site object, followed by nargs argument values, where the number, type, and order of the values must be consistent with the method descriptor in the call site specifier.

If resolution of the symbolic reference to the call site specifier throws an exception E , the invokedynamic instruction throws a BootstrapMethodError that wraps E .

Otherwise, during the continuing resolution of the call site specifier, if invocation of the bootstrap method completes abruptly ( §2.6.5 ) because of a throw of exception E , the invokedynamic instruction throws a BootstrapMethodError that wraps E . (This can occur if the bootstrap method has the wrong arity, parameter type, or return type, causing java.lang.invoke.MethodHandle . invoke to throw java.lang.invoke.WrongMethodTypeException .)

Otherwise, during the continuing resolution of the call site specifier, if the result from the bootstrap method invocation is not a reference to an instance of java.lang.invoke.CallSite , the invokedynamic instruction throws a BootstrapMethodError .

Otherwise, during the continuing resolution of the call site specifier, if the type descriptor of the target of the call site object is not semantically equal to the method descriptor in the call site specifier, the invokedynamic instruction throws a BootstrapMethodError .

If this specific dynamic call site completed resolution of its call site specifier, it implies that a non- null reference to an instance of java.lang.invoke.CallSite is bound to this dynamic call site. Therefore, the operand stack item which represents a reference to the target of the call site object is never null . Similarly, it implies that the method descriptor in the call site specifier is semantically equal to the type descriptor of the method handle to be invoked as if by execution of an invokevirtual instruction.

These invariants mean that an invokedynamic instruction which is bound to a call site object never throws a NullPointerException or a java.lang.invoke.WrongMethodTypeException .

invokeinterface

Invoke interface method

invokeinterface indexbyte1 indexbyte2 count 0

invokeinterface = 185 (0xb9)

..., objectref , [ arg1 , [ arg2 ...]] →

The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class ( §2.6 ), where the value of the index is ( indexbyte1 << 8) | indexbyte2 . The run-time constant pool item at that index must be a symbolic reference to an interface method ( §5.1 ), which gives the name and descriptor ( §4.3.3 ) of the interface method as well as a symbolic reference to the interface in which the interface method is to be found. The named interface method is resolved ( §5.4.3.4 ). The resolved interface method must not be an instance initialization method ( §2.9 ) or the class or interface initialization method ( §2.9 ).

The count operand is an unsigned byte that must not be zero. The objectref must be of type reference and must be followed on the operand stack by nargs argument values, where the number, type, and order of the values must be consistent with the descriptor of the resolved interface method. The value of the fourth operand byte must always be zero.

Let C be the class of objectref . The actual method to be invoked is selected by the following lookup procedure:

If C contains a declaration for an instance method with the same name and descriptor as the resolved method, then this is the method to be invoked, and the lookup procedure terminates.

Otherwise, if C has a superclass, this same lookup procedure is performed recursively using the direct superclass of C ; the method to be invoked is the result of the recursive invocation of this lookup procedure.

Otherwise, an AbstractMethodError is raised.

If the method is synchronized , the monitor associated with objectref is entered or reentered as if by execution of a monitorenter instruction ( § monitorenter ) in the current thread.

If the method is not native , the nargs argument values and objectref are popped from the operand stack. A new frame is created on the Java Virtual Machine stack for the method being invoked. The objectref and the argument values are consecutively made the values of local variables of the new frame, with objectref in local variable 0, arg1 in local variable 1 (or, if arg1 is of type long or double , in local variables 1 and 2), and so on. Any argument value that is of a floating-point type undergoes value set conversion ( §2.8.3 ) prior to being stored in a local variable. The new frame is then made current, and the Java Virtual Machine pc is set to the opcode of the first instruction of the method to be invoked. Execution continues with the first instruction of the method.

If the method is native and the platform-dependent code that implements it has not yet been bound ( §5.6 ) into the Java Virtual Machine, that is done. The nargs argument values and objectref are popped from the operand stack and are passed as parameters to the code that implements the method. Any argument value that is of a floating-point type undergoes value set conversion ( §2.8.3 ) prior to being passed as a parameter. The parameters are passed and the code is invoked in an implementation-dependent manner. When the platform-dependent code returns:

If the native method is synchronized , the monitor associated with objectref is updated and possibly exited as if by execution of a monitorexit instruction ( § monitorexit ) in the current thread.

If the native method returns a value, the return value of the platform-dependent code is converted in an implementation-dependent way to the return type of the native method and pushed onto the operand stack.

During resolution of the symbolic reference to the interface method, any of the exceptions pertaining to interface method resolution ( §5.4.3.4 ) can be thrown.

Otherwise, if objectref is null , the invokeinterface instruction throws a NullPointerException .

Otherwise, if the class of objectref does not implement the resolved interface, invokeinterface throws an IncompatibleClassChangeError .

Otherwise, if no method matching the resolved name and descriptor is selected, invokeinterface throws an AbstractMethodError .

Otherwise, if the selected method is not public , invokeinterface throws an IllegalAccessError .

Otherwise, if the selected method is abstract , invokeinterface throws an AbstractMethodError .

Otherwise, if the selected method is native and the code that implements the method cannot be bound, invokeinterface throws an UnsatisfiedLinkError .

The count operand of the invokeinterface instruction records a measure of the number of argument values, where an argument value of type long or type double contributes two units to the count value and an argument of any other type contributes one unit. This information can also be derived from the descriptor of the selected method. The redundancy is historical.

The fourth operand byte exists to reserve space for an additional operand used in certain of Oracle's Java Virtual Machine implementations, which replace the invokeinterface instruction by a specialized pseudo-instruction at run time. It must be retained for backwards compatibility.

The nargs argument values and objectref are not one-to-one with the first nargs +1 local variables. Argument values of types long and double must be stored in two consecutive local variables, thus more than nargs local variables may be required to pass nargs argument values to the invoked method.

invokespecial

Invoke instance method; special handling for superclass, private, and instance initialization method invocations

invokespecial indexbyte1 indexbyte2

invokespecial = 183 (0xb7)

The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class ( §2.6 ), where the value of the index is ( indexbyte1 << 8) | indexbyte2 . The run-time constant pool item at that index must be a symbolic reference to a method ( §5.1 ), which gives the name and descriptor ( §4.3.3 ) of the method as well as a symbolic reference to the class in which the method is to be found. The named method is resolved ( §5.4.3.3 ). Finally, if the resolved method is protected ( §4.6 ), and it is a member of a superclass of the current class, and the method is not declared in the same run-time package ( §5.3 ) as the current class, then the class of objectref must be either the current class or a subclass of the current class.

Next, the resolved method is selected for invocation unless all of the following conditions are true:

The ACC_SUPER flag ( Table 4.1 ) is set for the current class.

The class of the resolved method is a superclass of the current class.

The resolved method is not an instance initialization method ( §2.9 ).

If the above conditions are true, the actual method to be invoked is selected by the following lookup procedure. Let C be the direct superclass of the current class:

If C contains a declaration for an instance method with the same name and descriptor as the resolved method, then this method will be invoked. The lookup procedure terminates.

Otherwise, if C has a superclass, this same lookup procedure is performed recursively using the direct superclass of C . The method to be invoked is the result of the recursive invocation of this lookup procedure.

The objectref must be of type reference and must be followed on the operand stack by nargs argument values, where the number, type, and order of the values must be consistent with the descriptor of the selected instance method.

If the method is native and the platform-dependent code that implements it has not yet been bound ( §5.6 ) into the Java Virtual Machine, that is done. The nargs argument values and objectref are popped from the operand stack and are passed as parameters to the code that implements the method. Any argument value that is of a floating-point type undergoes value set conversion ( §2.8.3 ) prior to being passed as a parameter. The parameters are passed and the code is invoked in an implementation-dependent manner. When the platform-dependent code returns, the following take place:

During resolution of the symbolic reference to the method, any of the exceptions pertaining to method resolution ( §5.4.3.3 ) can be thrown.

Otherwise, if the resolved method is an instance initialization method, and the class in which it is declared is not the class symbolically referenced by the instruction, a NoSuchMethodError is thrown.

Otherwise, if the resolved method is a class ( static ) method, the invokespecial instruction throws an IncompatibleClassChangeError .

Otherwise, if objectref is null , the invokespecial instruction throws a NullPointerException .

Otherwise, if no method matching the resolved name and descriptor is selected, invokespecial throws an AbstractMethodError .

Otherwise, if the selected method is abstract , invokespecial throws an AbstractMethodError .

Otherwise, if the selected method is native and the code that implements the method cannot be bound, invokespecial throws an UnsatisfiedLinkError .

The difference between the invokespecial instruction and the invokevirtual instruction ( § invokevirtual ) is that invokevirtual invokes a method based on the class of the object. The invokespecial instruction is used to invoke instance initialization methods ( §2.9 ) as well as private methods and methods of a superclass of the current class.

The invokespecial instruction was named invokenonvirtual prior to JDK release 1.0.2.

invokestatic

Invoke a class ( static ) method

invokestatic indexbyte1 indexbyte2

invokestatic = 184 (0xb8)

The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class ( §2.6 ), where the value of the index is ( indexbyte1 << 8) | indexbyte2 . The run-time constant pool item at that index must be a symbolic reference to a method ( §5.1 ), which gives the name and descriptor ( §4.3.3 ) of the method as well as a symbolic reference to the class in which the method is to be found. The named method is resolved ( §5.4.3.3 ). The resolved method must not be an instance initialization method ( §2.9 ) or the class or interface initialization method ( §2.9 ). It must be static , and therefore cannot be abstract .

On successful resolution of the method, the class that declared the resolved method is initialized ( §5.5 ) if that class has not already been initialized.

The operand stack must contain nargs argument values, where the number, type, and order of the values must be consistent with the descriptor of the resolved method.

If the method is synchronized , the monitor associated with the resolved Class object is entered or reentered as if by execution of a monitorenter instruction ( § monitorenter ) in the current thread.

If the method is not native , the nargs argument values are popped from the operand stack. A new frame is created on the Java Virtual Machine stack for the method being invoked. The nargs argument values are consecutively made the values of local variables of the new frame, with arg1 in local variable 0 (or, if arg1 is of type long or double , in local variables 0 and 1) and so on. Any argument value that is of a floating-point type undergoes value set conversion ( §2.8.3 ) prior to being stored in a local variable. The new frame is then made current, and the Java Virtual Machine pc is set to the opcode of the first instruction of the method to be invoked. Execution continues with the first instruction of the method.

If the method is native and the platform-dependent code that implements it has not yet been bound ( §5.6 ) into the Java Virtual Machine, that is done. The nargs argument values are popped from the operand stack and are passed as parameters to the code that implements the method. Any argument value that is of a floating-point type undergoes value set conversion ( §2.8.3 ) prior to being passed as a parameter. The parameters are passed and the code is invoked in an implementation-dependent manner. When the platform-dependent code returns, the following take place:

If the native method is synchronized , the monitor associated with the resolved Class object is updated and possibly exited as if by execution of a monitorexit instruction ( § monitorexit ) in the current thread.

Otherwise, if the resolved method is an instance method, the invokestatic instruction throws an IncompatibleClassChangeError .

Otherwise, if execution of this invokestatic instruction causes initialization of the referenced class, invokestatic may throw an Error as detailed in §5.5 .

Otherwise, if the resolved method is native and the code that implements the method cannot be bound, invokestatic throws an UnsatisfiedLinkError .

The nargs argument values are not one-to-one with the first nargs local variables. Argument values of types long and double must be stored in two consecutive local variables, thus more than nargs local variables may be required to pass nargs argument values to the invoked method.

invokevirtual

Invoke instance method; dispatch based on class

invokevirtual indexbyte1 indexbyte2

invokevirtual = 182 (0xb6)

The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class ( §2.6 ), where the value of the index is ( indexbyte1 << 8) | indexbyte2 . The run-time constant pool item at that index must be a symbolic reference to a method ( §5.1 ), which gives the name and descriptor ( §4.3.3 ) of the method as well as a symbolic reference to the class in which the method is to be found. The named method is resolved ( §5.4.3.3 ). The resolved method must not be an instance initialization method ( §2.9 ) or the class or interface initialization method ( §2.9 ). Finally, if the resolved method is protected ( §4.6 ), and it is a member of a superclass of the current class, and the method is not declared in the same run-time package ( §5.3 ) as the current class, then the class of objectref must be either the current class or a subclass of the current class.

If the resolved method is not signature polymorphic ( §2.9 ), then the invokevirtual instruction proceeds as follows.

If C contains a declaration for an instance method m that overrides ( §5.4.5 ) the resolved method, then m is the method to be invoked, and the lookup procedure terminates.

The objectref must be followed on the operand stack by nargs argument values, where the number, type, and order of the values must be consistent with the descriptor of the selected instance method.

If the resolved method is signature polymorphic ( §2.9 ), then the invokevirtual instruction proceeds as follows.

First, a reference to an instance of java.lang.invoke.MethodType is obtained as if by resolution of a symbolic reference to a method type ( §5.4.3.5 ) with the same parameter and return types as the descriptor of the method referenced by the invokevirtual instruction.

If the named method is invokeExact , the instance of java.lang.invoke.MethodType must be semantically equal to the type descriptor of the receiving method handle objectref . The method handle to be invoked is objectref .

If the named method is invoke , and the instance of java.lang.invoke.MethodType is semantically equal to the type descriptor of the receiving method handle objectref , then the method handle to be invoked is objectref .

If the named method is invoke , and the instance of java.lang.invoke.MethodType is not semantically equal to the type descriptor of the receiving method handle objectref , then the Java Virtual Machine attempts to adjust the type descriptor of the receiving method handle, as if by a call to java.lang.invoke.MethodHandle.asType , to obtain an exactly invokable method handle m . The method handle to be invoked is m .

The objectref must be followed on the operand stack by nargs argument values, where the number, type, and order of the values must be consistent with the type descriptor of the method handle to be invoked. (This type descriptor will correspond to the method descriptor appropriate for the kind of the method handle to be invoked, as specified in §5.4.3.5 .)

Then, if the method handle to be invoked has bytecode behavior, the Java Virtual Machine invokes the method handle as if by execution of the bytecode behavior associated with the method handle's kind. If the kind is 5 ( REF_invokeVirtual ), 6 ( REF_invokeStatic ), 7 ( REF_invokeSpecial ), 8 ( REF_newInvokeSpecial ), or 9 ( REF_invokeInterface ), then a frame will be created and made current in the course of executing the bytecode behavior ; when the method invoked by the bytecode behavior completes (normally or abruptly), the frame of its invoker is considered to be the frame for the method containing this invokevirtual instruction.

The frame in which the bytecode behavior itself executes is not visible.

Otherwise, if the method handle to be invoked has no bytecode behavior, the Java Virtual Machine invokes it in an implementation-dependent manner.

Otherwise, if the resolved method is a class ( static ) method, the invokevirtual instruction throws an IncompatibleClassChangeError .

Otherwise, if the resolved method is signature polymorphic, then during resolution of the method type derived from the descriptor in the symbolic reference to the method, any of the exceptions pertaining to method type resolution ( §5.4.3.5 ) can be thrown.

Otherwise, if objectref is null , the invokevirtual instruction throws a NullPointerException .

Otherwise, if the resolved method is not signature polymorphic:

If no method matching the resolved name and descriptor is selected, invokevirtual throws an AbstractMethodError .

Otherwise, if the selected method is abstract , invokevirtual throws an AbstractMethodError .

Otherwise, if the selected method is native and the code that implements the method cannot be bound, invokevirtual throws an UnsatisfiedLinkError .

Otherwise, if the resolved method is signature polymorphic, then:

If the method name is invokeExact , and the obtained instance of java.lang.invoke.MethodType is not semantically equal to the type descriptor of the receiving method handle, the invokevirtual instruction throws a java.lang.invoke.WrongMethodTypeException .

If the method name is invoke , and the obtained instance of java.lang.invoke.MethodType is not a valid argument to the java.lang.invoke.MethodHandle.asType method invoked on the receiving method handle, the invokevirtual instruction throws a java.lang.invoke.WrongMethodTypeException .

Boolean OR int

ior = 128 (0x80)

Both value1 and value2 must be of type int . They are popped from the operand stack. An int result is calculated by taking the bitwise inclusive OR of value1 and value2 . The result is pushed onto the operand stack.

Remainder int

irem = 112 (0x70)

Both value1 and value2 must be of type int . The values are popped from the operand stack. The int result is value1 - ( value1 / value2 ) * value2 . The result is pushed onto the operand stack.

The result of the irem instruction is such that (a/b)*b + (a%b) is equal to a . This identity holds even in the special case in which the dividend is the negative int of largest possible magnitude for its type and the divisor is -1 (the remainder is 0). It follows from this rule that the result of the remainder operation can be negative only if the dividend is negative and can be positive only if the dividend is positive. Moreover, the magnitude of the result is always less than the magnitude of the divisor.

If the value of the divisor for an int remainder operator is 0, irem throws an ArithmeticException .

Return int from method

ireturn = 172 (0xac)

The current method must have return type boolean , byte , short , char , or int . The value must be of type int . If the current method is a synchronized method, the monitor entered or reentered on invocation of the method is updated and possibly exited as if by execution of a monitorexit instruction ( § monitorexit ) in the current thread. If no exception is thrown, value is popped from the operand stack of the current frame ( §2.6 ) and pushed onto the operand stack of the frame of the invoker. Any other values on the operand stack of the current method are discarded.

If the Java Virtual Machine implementation does not enforce the rules on structured locking described in §2.11.10 , then if the current method is a synchronized method and the current thread is not the owner of the monitor entered or reentered on invocation of the method, ireturn throws an IllegalMonitorStateException . This can happen, for example, if a synchronized method contains a monitorexit instruction, but no monitorenter instruction, on the object on which the method is synchronized.

Otherwise, if the Java Virtual Machine implementation enforces the rules on structured locking described in §2.11.10 and if the first of those rules is violated during invocation of the current method, then ireturn throws an IllegalMonitorStateException .

Shift left int

ishl = 120 (0x78)

Both value1 and value2 must be of type int . The values are popped from the operand stack. An int result is calculated by shifting value1 left by s bit positions, where s is the value of the low 5 bits of value2 . The result is pushed onto the operand stack.

This is equivalent (even if overflow occurs) to multiplication by 2 to the power s . The shift distance actually used is always in the range 0 to 31, inclusive, as if value2 were subjected to a bitwise logical AND with the mask value 0x1f.

Arithmetic shift right int

ishr = 122 (0x7a)

Both value1 and value2 must be of type int . The values are popped from the operand stack. An int result is calculated by shifting value1 right by s bit positions, with sign extension, where s is the value of the low 5 bits of value2 . The result is pushed onto the operand stack.

The resulting value is ⌊ value1 / 2 s ⌋, where s is value2 & 0x1f. For non-negative value1 , this is equivalent to truncating int division by 2 to the power s . The shift distance actually used is always in the range 0 to 31, inclusive, as if value2 were subjected to a bitwise logical AND with the mask value 0x1f.

Store int into local variable

istore index

istore = 54 (0x36)

The index is an unsigned byte that must be an index into the local variable array of the current frame ( §2.6 ). The value on the top of the operand stack must be of type int . It is popped from the operand stack, and the value of the local variable at index is set to value .

The istore opcode can be used in conjunction with the wide instruction ( § wide ) to access a local variable using a two-byte unsigned index.

istore_<n>

istore_0 = 59 (0x3b)

istore_1 = 60 (0x3c)

istore_2 = 61 (0x3d)

istore_3 = 62 (0x3e)

The < n > must be an index into the local variable array of the current frame ( §2.6 ). The value on the top of the operand stack must be of type int . It is popped from the operand stack, and the value of the local variable at < n > is set to value .

Each of the istore_<n> instructions is the same as istore with an index of < n >, except that the operand < n > is implicit.

Subtract int

isub = 100 (0x64)

Both value1 and value2 must be of type int . The values are popped from the operand stack. The int result is value1 - value2 . The result is pushed onto the operand stack.

For int subtraction, a-b produces the same result as a+(-b) . For int values, subtraction from zero is the same as negation.

The result is the 32 low-order bits of the true mathematical result in a sufficiently wide two's-complement format, represented as a value of type int . If overflow occurs, then the sign of the result may not be the same as the sign of the mathematical difference of the two values.

Despite the fact that overflow may occur, execution of an isub instruction never throws a run-time exception.

Logical shift right int

iushr = 124 (0x7c)

Both value1 and value2 must be of type int . The values are popped from the operand stack. An int result is calculated by shifting value1 right by s bit positions, with zero extension, where s is the value of the low 5 bits of value2 . The result is pushed onto the operand stack.

If value1 is positive and s is value2 & 0x1f, the result is the same as that of value1 >> s ; if value1 is negative, the result is equal to the value of the expression ( value1 >> s ) + (2 << ~ s ). The addition of the (2 << ~ s ) term cancels out the propagated sign bit. The shift distance actually used is always in the range 0 to 31, inclusive.

Boolean XOR int

ixor = 130 (0x82)

Both value1 and value2 must be of type int . They are popped from the operand stack. An int result is calculated by taking the bitwise exclusive OR of value1 and value2 . The result is pushed onto the operand stack.

Jump subroutine

jsr branchbyte1 branchbyte2

jsr = 168 (0xa8)

..., address

The address of the opcode of the instruction immediately following this jsr instruction is pushed onto the operand stack as a value of type returnAddress . The unsigned branchbyte1 and branchbyte2 are used to construct a signed 16-bit offset, where the offset is ( branchbyte1 << 8) | branchbyte2 . Execution proceeds at that offset from the address of this jsr instruction. The target address must be that of an opcode of an instruction within the method that contains this jsr instruction.

Note that jsr pushes the address onto the operand stack and ret ( § ret ) gets it out of a local variable. This asymmetry is intentional.

In Oracle's implementation of a compiler for the Java programming language prior to Java SE 6, the jsr instruction was used with the ret instruction in the implementation of the finally clause ( §3.13 , §4.10.2.5 ).

Jump subroutine (wide index)

jsr_w branchbyte1 branchbyte2 branchbyte3 branchbyte4

jsr_w = 201 (0xc9)

The address of the opcode of the instruction immediately following this jsr_w instruction is pushed onto the operand stack as a value of type returnAddress . The unsigned branchbyte1 , branchbyte2 , branchbyte3 , and branchbyte4 are used to construct a signed 32-bit offset, where the offset is ( branchbyte1 << 24) | ( branchbyte2 << 16) | ( branchbyte3 << 8) | branchbyte4 . Execution proceeds at that offset from the address of this jsr_w instruction. The target address must be that of an opcode of an instruction within the method that contains this jsr_w instruction.

Note that jsr_w pushes the address onto the operand stack and ret ( § ret ) gets it out of a local variable. This asymmetry is intentional.

In Oracle's implementation of a compiler for the Java programming language prior to Java SE 6, the jsr_w instruction was used with the ret instruction in the implementation of the finally clause ( §3.13 , §4.10.2.5 ).

Although the jsr_w instruction takes a 4-byte branch offset, other factors limit the size of a method to 65535 bytes ( §4.11 ). This limit may be raised in a future release of the Java Virtual Machine.

Convert long to double

l2d = 138 (0x8a)

The value on the top of the operand stack must be of type long . It is popped from the operand stack and converted to a double result using IEEE 754 round to nearest mode. The result is pushed onto the operand stack.

The l2d instruction performs a widening primitive conversion (JLS §5.1.2) that may lose precision because values of type double have only 53 significand bits.

Convert long to float

l2f = 137 (0x89)

The value on the top of the operand stack must be of type long . It is popped from the operand stack and converted to a float result using IEEE 754 round to nearest mode. The result is pushed onto the operand stack.

The l2f instruction performs a widening primitive conversion (JLS §5.1.2) that may lose precision because values of type float have only 24 significand bits.

Convert long to int

l2i = 136 (0x88)

The value on the top of the operand stack must be of type long . It is popped from the operand stack and converted to an int result by taking the low-order 32 bits of the long value and discarding the high-order 32 bits. The result is pushed onto the operand stack.

The l2i instruction performs a narrowing primitive conversion (JLS §5.1.3). It may lose information about the overall magnitude of value . The result may also not have the same sign as value.

ladd = 97 (0x61)

Both value1 and value2 must be of type long . The values are popped from the operand stack. The long result is value1 + value2 . The result is pushed onto the operand stack.

The result is the 64 low-order bits of the true mathematical result in a sufficiently wide two's-complement format, represented as a value of type long . If overflow occurs, the sign of the result may not be the same as the sign of the mathematical sum of the two values.

Despite the fact that overflow may occur, execution of an ladd instruction never throws a run-time exception.

Load long from array

laload = 47 (0x2f)

The arrayref must be of type reference and must refer to an array whose components are of type long . The index must be of type int . Both arrayref and index are popped from the operand stack. The long value in the component of the array at index is retrieved and pushed onto the operand stack.

If arrayref is null , laload throws a NullPointerException .

Otherwise, if index is not within the bounds of the array referenced by arrayref , the laload instruction throws an ArrayIndexOutOfBoundsException .

Boolean AND long

land = 127 (0x7f)

Both value1 and value2 must be of type long . They are popped from the operand stack. A long result is calculated by taking the bitwise AND of value1 and value2 . The result is pushed onto the operand stack.

Store into long array

lastore = 80 (0x50)

The arrayref must be of type reference and must refer to an array whose components are of type long . The index must be of type int , and value must be of type long . The arrayref , index , and value are popped from the operand stack. The long value is stored as the component of the array indexed by index .

If arrayref is null , lastore throws a NullPointerException .

Otherwise, if index is not within the bounds of the array referenced by arrayref , the lastore instruction throws an ArrayIndexOutOfBoundsException .

Compare long

lcmp = 148 (0x94)

Both value1 and value2 must be of type long . They are both popped from the operand stack, and a signed integer comparison is performed. If value1 is greater than value2 , the int value 1 is pushed onto the operand stack. If value1 is equal to value2 , the int value 0 is pushed onto the operand stack. If value1 is less than value2 , the int value -1 is pushed onto the operand stack.

lconst_<l>

Push long constant

..., < l >

Push the long constant < l > (0 or 1) onto the operand stack.

Push item from run-time constant pool

ldc = 18 (0x12)

The index is an unsigned byte that must be a valid index into the run-time constant pool of the current class ( §2.6 ). The run-time constant pool entry at index either must be a run-time constant of type int or float , or a reference to a string literal, or a symbolic reference to a class, method type, or method handle ( §5.1 ).

If the run-time constant pool entry is a run-time constant of type int or float , the numeric value of that run-time constant is pushed onto the operand stack as an int or float , respectively.

Otherwise, if the run-time constant pool entry is a reference to an instance of class String representing a string literal ( §5.1 ), then a reference to that instance, value , is pushed onto the operand stack.

Otherwise, if the run-time constant pool entry is a symbolic reference to a class ( §5.1 ), then the named class is resolved ( §5.4.3.1 ) and a reference to the Class object representing that class, value , is pushed onto the operand stack.

Otherwise, the run-time constant pool entry must be a symbolic reference to a method type or a method handle ( §5.1 ). The method type or method handle is resolved ( §5.4.3.5 ) and a reference to the resulting instance of java.lang.invoke.MethodType or java.lang.invoke.MethodHandle , value , is pushed onto the operand stack.

During resolution of a symbolic reference to a class, any of the exceptions pertaining to class resolution ( §5.4.3.1 ) can be thrown.

During resolution of a symbolic reference to a method type or method handle, any of the exception pertaining to method type or method handle resolution ( §5.4.3.5 ) can be thrown.

The ldc instruction can only be used to push a value of type float taken from the float value set ( §2.3.2 ) because a constant of type float in the constant pool ( §4.4.4 ) must be taken from the float value set.

Push item from run-time constant pool (wide index)

ldc_w indexbyte1 indexbyte2

ldc_w = 19 (0x13)

The unsigned indexbyte1 and indexbyte2 are assembled into an unsigned 16-bit index into the run-time constant pool of the current class ( §2.6 ), where the value of the index is calculated as ( indexbyte1 << 8) | indexbyte2 . The index must be a valid index into the run-time constant pool of the current class. The run-time constant pool entry at the index either must be a run-time constant of type int or float , or a reference to a string literal, or a symbolic reference to a class, method type, or method handle ( §5.1 ).

Otherwise, if the run-time constant pool entry is a symbolic reference to a class ( §4.4.1 ). The named class is resolved ( §5.4.3.1 ) and a reference to the Class object representing that class, value , is pushed onto the operand stack.

During resolution of the symbolic reference to a class, any of the exceptions pertaining to class resolution ( §5.4.3.1 ) can be thrown.

The ldc_w instruction is identical to the ldc instruction ( § ldc ) except for its wider run-time constant pool index.

The ldc_w instruction can only be used to push a value of type float taken from the float value set ( §2.3.2 ) because a constant of type float in the constant pool ( §4.4.4 ) must be taken from the float value set.

Push long or double from run-time constant pool (wide index)

ldc2_w indexbyte1 indexbyte2

ldc2_w = 20 (0x14)

The unsigned indexbyte1 and indexbyte2 are assembled into an unsigned 16-bit index into the run-time constant pool of the current class ( §2.6 ), where the value of the index is calculated as ( indexbyte1 << 8) | indexbyte2 . The index must be a valid index into the run-time constant pool of the current class. The run-time constant pool entry at the index must be a run-time constant of type long or double ( §5.1 ). The numeric value of that run-time constant is pushed onto the operand stack as a long or double , respectively.

Only a wide-index version of the ldc2_w instruction exists; there is no ldc2 instruction that pushes a long or double with a single-byte index.

The ldc2_w instruction can only be used to push a value of type double taken from the double value set ( §2.3.2 ) because a constant of type double in the constant pool ( §4.4.5 ) must be taken from the double value set.

Divide long

ldiv = 109 (0x6d)

Both value1 and value2 must be of type long . The values are popped from the operand stack. The long result is the value of the Java programming language expression value1 / value2 . The result is pushed onto the operand stack.

A long division rounds towards 0; that is, the quotient produced for long values in n / d is a long value q whose magnitude is as large as possible while satisfying | d · q | ≤ | n |. Moreover, q is positive when | n | ≥ | d | and n and d have the same sign, but q is negative when | n | ≥ | d | and n and d have opposite signs.

There is one special case that does not satisfy this rule: if the dividend is the negative integer of largest possible magnitude for the long type and the divisor is -1, then overflow occurs and the result is equal to the dividend; despite the overflow, no exception is thrown in this case.

If the value of the divisor in a long division is 0, ldiv throws an ArithmeticException .

Load long from local variable

lload index

lload = 22 (0x16)

The index is an unsigned byte. Both index and index +1 must be indices into the local variable array of the current frame ( §2.6 ). The local variable at index must contain a long . The value of the local variable at index is pushed onto the operand stack.

The lload opcode can be used in conjunction with the wide instruction ( § wide ) to access a local variable using a two-byte unsigned index.

lload_<n>

lload_0 = 30 (0x1e)

lload_1 = 31 (0x1f)

lload_2 = 32 (0x20)

lload_3 = 33 (0x21)

Both < n > and < n >+1 must be indices into the local variable array of the current frame ( §2.6 ). The local variable at < n > must contain a long . The value of the local variable at < n > is pushed onto the operand stack.

Each of the lload_<n> instructions is the same as lload with an index of < n >, except that the operand < n > is implicit.

Multiply long

lmul = 105 (0x69)

Both value1 and value2 must be of type long . The values are popped from the operand stack. The long result is value1 * value2 . The result is pushed onto the operand stack.

Despite the fact that overflow may occur, execution of an lmul instruction never throws a run-time exception.

Negate long

lneg = 117 (0x75)

The value must be of type long . It is popped from the operand stack. The long result is the arithmetic negation of value , - value . The result is pushed onto the operand stack.

For long values, negation is the same as subtraction from zero. Because the Java Virtual Machine uses two's-complement representation for integers and the range of two's-complement values is not symmetric, the negation of the maximum negative long results in that same maximum negative number. Despite the fact that overflow has occurred, no exception is thrown.

For all long values x , -x equals (~x)+1 .

lookupswitch

Access jump table by key match and jump

lookupswitch <0-3 byte pad> defaultbyte1 defaultbyte2 defaultbyte3 defaultbyte4 npairs1 npairs2 npairs3 npairs4 match-offset pairs...

lookupswitch = 171 (0xab)

..., key →

A lookupswitch is a variable-length instruction. Immediately after the lookupswitch opcode, between zero and three bytes must act as padding, such that defaultbyte1 begins at an address that is a multiple of four bytes from the start of the current method (the opcode of its first instruction). Immediately after the padding follow a series of signed 32-bit values: default , npairs , and then npairs pairs of signed 32-bit values. The npairs must be greater than or equal to 0. Each of the npairs pairs consists of an int match and a signed 32-bit offset . Each of these signed 32-bit values is constructed from four unsigned bytes as ( byte1 << 24) | ( byte2 << 16) | ( byte3 << 8) | byte4 .

The table match-offset pairs of the lookupswitch instruction must be sorted in increasing numerical order by match .

The key must be of type int and is popped from the operand stack. The key is compared against the match values. If it is equal to one of them, then a target address is calculated by adding the corresponding offset to the address of the opcode of this lookupswitch instruction. If the key does not match any of the match values, the target address is calculated by adding default to the address of the opcode of this lookupswitch instruction. Execution then continues at the target address.

The target address that can be calculated from the offset of each match-offset pair, as well as the one calculated from default , must be the address of an opcode of an instruction within the method that contains this lookupswitch instruction.

The alignment required of the 4-byte operands of the lookupswitch instruction guarantees 4-byte alignment of those operands if and only if the method that contains the lookupswitch is positioned on a 4-byte boundary.

The match-offset pairs are sorted to support lookup routines that are quicker than linear search.

Boolean OR long

lor = 129 (0x81)

Both value1 and value2 must be of type long . They are popped from the operand stack. A long result is calculated by taking the bitwise inclusive OR of value1 and value2 . The result is pushed onto the operand stack.

Remainder long

lrem = 113 (0x71)

Both value1 and value2 must be of type long . The values are popped from the operand stack. The long result is value1 - ( value1 / value2 ) * value2 . The result is pushed onto the operand stack.

The result of the lrem instruction is such that (a/b)*b + (a%b) is equal to a . This identity holds even in the special case in which the dividend is the negative long of largest possible magnitude for its type and the divisor is -1 (the remainder is 0). It follows from this rule that the result of the remainder operation can be negative only if the dividend is negative and can be positive only if the dividend is positive; moreover, the magnitude of the result is always less than the magnitude of the divisor.

If the value of the divisor for a long remainder operator is 0, lrem throws an ArithmeticException .

Return long from method

lreturn = 173 (0xad)

The current method must have return type long . The value must be of type long . If the current method is a synchronized method, the monitor entered or reentered on invocation of the method is updated and possibly exited as if by execution of a monitorexit instruction ( § monitorexit ) in the current thread. If no exception is thrown, value is popped from the operand stack of the current frame ( §2.6 ) and pushed onto the operand stack of the frame of the invoker. Any other values on the operand stack of the current method are discarded.

If the Java Virtual Machine implementation does not enforce the rules on structured locking described in §2.11.10 , then if the current method is a synchronized method and the current thread is not the owner of the monitor entered or reentered on invocation of the method, lreturn throws an IllegalMonitorStateException . This can happen, for example, if a synchronized method contains a monitorexit instruction, but no monitorenter instruction, on the object on which the method is synchronized .

Otherwise, if the Java Virtual Machine implementation enforces the rules on structured locking described in §2.11.10 and if the first of those rules is violated during invocation of the current method, then lreturn throws an IllegalMonitorStateException .

Shift left long

lshl = 121 (0x79)

The value1 must be of type long , and value2 must be of type int . The values are popped from the operand stack. A long result is calculated by shifting value1 left by s bit positions, where s is the low 6 bits of value2 . The result is pushed onto the operand stack.

This is equivalent (even if overflow occurs) to multiplication by 2 to the power s . The shift distance actually used is therefore always in the range 0 to 63, inclusive, as if value2 were subjected to a bitwise logical AND with the mask value 0x3f.

Arithmetic shift right long

lshr = 123 (0x7b)

The value1 must be of type long , and value2 must be of type int . The values are popped from the operand stack. A long result is calculated by shifting value1 right by s bit positions, with sign extension, where s is the value of the low 6 bits of value2 . The result is pushed onto the operand stack.

The resulting value is ⌊ value1 / 2 s ⌋, where s is value2 & 0x3f. For non-negative value1 , this is equivalent to truncating long division by 2 to the power s . The shift distance actually used is therefore always in the range 0 to 63, inclusive, as if value2 were subjected to a bitwise logical AND with the mask value 0x3f.

Store long into local variable

lstore index

lstore = 55 (0x37)

The index is an unsigned byte. Both index and index +1 must be indices into the local variable array of the current frame ( §2.6 ). The value on the top of the operand stack must be of type long . It is popped from the operand stack, and the local variables at index and index +1 are set to value .

The lstore opcode can be used in conjunction with the wide instruction ( § wide ) to access a local variable using a two-byte unsigned index.

lstore_<n>

lstore_0 = 63 (0x3f)

lstore_1 = 64 (0x40)

lstore_2 = 65 (0x41)

lstore_3 = 66 (0x42)

Both < n > and < n >+1 must be indices into the local variable array of the current frame ( §2.6 ). The value on the top of the operand stack must be of type long . It is popped from the operand stack, and the local variables at < n > and < n >+1 are set to value .

Each of the lstore_<n> instructions is the same as lstore with an index of < n >, except that the operand < n > is implicit.

Subtract long

lsub = 101 (0x65)

Both value1 and value2 must be of type long . The values are popped from the operand stack. The long result is value1 - value2 . The result is pushed onto the operand stack.

For long subtraction, a-b produces the same result as a+(-b) . For long values, subtraction from zero is the same as negation.

The result is the 64 low-order bits of the true mathematical result in a sufficiently wide two's-complement format, represented as a value of type long . If overflow occurs, then the sign of the result may not be the same as the sign of the mathematical sum of the two values.

Despite the fact that overflow may occur, execution of an lsub instruction never throws a run-time exception.

Logical shift right long

lushr = 125 (0x7d)

The value1 must be of type long , and value2 must be of type int . The values are popped from the operand stack. A long result is calculated by shifting value1 right logically (with zero extension) by the amount indicated by the low 6 bits of value2 . The result is pushed onto the operand stack.

If value1 is positive and s is value2 & 0x3f, the result is the same as that of value1 >> s ; if value1 is negative, the result is equal to the value of the expression ( value1 >> s ) + (2L << ~ s ). The addition of the (2L << ~ s ) term cancels out the propagated sign bit. The shift distance actually used is always in the range 0 to 63, inclusive.

Boolean XOR long

lxor = 131 (0x83)

Both value1 and value2 must be of type long . They are popped from the operand stack. A long result is calculated by taking the bitwise exclusive OR of value1 and value2 . The result is pushed onto the operand stack.

monitorenter

Enter monitor for object

monitorenter = 194 (0xc2)

The objectref must be of type reference .

Each object is associated with a monitor. A monitor is locked if and only if it has an owner. The thread that executes monitorenter attempts to gain ownership of the monitor associated with objectref , as follows:

If the entry count of the monitor associated with objectref is zero, the thread enters the monitor and sets its entry count to one. The thread is then the owner of the monitor.

If the thread already owns the monitor associated with objectref , it reenters the monitor, incrementing its entry count.

If another thread already owns the monitor associated with objectref , the thread blocks until the monitor's entry count is zero, then tries again to gain ownership.

If objectref is null , monitorenter throws a NullPointerException .

A monitorenter instruction may be used with one or more monitorexit instructions ( § monitorexit ) to implement a synchronized statement in the Java programming language ( §3.14 ). The monitorenter and monitorexit instructions are not used in the implementation of synchronized methods, although they can be used to provide equivalent locking semantics. Monitor entry on invocation of a synchronized method, and monitor exit on its return, are handled implicitly by the Java Virtual Machine's method invocation and return instructions, as if monitorenter and monitorexit were used.

The association of a monitor with an object may be managed in various ways that are beyond the scope of this specification. For instance, the monitor may be allocated and deallocated at the same time as the object. Alternatively, it may be dynamically allocated at the time when a thread attempts to gain exclusive access to the object and freed at some later time when no thread remains in the monitor for the object.

The synchronization constructs of the Java programming language require support for operations on monitors besides entry and exit. These include waiting on a monitor ( Object.wait ) and notifying other threads waiting on a monitor ( Object.notifyAll and Object.notify ). These operations are supported in the standard package java.lang supplied with the Java Virtual Machine. No explicit support for these operations appears in the instruction set of the Java Virtual Machine.

monitorexit

Exit monitor for object

monitorexit = 195 (0xc3)

The thread that executes monitorexit must be the owner of the monitor associated with the instance referenced by objectref .

The thread decrements the entry count of the monitor associated with objectref . If as a result the value of the entry count is zero, the thread exits the monitor and is no longer its owner. Other threads that are blocking to enter the monitor are allowed to attempt to do so.

If objectref is null , monitorexit throws a NullPointerException .

Otherwise, if the thread that executes monitorexit is not the owner of the monitor associated with the instance referenced by objectref , monitorexit throws an IllegalMonitorStateException .

Otherwise, if the Java Virtual Machine implementation enforces the rules on structured locking described in §2.11.10 and if the second of those rules is violated by the execution of this monitorexit instruction, then monitorexit throws an IllegalMonitorStateException .

One or more monitorexit instructions may be used with a monitorenter instruction ( § monitorenter ) to implement a synchronized statement in the Java programming language ( §3.14 ). The monitorenter and monitorexit instructions are not used in the implementation of synchronized methods, although they can be used to provide equivalent locking semantics.

The Java Virtual Machine supports exceptions thrown within synchronized methods and synchronized statements differently:

Monitor exit on normal synchronized method completion is handled by the Java Virtual Machine's return instructions. Monitor exit on abrupt synchronized method completion is handled implicitly by the Java Virtual Machine's athrow instruction.

When an exception is thrown from within a synchronized statement, exit from the monitor entered prior to the execution of the synchronized statement is achieved using the Java Virtual Machine's exception handling mechanism ( §3.14 ).

multianewarray

Create new multidimensional array

multianewarray indexbyte1 indexbyte2 dimensions

multianewarray = 197 (0xc5)

..., count1 , [ count2 , ...] →

The dimensions operand is an unsigned byte that must be greater than or equal to 1. It represents the number of dimensions of the array to be created. The operand stack must contain dimensions values. Each such value represents the number of components in a dimension of the array to be created, must be of type int , and must be non-negative. The count1 is the desired length in the first dimension, count2 in the second, etc.

All of the count values are popped off the operand stack. The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class ( §2.6 ), where the value of the index is ( indexbyte1 << 8) | indexbyte2 . The run-time constant pool item at the index must be a symbolic reference to a class, array, or interface type. The named class, array, or interface type is resolved ( §5.4.3.1 ). The resulting entry must be an array class type of dimensionality greater than or equal to dimensions .

A new multidimensional array of the array type is allocated from the garbage-collected heap. If any count value is zero, no subsequent dimensions are allocated. The components of the array in the first dimension are initialized to subarrays of the type of the second dimension, and so on. The components of the last allocated dimension of the array are initialized to the default initial value ( §2.3 , §2.4 ) for the element type of the array type. A reference arrayref to the new array is pushed onto the operand stack.

Otherwise, if the current class does not have permission to access the element type of the resolved array class, multianewarray throws an IllegalAccessError .

Otherwise, if any of the dimensions values on the operand stack are less than zero, the multianewarray instruction throws a NegativeArraySizeException .

It may be more efficient to use newarray or anewarray ( § newarray , § anewarray ) when creating an array of a single dimension.

The array class referenced via the run-time constant pool may have more dimensions than the dimensions operand of the multianewarray instruction. In that case, only the first dimensions of the dimensions of the array are created.

Create new object

new indexbyte1 indexbyte2

new = 187 (0xbb)

The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class ( §2.6 ), where the value of the index is ( indexbyte1 << 8) | indexbyte2 . The run-time constant pool item at the index must be a symbolic reference to a class or interface type. The named class or interface type is resolved ( §5.4.3.1 ) and should result in a class type. Memory for a new instance of that class is allocated from the garbage-collected heap, and the instance variables of the new object are initialized to their default initial values ( §2.3 , §2.4 ). The objectref , a reference to the instance, is pushed onto the operand stack.

On successful resolution of the class, it is initialized ( §5.5 ) if it has not already been initialized.

Otherwise, if the symbolic reference to the class, array, or interface type resolves to an interface or is an abstract class, new throws an InstantiationError .

Otherwise, if execution of this new instruction causes initialization of the referenced class, new may throw an Error as detailed in JLS §15.9.4.

The new instruction does not completely create a new instance; instance creation is not completed until an instance initialization method ( §2.9 ) has been invoked on the uninitialized instance.

Create new array

newarray atype

newarray = 188 (0xbc)

The count must be of type int . It is popped off the operand stack. The count represents the number of elements in the array to be created.

The atype is a code that indicates the type of array to create. It must take one of the following values:

Table 6.1. Array type codes

A new array whose components are of type atype and of length count is allocated from the garbage-collected heap. A reference arrayref to this new array object is pushed into the operand stack. Each of the elements of the new array is initialized to the default initial value ( §2.3 , §2.4 ) for the element type of the array type.

If count is less than zero, newarray throws a NegativeArraySizeException .

In Oracle's Java Virtual Machine implementation, arrays of type boolean ( atype is T_BOOLEAN ) are stored as arrays of 8-bit values and are manipulated using the baload and bastore instructions ( § baload , § bastore ) which also access arrays of type byte . Other implementations may implement packed boolean arrays; the baload and bastore instructions must still be used to access those arrays.

nop = 0 (0x0)

Do nothing.

Pop the top operand stack value

pop = 87 (0x57)

Pop the top value from the operand stack.

The pop instruction must not be used unless value is a value of a category 1 computational type ( §2.11.1 ).

Pop the top one or two operand stack values

pop2 = 88 (0x58)

where each of value1 and value2 is a value of a category 1 computational type ( §2.11.1 ).

Pop the top one or two values from the operand stack.

Set field in object

putfield indexbyte1 indexbyte2

putfield = 181 (0xb5)

..., objectref , value →

The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class ( §2.6 ), where the value of the index is ( indexbyte1 << 8) | indexbyte2 . The run-time constant pool item at that index must be a symbolic reference to a field ( §5.1 ), which gives the name and descriptor of the field as well as a symbolic reference to the class in which the field is to be found. The class of objectref must not be an array. If the field is protected ( §4.6 ), and it is a member of a superclass of the current class, and the field is not declared in the same run-time package ( §5.3 ) as the current class, then the class of objectref must be either the current class or a subclass of the current class.

The referenced field is resolved ( §5.4.3.2 ). The type of a value stored by a putfield instruction must be compatible with the descriptor of the referenced field ( §4.3.2 ). If the field descriptor type is boolean , byte , char , short , or int , then the value must be an int . If the field descriptor type is float , long , or double , then the value must be a float , long , or double , respectively. If the field descriptor type is a reference type, then the value must be of a type that is assignment compatible (JLS §5.2) with the field descriptor type. If the field is final , it must be declared in the current class, and the instruction must occur in an instance initialization method ( <init> ) of the current class ( §2.9 ).

The value and objectref are popped from the operand stack. The objectref must be of type reference . The value undergoes value set conversion ( §2.8.3 ), resulting in value ', and the referenced field in objectref is set to value '.

During resolution of the symbolic reference to the field, any of the exceptions pertaining to field resolution ( §5.4.3.2 ) can be thrown.

Otherwise, if the resolved field is a static field, putfield throws an IncompatibleClassChangeError .

Otherwise, if the field is final , it must be declared in the current class, and the instruction must occur in an instance initialization method ( <init> ) of the current class. Otherwise, an IllegalAccessError is thrown.

Otherwise, if objectref is null , the putfield instruction throws a NullPointerException .

Set static field in class

putstatic indexbyte1 indexbyte2

putstatic = 179 (0xb3)

The type of a value stored by a putstatic instruction must be compatible with the descriptor of the referenced field ( §4.3.2 ). If the field descriptor type is boolean , byte , char , short , or int , then the value must be an int . If the field descriptor type is float , long , or double , then the value must be a float , long , or double , respectively. If the field descriptor type is a reference type, then the value must be of a type that is assignment compatible (JLS §5.2) with the field descriptor type. If the field is final , it must be declared in the current class, and the instruction must occur in the <clinit> method of the current class ( §2.9 ).

The value is popped from the operand stack and undergoes value set conversion ( §2.8.3 ), resulting in value '. The class field is set to value '.

Otherwise, if the resolved field is not a static (class) field or an interface field, putstatic throws an IncompatibleClassChangeError .

Otherwise, if the field is final , it must be declared in the current class, and the instruction must occur in the <clinit> method of the current class. Otherwise, an IllegalAccessError is thrown.

Otherwise, if execution of this putstatic instruction causes initialization of the referenced class or interface, putstatic may throw an Error as detailed in §5.5 .

A putstatic instruction may be used only to set the value of an interface field on the initialization of that field. Interface fields may be assigned to only once, on execution of an interface variable initialization expression when the interface is initialized ( §5.5 , JLS §9.3.1).

Return from subroutine

ret = 169 (0xa9)

The index is an unsigned byte between 0 and 255, inclusive. The local variable at index in the current frame ( §2.6 ) must contain a value of type returnAddress . The contents of the local variable are written into the Java Virtual Machine's pc register, and execution continues there.

Note that jsr ( § jsr ) pushes the address onto the operand stack and ret gets it out of a local variable. This asymmetry is intentional.

In Oracle's implementation of a compiler for the Java programming language prior to Java SE 6, the ret instruction was used with the jsr and jsr_w instructions ( § jsr , § jsr_w ) in the implementation of the finally clause ( §3.13 , §4.10.2.5 ).

The ret instruction should not be confused with the return instruction ( § return ). A return instruction returns control from a method to its invoker, without passing any value back to the invoker.

The ret opcode can be used in conjunction with the wide instruction ( § wide ) to access a local variable using a two-byte unsigned index.

Return void from method

return = 177 (0xb1)

The current method must have return type void . If the current method is a synchronized method, the monitor entered or reentered on invocation of the method is updated and possibly exited as if by execution of a monitorexit instruction ( § monitorexit ) in the current thread. If no exception is thrown, any values on the operand stack of the current frame ( §2.6 ) are discarded.

If the Java Virtual Machine implementation does not enforce the rules on structured locking described in §2.11.10 , then if the current method is a synchronized method and the current thread is not the owner of the monitor entered or reentered on invocation of the method, return throws an IllegalMonitorStateException . This can happen, for example, if a synchronized method contains a monitorexit instruction, but no monitorenter instruction, on the object on which the method is synchronized .

Otherwise, if the Java Virtual Machine implementation enforces the rules on structured locking described in §2.11.10 and if the first of those rules is violated during invocation of the current method, then return throws an IllegalMonitorStateException .

Load short from array

saload = 53 (0x35)

The arrayref must be of type reference and must refer to an array whose components are of type short . The index must be of type int . Both arrayref and index are popped from the operand stack. The component of the array at index is retrieved and sign-extended to an int value . That value is pushed onto the operand stack.

If arrayref is null , saload throws a NullPointerException .

Otherwise, if index is not within the bounds of the array referenced by arrayref , the saload instruction throws an ArrayIndexOutOfBoundsException .

Store into short array

sastore = 86 (0x56)

The arrayref must be of type reference and must refer to an array whose components are of type short . Both index and value must be of type int . The arrayref , index , and value are popped from the operand stack. The int value is truncated to a short and stored as the component of the array indexed by index .

If arrayref is null , sastore throws a NullPointerException .

Otherwise, if index is not within the bounds of the array referenced by arrayref , the sastore instruction throws an ArrayIndexOutOfBoundsException .

sipush byte1 byte2

sipush = 17 (0x11)

The immediate unsigned byte1 and byte2 values are assembled into an intermediate short where the value of the short is ( byte1 << 8) | byte2 . The intermediate value is then sign-extended to an int value . That value is pushed onto the operand stack.

Swap the top two operand stack values

swap = 95 (0x5f)

..., value1 , value2

Swap the top two values on the operand stack.

The swap instruction must not be used unless value1 and value2 are both values of a category 1 computational type ( §2.11.1 ).

The Java Virtual Machine does not provide an instruction implementing a swap on operands of category 2 computational types.

tableswitch

Access jump table by index and jump

tableswitch <0-3 byte pad> defaultbyte1 defaultbyte2 defaultbyte3 defaultbyte4 lowbyte1 lowbyte2 lowbyte3 lowbyte4 highbyte1 highbyte2 highbyte3 highbyte4 jump offsets...

tableswitch = 170 (0xaa)

..., index →

A tableswitch is a variable-length instruction. Immediately after the tableswitch opcode, between zero and three bytes must act as padding, such that defaultbyte1 begins at an address that is a multiple of four bytes from the start of the current method (the opcode of its first instruction). Immediately after the padding are bytes constituting three signed 32-bit values: default , low , and high . Immediately following are bytes constituting a series of high - low + 1 signed 32-bit offsets. The value low must be less than or equal to high . The high - low + 1 signed 32-bit offsets are treated as a 0-based jump table. Each of these signed 32-bit values is constructed as ( byte1 << 24) | ( byte2 << 16) | ( byte3 << 8) | byte4 .

The index must be of type int and is popped from the operand stack. If index is less than low or index is greater than high , then a target address is calculated by adding default to the address of the opcode of this tableswitch instruction. Otherwise, the offset at position index - low of the jump table is extracted. The target address is calculated by adding that offset to the address of the opcode of this tableswitch instruction. Execution then continues at the target address.

The target address that can be calculated from each jump table offset, as well as the one that can be calculated from default , must be the address of an opcode of an instruction within the method that contains this tableswitch instruction.

The alignment required of the 4-byte operands of the tableswitch instruction guarantees 4-byte alignment of those operands if and only if the method that contains the tableswitch starts on a 4-byte boundary.

Extend local variable index by additional bytes

wide <opcode> indexbyte1 indexbyte2

where <opcode> is one of iload , fload , aload , lload , dload , istore , fstore , astore , lstore , dstore , or ret

wide iinc indexbyte1 indexbyte2 constbyte1 constbyte2

wide = 196 (0xc4)

Same as modified instruction

The wide instruction modifies the behavior of another instruction. It takes one of two formats, depending on the instruction being modified. The first form of the wide instruction modifies one of the instructions iload , fload , aload , lload , dload , istore , fstore , astore , lstore , dstore , or ret ( § iload , § fload , § aload , § lload , § dload , § istore , § fstore , § astore , § lstore , § dstore , § ret ). The second form applies only to the iinc instruction ( § iinc ).

In either case, the wide opcode itself is followed in the compiled code by the opcode of the instruction wide modifies. In either form, two unsigned bytes indexbyte1 and indexbyte2 follow the modified opcode and are assembled into a 16-bit unsigned index to a local variable in the current frame ( §2.6 ), where the value of the index is ( indexbyte1 << 8) | indexbyte2 . The calculated index must be an index into the local variable array of the current frame. Where the wide instruction modifies an lload , dload , lstore , or dstore instruction, the index following the calculated index (index + 1) must also be an index into the local variable array. In the second form, two immediate unsigned bytes constbyte1 and constbyte2 follow indexbyte1 and indexbyte2 in the code stream. Those bytes are also assembled into a signed 16-bit constant, where the constant is ( constbyte1 << 8) | constbyte2 .

The widened bytecode operates as normal, except for the use of the wider index and, in the case of the second form, the larger increment range.

Although we say that wide "modifies the behavior of another instruction," the wide instruction effectively treats the bytes constituting the modified instruction as operands, denaturing the embedded instruction in the process. In the case of a modified iinc instruction, one of the logical operands of the iinc is not even at the normal offset from the opcode. The embedded instruction must never be executed directly; its opcode must never be the target of any control transfer instruction.

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Operators are symbols that perform operations on variables and values. For example, + is an operator used for addition, while * is also an operator used for multiplication.

Operators in Java can be classified into 5 types:

• Arithmetic Operators
• Assignment Operators
• Relational Operators
• Logical Operators
• Unary Operators
• Bitwise Operators

1. Java Arithmetic Operators

Arithmetic operators are used to perform arithmetic operations on variables and data. For example,

Here, the + operator is used to add two variables a and b . Similarly, there are various other arithmetic operators in Java.

Example 1: Arithmetic Operators

In the above example, we have used + , - , and * operators to compute addition, subtraction, and multiplication operations.

/ Division Operator

Note the operation, a / b in our program. The / operator is the division operator.

If we use the division operator with two integers, then the resulting quotient will also be an integer. And, if one of the operands is a floating-point number, we will get the result will also be in floating-point.

% Modulo Operator

The modulo operator % computes the remainder. When a = 7 is divided by b = 4 , the remainder is 3 .

Note : The % operator is mainly used with integers.

2. Java Assignment Operators

Assignment operators are used in Java to assign values to variables. For example,

Here, = is the assignment operator. It assigns the value on its right to the variable on its left. That is, 5 is assigned to the variable age .

Let's see some more assignment operators available in Java.

Example 2: Assignment Operators

3. java relational operators.

Relational operators are used to check the relationship between two operands. For example,

Here, < operator is the relational operator. It checks if a is less than b or not.

It returns either true or false .

Example 3: Relational Operators

Note : Relational operators are used in decision making and loops.

4. Java Logical Operators

Logical operators are used to check whether an expression is true or false . They are used in decision making.

Example 4: Logical Operators

Working of Program

• (5 > 3) && (8 > 5) returns true because both (5 > 3) and (8 > 5) are true .
• (5 > 3) && (8 < 5) returns false because the expression (8 < 5) is false .
• (5 < 3) || (8 > 5) returns true because the expression (8 > 5) is true .
• (5 > 3) || (8 < 5) returns true because the expression (5 > 3) is true .
• (5 < 3) || (8 < 5) returns false because both (5 < 3) and (8 < 5) are false .
• !(5 == 3) returns true because 5 == 3 is false .
• !(5 > 3) returns false because 5 > 3 is true .

5. Java Unary Operators

Unary operators are used with only one operand. For example, ++ is a unary operator that increases the value of a variable by 1 . That is, ++5 will return 6 .

Different types of unary operators are:

• Increment and Decrement Operators

Java also provides increment and decrement operators: ++ and -- respectively. ++ increases the value of the operand by 1 , while -- decrease it by 1 . For example,

Here, the value of num gets increased to 6 from its initial value of 5 .

Example 5: Increment and Decrement Operators

In the above program, we have used the ++ and -- operator as prefixes (++a, --b) . We can also use these operators as postfix (a++, b++) .

There is a slight difference when these operators are used as prefix versus when they are used as a postfix.

To learn more about these operators, visit increment and decrement operators .

6. Java Bitwise Operators

Bitwise operators in Java are used to perform operations on individual bits. For example,

Here, ~ is a bitwise operator. It inverts the value of each bit ( 0 to 1 and 1 to 0 ).

The various bitwise operators present in Java are:

These operators are not generally used in Java. To learn more, visit Java Bitwise and Bit Shift Operators .

Other operators

Besides these operators, there are other additional operators in Java.

The instanceof operator checks whether an object is an instanceof a particular class. For example,

Here, str is an instance of the String class. Hence, the instanceof operator returns true . To learn more, visit Java instanceof .

The ternary operator (conditional operator) is shorthand for the if-then-else statement. For example,

Here's how it works.

• If the Expression is true , expression1 is assigned to the variable .
• If the Expression is false , expression2 is assigned to the variable .

Let's see an example of a ternary operator.

In the above example, we have used the ternary operator to check if the year is a leap year or not. To learn more, visit the Java ternary operator .

Now that you know about Java operators, it's time to know about the order in which operators are evaluated. To learn more, visit Java Operator Precedence .

Table of Contents

• Introduction
• Java Arithmetic Operators
• Java Assignment Operators
• Java Relational Operators
• Java Logical Operators
• Java Unary Operators
• Java Bitwise Operators

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Static Single Assignment was presented in 1988 by Barry K. Rosen, Mark N, Wegman, and F. Kenneth Zadeck. 

In compiler design, Static Single Assignment ( shortened SSA) is a means of structuring the IR (intermediate representation) such that every variable is allotted a value only once and every variable is defined before it’s use. The prime use of SSA is it simplifies and improves the results of compiler optimisation algorithms, simultaneously by simplifying the variable properties. Some Algorithms improved by application of SSA – 

• Constant Propagation –   Translation of calculations from runtime to compile time. E.g. – the instruction v = 2*7+13 is treated like v = 27
• Value Range Propagation –   Finding the possible range of values a calculation could result in.
• Dead Code Elimination – Removing the code which is not accessible and will have no effect on results whatsoever.
• Strength Reduction – Replacing computationally expensive calculations by inexpensive ones.
• Register Allocation – Optimising the use of registers for calculations.

Any code can be converted to SSA form by simply replacing the target variable of each code segment with a new variable and substituting each use of a variable with the new edition of the variable reaching that point. Versions are created by splitting the original variables existing in IR and are represented by original name with a subscript such that every variable gets its own version.

Example #1:

Convert the following code segment to SSA form:

Here x,y,z,s,p,q are original variables and x 2 , s 2 , s 3 , s 4 are versions of x and s. 

Example #2:

Here a,b,c,d,e,q,s are original variables and a 2 , q 2 , q 3 are versions of a and q. 

Phi function and SSA codes

The three address codes may also contain goto statements, and thus a variable may assume value from two different paths.

Consider the following example:-

Example #3:

When we try to convert the above three address code to SSA form, the output looks like:-

Attempt #3:

We need to be able to decide what value shall y take, out of x 1 and x 2 . We thus introduce the notion of phi functions, which resolves the correct value of the variable from two different computation paths due to branching.

Hence, the correct SSA codes for the example will be:-

Solution #3:

Thus, whenever a three address code has a branch and control may flow along two different paths, we need to use phi functions for appropriate addresses.

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Creating Tasks and Accepting Reservations: Accept a Reservation using Assignment Callback Instructions

Remember when we created a Task and accepted it using the Reservations subresource of the REST API? I do. And it was grand.

This time, we'll create another Task, again using the REST API, but we will have our server accept the Reservation as soon as it is notified, via a synchronous HTTP response.

Before we create the next Task, once again make sure that our Worker Alice is in a non-available Activity state.

This time, before bringing Alice online, we need to make changes to our assignment_callback method in our TwilioTaskRouterServlet . Open it and modify the existing code to reflect the following:

TwilioTaskRouterServlet.java

Instead of returning an empty JSON document as before, we've included an 'assignment instruction' in our response. The 'accept' assignment instruction tells TaskRouter to automatically accept the Reservation and assign the Task to the Worker it has been reserved for.

Now, click 'Tasks' in the main navigation, and you should see that the Task has an Assignment Status of 'assigned':

What actually happened is that Alice was reserved for a very short period of time. TaskRouter made a request to your web server at the Assignment Callback URL, and your server told TaskRouter to accept the Reservation. At that point, Alice's Activity transitioned to the 'Assignment Activity' of the TaskQueue that assigned the Task, as it did in the previous step.

And that's that. We created another Task using the REST API, accepted it via an assignment instruction at our Workflow's Assignment Callback URL and saw that this immediately accepted the Reservation for our Worker.

Onward! Next we learn about shortcuts to create Tasks originating from Twilio phone calls.

Part 3: Create Tasks from Phone Calls using TwiML »

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