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The Java® Virtual Machine Specification
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The Java® Virtual Machine Specification

Java SE 21 Edition

Tim Lindholm

Frank Yellin

Gilad Bracha

Alex Buckley

Daniel Smith

2023-08-23

Table of Contents

1. Introduction

1.1. A Bit of History
1.2. The Java Virtual Machine
1.3. Organization of the Specification
1.4. Notation
1.5. Feedback

2. The Structure of the Java Virtual Machine

2.1. The class File Format

2.2. Data Types

2.3. Primitive Types and Values

2.3.1. Integral Types and Values
2.3.2. Floating-Point Types and Values
2.3.3. The returnAddress Type and Values
2.3.4. The boolean Type

2.4. Reference Types and Values

2.5. Run-Time Data Areas

2.5.1. The pc Register
2.5.2. Java Virtual Machine Stacks
2.5.3. Heap
2.5.4. Method Area
2.5.5. Run-Time Constant Pool
2.5.6. Native Method Stacks

2.6. Frames

2.6.1. Local Variables
2.6.2. Operand Stacks
2.6.3. Dynamic Linking
2.6.4. Normal Method Invocation Completion
2.6.5. Abrupt Method Invocation Completion

2.7. Representation of Objects

2.8. Floating-Point Arithmetic

2.9. Special Methods

2.9.1. Instance Initialization Methods
2.9.2. Class Initialization Methods
2.9.3. Signature Polymorphic Methods

2.10. Exceptions

2.11. Instruction Set Summary

2.11.1. Types and the Java Virtual Machine
2.11.2. Load and Store Instructions
2.11.3. Arithmetic Instructions
2.11.4. Type Conversion Instructions
2.11.5. Object Creation and Manipulation
2.11.6. Operand Stack Management Instructions
2.11.7. Control Transfer Instructions
2.11.8. Method Invocation and Return Instructions
2.11.9. Throwing Exceptions
2.11.10. Synchronization

2.12. Class Libraries

2.13. Public Design, Private Implementation

3. Compiling for the Java Virtual Machine

3.1. Format of Examples
3.2. Use of Constants, Local Variables, and Control Constructs
3.3. Arithmetic
3.4. Accessing the Run-Time Constant Pool
3.5. More Control Examples
3.6. Receiving Arguments
3.7. Invoking Methods
3.8. Working with Class Instances
3.9. Arrays
3.10. Compiling Switches
3.11. Operations on the Operand Stack
3.12. Throwing and Handling Exceptions
3.13. Compiling finally
3.14. Synchronization
3.15. Annotations
3.16. Modules

4. The class File Format

4.1. The ClassFile Structure

4.2.1. Binary Class and Interface Names
4.2.2. Unqualified Names
4.2.3. Module and Package Names

4.3. Descriptors

4.3.1. Grammar Notation
4.3.2. Field Descriptors
4.3.3. Method Descriptors

4.4. The Constant Pool

4.4.1. The CONSTANT_Class_info Structure
4.4.2. The CONSTANT_Fieldref_info, CONSTANT_Methodref_info, and CONSTANT_InterfaceMethodref_info Structures
4.4.3. The CONSTANT_String_info Structure
4.4.4. The CONSTANT_Integer_info and CONSTANT_Float_info Structures
4.4.5. The CONSTANT_Long_info and CONSTANT_Double_info Structures
4.4.6. The CONSTANT_NameAndType_info Structure
4.4.7. The CONSTANT_Utf8_info Structure
4.4.8. The CONSTANT_MethodHandle_info Structure
4.4.9. The CONSTANT_MethodType_info Structure
4.4.10. The CONSTANT_Dynamic_info and CONSTANT_InvokeDynamic_info Structures
4.4.11. The CONSTANT_Module_info Structure
4.4.12. The CONSTANT_Package_info Structure

4.5. Fields

4.6. Methods

4.7. Attributes

4.7.1. Defining and Naming New Attributes

4.7.2. The ConstantValue Attribute

4.7.3. The Code Attribute

4.7.4. The StackMapTable Attribute

4.7.5. The Exceptions Attribute

4.7.6. The InnerClasses Attribute

4.7.7. The EnclosingMethod Attribute

4.7.8. The Synthetic Attribute

4.7.9. The Signature Attribute

4.7.9.1. Signatures

4.7.10. The SourceFile Attribute

4.7.11. The SourceDebugExtension Attribute

4.7.12. The LineNumberTable Attribute

4.7.13. The LocalVariableTable Attribute

4.7.14. The LocalVariableTypeTable Attribute

4.7.15. The Deprecated Attribute

4.7.16. The RuntimeVisibleAnnotations Attribute

4.7.16.1. The element_value structure

4.7.17. The RuntimeInvisibleAnnotations Attribute

4.7.18. The RuntimeVisibleParameterAnnotations Attribute

4.7.19. The RuntimeInvisibleParameterAnnotations Attribute

4.7.20. The RuntimeVisibleTypeAnnotations Attribute

4.7.20.1. The target_info union
4.7.20.2. The type_path structure

4.7.21. The RuntimeInvisibleTypeAnnotations Attribute

4.7.22. The AnnotationDefault Attribute

4.7.23. The BootstrapMethods Attribute

4.7.24. The MethodParameters Attribute

4.7.25. The Module Attribute

4.7.26. The ModulePackages Attribute

4.7.27. The ModuleMainClass Attribute

4.7.28. The NestHost Attribute

4.7.29. The NestMembers Attribute

4.7.30. The Record Attribute

4.7.31. The PermittedSubclasses Attribute

4.8. Format Checking

4.9. Constraints on Java Virtual Machine Code

4.9.1. Static Constraints
4.9.2. Structural Constraints

4.10. Verification of class Files

4.10.1. Verification by Type Checking

4.10.1.1. Accessors for Java Virtual Machine Artifacts

4.10.1.2. Verification Type System

4.10.1.3. Instruction Representation

4.10.1.4. Stack Map Frames and Type Transitions

4.10.1.5. Type Checking Abstract and Native Methods

4.10.1.6. Type Checking Methods with Code

4.10.1.7. Type Checking Load and Store Instructions

4.10.1.8. Type Checking for protected Members

4.10.1.9. Type Checking Instructions

4.10.2. Verification by Type Inference

4.10.2.1. The Process of Verification by Type Inference
4.10.2.2. The Bytecode Verifier
4.10.2.3. Values of Types long and double
4.10.2.4. Instance Initialization Methods and Newly Created Objects
4.10.2.5. Exceptions and finally

4.11. Limitations of the Java Virtual Machine

5. Loading, Linking, and Initializing

5.1. The Run-Time Constant Pool

5.2. Java Virtual Machine Startup

5.3. Creation and Loading

5.3.1. Loading Using the Bootstrap Class Loader
5.3.2. Loading Using a User-defined Class Loader
5.3.3. Creating Array Classes
5.3.4. Loading Constraints
5.3.5. Deriving a Class from a class File Representation
5.3.6. Modules and Layers

5.4. Linking

5.4.1. Verification

5.4.2. Preparation

5.4.3. Resolution

5.4.3.1. Class and Interface Resolution
5.4.3.2. Field Resolution
5.4.3.3. Method Resolution
5.4.3.4. Interface Method Resolution
5.4.3.5. Method Type and Method Handle Resolution
5.4.3.6. Dynamically-Computed Constant and Call Site Resolution

5.4.4. Access Control

5.4.5. Method Overriding

5.4.6. Method Selection

5.5. Initialization

5.6. Binding Native Method Implementations

5.7. Java Virtual Machine Termination

6. The Java Virtual Machine Instruction Set

6.1. Assumptions: The Meaning of "Must"

6.2. Reserved Opcodes

6.3. Virtual Machine Errors

6.4. Format of Instruction Descriptions

6.5. Instructions

aconst_null

aload_<n>

anewarray

arraylength

astore_<n>

checkcast

dconst_<d>

dload_<n>

dstore_<n>

fconst_<f>

fload_<n>

fstore_<n>

getstatic

iconst_<i>

if_acmp<cond>

if_icmp<cond>

ifnonnull

iload_<n>

instanceof

invokedynamic

invokeinterface

invokespecial

invokestatic

invokevirtual

istore_<n>

lconst_<l>

lload_<n>

lookupswitch

lstore_<n>

monitorenter

monitorexit

multianewarray

putstatic

tableswitch

7. Opcode Mnemonics by Opcode

A. Limited License Grant

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