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Java Classes

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hydrophobis edited this page Mar 25, 2025 · 1 revision

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Access Flags

ACC_PUBLIC:

Marks the class or member as public, making it accessible from any other class.

ACC_PRIVATE:

Marks the class or member as private, restricting access to the defining class only.

ACC_PROTECTED:

Marks the class or member as protected, making it accessible within its own package and by subclasses.

ACC_STATIC:

Marks the class or member as static, meaning it belongs to the class itself rather than an instance.

ACC_FINAL:

Marks the class or member as final, meaning it cannot be subclassed or overridden.

ACC_SUPER:

Indicates the class has a superclass. Used in conjunction with ACC_PUBLIC for classes that inherit from a parent class. Example:

ACC_PUBLIC | ACC_SUPER // Public class with a superclass
emit_u2("this class name")
emit_u2("super class name")

ACC_SYNCHRONIZED:

Used for methods to indicate that the method should be executed with synchronization, ensuring only one thread can access it at a time.

ACC_NATIVE:

Marks a method as native, meaning its implementation is in a language other than Java (typically C or C++) and will be linked at runtime.

ACC_INTERFACE:

Marks the class as an interface, meaning it cannot have instance methods but can contain abstract methods to be implemented by classes.

ACC_ABSTRACT:

Marks the class or method as abstract, indicating it cannot be instantiated (for classes) or must be implemented by subclasses (for methods).

ACC_STRICT:

Forces the JVM to follow the IEEE 754 floating-point standard strictly, ensuring precise floating-point calculations.

Class Header

  • Magic number: 0xCAFEBABE to identify the file as a valid Java class file.
  • Version: Java 8 version with minor and major version specified.

Class Footer

  • Access flags: Marks the class's access level, ensuring proper permissions.
  • Class references: The current class and its superclass references.

Code Attribute

  • Code Attribute Start: Defines the start of a code attribute, including the name, stack, and locals.
  • Code Attribute End: Completes the code block and adds exception handling or other attributes.

For detailed explanations on each component and their roles in Java class file structure, explore the individual sections.

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