JEP 484: Class-File API

https://openjdk.org/jeps/484

The new Class-File API (JEP 484) is now a fully supported feature of Java 24. It provides a clean, safe, and standard way to inspect and manipulate .class files — no more relying on external tools like ASM.

EP 484 introduces a standard API for parsing, generating, and transforming Java class files. This API resides in the java.lang.classfile package and provides a structured way to interact with class file elements without relying on third-party libraries.

Key Components of the Class-File API

The API is built around three main abstractions:

1. Elements: Immutable descriptions of parts of a class file, such as instructions, attributes, fields, methods, or the entire class file.​openjdk.org

2. Builders: Corresponding builders for compound elements that facilitate the creation or transformation of class file components.​openjdk.org

3. Transforms: Functions that take an element and a builder to mediate how, if at all, that element is transformed into other elements.​

example of sealed interface:

public sealed interface ClassModel
        extends CompoundElement<ClassElement>, AttributedElement
        permits ClassImpl {

run :

ClassFileParser

result: 
Class Name: com/wlodar/jeeps/jep484classfileapi/SampleForClassApi
Super Class: java/lang/Object
Access Flags: AccessFlags[flags=33]

Methods:
- <init>()V
- hello(Ljava/lang/String;)V

🔍 What does Access Flags: 33 mean?

The access flags are stored as a bitmask integer in the .class file.

Java uses constants like:

Flag	Hex	Decimal
ACC_PUBLIC	0x0001	1
ACC_SUPER	0x0020	32

33 = 1 (public) + 32 (super)

So:

cssCopyEditAccessFlags[flags=33] → [PUBLIC, SUPER]

✅ It means:

• The class is public

• The ACC_SUPER bit is set — which is always set in modern .class files and signals to the JVM to use special superclass method invocation rules