Chapter 4. The class File Format

4.1. The ClassFile Structure

ClassFile {
    u4             magic;
    u2             minor_version;
    u2             major_version;
    u2             constant_pool_count;
    cp_info        constant_pool[constant_pool_count-1];
    u2             access_flags;
    u2             this_class;
    u2             super_class;
    u2             interfaces_count;
    u2             interfaces[interfaces_count];
    u2             fields_count;
    field_info     fields[fields_count];
    u2             methods_count;
    method_info    methods[methods_count];
    u2             attributes_count;
    attribute_info attributes[attributes_count];
}

4.3. Descriptors

4.3.2. Field Descriptors

FieldType term	Type	Interpretation
`B`	`byte`	signed byte
`C`	`char`	Unicode character code point in the Basic Multilingual Plane, encoded with UTF-16
`D`	`double`	double-precision floating-point value
`F`	`float`	single-precision floating-point value
`I`	`int`	integer
`J`	`long`	long integer
`L` ClassName ;	`reference`	an instance of class ClassName
`S`	`short`	signed short
`Z`	`boolean`	`true` or `false`
`[`	`reference`	one array dimension

4.4. The Constant Pool

cp_info {
    u1 tag;
    u1 info[];
}

Constant Type	Value
`CONSTANT_Class`	7
`CONSTANT_Fieldref`	9
`CONSTANT_Methodref`	10
`CONSTANT_InterfaceMethodref`	11
`CONSTANT_String`	8
`CONSTANT_Integer`	3
`CONSTANT_Float`	4
`CONSTANT_Long`	5
`CONSTANT_Double`	6
`CONSTANT_NameAndType`	12
`CONSTANT_Utf8`	1
`CONSTANT_MethodHandle`	15
`CONSTANT_MethodType`	16
`CONSTANT_InvokeDynamic`	18

4.5. Fields

field_info {
    u2             access_flags;
    u2             name_index;
    u2             descriptor_index;
    u2             attributes_count;
    attribute_info attributes[attributes_count];
}

Flag Name	Value	Interpretation
`ACC_PUBLIC`	0x0001	Declared `public`; may be accessed from outside its package.
`ACC_PRIVATE`	0x0002	Declared `private`; usable only within the defining class.
`ACC_PROTECTED`	0x0004	Declared `protected`; may be accessed within subclasses.
`ACC_STATIC`	0x0008	Declared `static`.
`ACC_FINAL`	0x0010	Declared `final`; never directly assigned to after object construction (JLS §17.5).
`ACC_VOLATILE`	0x0040	Declared `volatile`; cannot be cached.
`ACC_TRANSIENT`	0x0080	Declared `transient`; not written or read by a persistent object manager.
`ACC_SYNTHETIC`	0x1000	Declared synthetic; not present in the source code.
`ACC_ENUM`	0x4000	Declared as an element of an `enum`.

4.6. Methods

method_info {
    u2             access_flags;
    u2             name_index;
    u2             descriptor_index;
    u2             attributes_count;
    attribute_info attributes[attributes_count];
}

Flag Name	Value	Interpretation
`ACC_PUBLIC`	0x0001	Declared `public`; may be accessed from outside its package.
`ACC_PRIVATE`	0x0002	Declared `private`; accessible only within the defining class.
`ACC_PROTECTED`	0x0004	Declared `protected`; may be accessed within subclasses.
`ACC_STATIC`	0x0008	Declared `static`.
`ACC_FINAL`	0x0010	Declared `final`; must not be overridden (§5.4.5).
`ACC_SYNCHRONIZED`	0x0020	Declared `synchronized`; invocation is wrapped by a monitor use.
`ACC_BRIDGE`	0x0040	A bridge method, generated by the compiler.
`ACC_VARARGS`	0x0080	Declared with variable number of arguments.
`ACC_NATIVE`	0x0100	Declared `native`; implemented in a language other than Java.
`ACC_ABSTRACT`	0x0400	Declared `abstract`; no implementation is provided.
`ACC_STRICT`	0x0800	Declared `strictfp`; floating-point mode is FP-strict.
`ACC_SYNTHETIC`	0x1000	Declared synthetic; not present in the source code.

4.7. Attributes

attribute_info {
    u2 attribute_name_index;
    u4 attribute_length;
    u1 info[attribute_length];
}

References

Chapter 4. The class File Format