Fields in a Class File

magic

This field holds the magic number 0xcafebabe that identifies a Java class file.

minor_version, major_version

These fields hold the minor and major version numbers of the compiler that produced this class file. A JVM supports class files having a given major version number and minor version numbers 0 through some particular minor_version.

constant_pool[]

This is a table of constant_pool_count - 1 structures representing various constant values, names, descriptors and other things that are referred to within the class file. There is no entry 0; this entry is reserved for internal use by a JVM. Each of the entries have a tag to indicate its type.

The following table contains a list of the types and their description:

Structures of type CONSTANT_Long and CONSTANT_Double take up two entries in the constant_pool for historic reasons.

access_flags

This is a mask of modifiers used with class and interface declarations. The following flags are defined:

this_class
This is an index into the constant_pool[]. The entry at that index must be a CONSTANT_Class_info representing the class or interface defined by this file.

super_class
For a class the value of this field is either zero, in which case this class file represents the class java.lang.Object, or an index into the constant_pool[]. The entry at that index must be a CONSTANT_Class_info representing the superclass of the class defined by this class file.

For an interface the value of this field must always be an index into the constant_pool[]. The entry at that index must be a CONSTANT_Class_info representing the class java.lang.Object.

interfaces[]
Each value in this table with interfaces_count entries must be an index into the constant_pool[], the entry at that index must be a CONSTANT_Class_info representing an interface which is a direct superinterface of this class or interface.

fields[]
Each entry in this table with fields_count entries is a complete description of a field.

methods[]
Each entry in this table with methods_count entries gives a complete description of and JVM code for a method in the class or interface.

attributes[]
Each entry in this table with attributes_count entries must be a variable-length attribute structure. For the class file the only attribute defined is the SourceFile attribute containing the name of the source file.