Methods of classfile

Methods

Each method, including each instance initialization method (​ ​§2.9​​​) and the class or interface initialization method (​ ​§2.9​​​), is described by a ​​method_info​​ structure.

No two methods in one ​​class​​​ file may have the same name and descriptor (​ ​§4.3.3​​).

The structure has the following format:

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

        
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The items of the ​​method_info​​ structure are as follows:

access_flags

The value of the ​​access_flags​​​ item is a mask of flags used to denote access permission to and properties of this method. The interpretation of each flag, when set, is specified in ​ ​Table 4.6-A​​.

Table 4.6-A. Method access and property flags

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.

Methods of classes may have any of the flags in ​ ​Table 4.6-A​​​ set. However, each method of a class may have at most one of its ​​ACC_PUBLIC​​​, ​​ACC_PRIVATE​​​, and ​​ACC_PROTECTED​​ flags set (JLS §8.4.3).

Methods of interfaces may have any of the flags in ​ ​Table 4.6-A​​​ set except ​​ACC_PROTECTED​​​, ​​ACC_FINAL​​​, ​​ACC_SYNCHRONIZED​​​, and ​​ACC_NATIVE​​​ (JLS §9.4). In a ​​class​​​ file whose version number is less than 52.0, each method of an interface must have its ​​ACC_PUBLIC​​​ and ​​ACC_ABSTRACT​​​flags set; in a ​​class​​​ file whose version number is 52.0 or above, each method of an interface must have exactly one of its ​​ACC_PUBLIC​​​ and ​​ACC_PRIVATE​​ flags set.

If a method of a class or interface has its ​​ACC_ABSTRACT​​​ flag set, it must not have any of its ​​ACC_PRIVATE​​​, ​​ACC_STATIC​​​, ​​ACC_FINAL​​​, ​​ACC_SYNCHRONIZED​​​, ​​ACC_NATIVE​​​, or ​​ACC_STRICT​​ flags set.

Each instance initialization method (​ ​§2.9​​​) may have at most one of its ​​ACC_PUBLIC​​​, ​​ACC_PRIVATE​​​, and ​​ACC_PROTECTED​​​ flags set, and may also have its ​​ACC_VARARGS​​​, ​​ACC_STRICT​​​, and ​​ACC_SYNTHETIC​​​ flags set, but must not have any of the other flags in ​ ​Table 4.6-A​​ set.

Class and interface initialization methods are called implicitly by the Java Virtual Machine. The value of their ​​access_flags​​​ item is ignored except for the setting of the ​​ACC_STRICT​​ flag.

The ​​ACC_BRIDGE​​ flag is used to indicate a bridge method generated by a compiler for the Java programming language.

The ​​ACC_VARARGS​​​ flag indicates that this method takes a variable number of arguments at the source code level. A method declared to take a variable number of arguments must be compiled with the ​​ACC_VARARGS​​​ flag set to 1. All other methods must be compiled with the ​​ACC_VARARGS​​ flag set to 0.

The ​​ACC_SYNTHETIC​​​ flag indicates that this method was generated by a compiler and does not appear in source code, unless it is one of the methods named in ​ ​§4.7.8​​.

All bits of the ​​access_flags​​​ item not assigned in ​ ​Table 4.6-A​​​ are reserved for future use. They should be set to zero in generated ​​class​​ files and should be ignored by Java Virtual Machine implementations.

name_index

The value of the ​​name_index​​​ item must be a valid index into the ​​constant_pool​​​ table. The ​​constant_pool​​​ entry at that index must be a ​​CONSTANT_Utf8_info​​​ structure (​ ​§4.4.7​​​) representing either one of the special method names ​​<init>​​​ or ​​<clinit>​​​ (​ ​§2.9​​​), or a valid unqualified name denoting a method (​ ​§4.2.2​​).

descriptor_index

The value of the ​​descriptor_index​​​ item must be a valid index into the ​​constant_pool​​​ table. The ​​constant_pool​​​ entry at that index must be a ​​CONSTANT_Utf8_info​​​ structure representing a valid method descriptor (​ ​§4.3.3​​).

A future edition of this specification may require that the last parameter descriptor of the method descriptor is an array type if the ​​ACC_VARARGS​​​ flag is set in the ​​access_flags​​ item.

attributes_count

The value of the ​​attributes_count​​ item indicates the number of additional attributes of this method.

attributes[]

Each value of the ​​attributes​​​ table must be an ​​attribute_info​​​ structure (​ ​§4.7​​).

A method can have any number of optional attributes associated with it.

The attributes defined by this specification as appearing in the ​​attributes​​​ table of a ​​method_info​​​ structure are listed in ​ ​Table 4.7-C​​.

The rules concerning attributes defined to appear in the ​​attributes​​​ table of a ​​method_info​​​ structure are given in ​ ​§4.7​​.

The rules concerning non-predefined attributes in the ​​attributes​​​ table of a ​​method_info​​​ structure are given in ​ ​§4.7.1​​.