4.5_Fields.md

4.5. Fields

Each field is described by a field_info structure.

No two fields in one class file may have the same name and descriptor (§4.3.2).

The structure has the following format:

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

The items of the field_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 field. The interpretation of each flag, when set, is specified in Table 4.5-A.Table 4.5-A. Field access and property flagsFlag NameValueInterpretationACC_PUBLIC0x0001Declared public; may be accessed from outside its package.ACC_PRIVATE0x0002Declared private; usable only within the defining class.ACC_PROTECTED0x0004Declared protected; may be accessed within subclasses.ACC_STATIC0x0008Declared static.ACC_FINAL0x0010Declared final; never directly assigned to after object construction (JLS §17.5).ACC_VOLATILE0x0040Declared volatile; cannot be cached.ACC_TRANSIENT0x0080Declared transient; not written or read by a persistent object manager.ACC_SYNTHETIC0x1000Declared synthetic; not present in the source code.ACC_ENUM0x4000Declared as an element of an enum.Fields of classes may set any of the flags in Table 4.5-A. However, each field of a class may have at most one of its ACC_PUBLIC, ACC_PRIVATE, and ACC_PROTECTED flags set (JLS §8.3.1), and must not have both its ACC_FINAL and ACC_VOLATILE flags set (JLS §8.3.1.4).Fields of interfaces must have their ACC_PUBLIC, ACC_STATIC, and ACC_FINAL flags set; they may have their ACC_SYNTHETIC flag set and must not have any of the other flags in Table 4.5-A set (JLS §9.3).The ACC_SYNTHETIC flag indicates that this field was generated by a compiler and does not appear in source code.The ACC_ENUM flag indicates that this field is used to hold an element of an enumerated type.All bits of the access_flags item not assigned in Table 4.5-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) which represents a valid unqualified name denoting a field (§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 (§4.4.7) which represents a valid field descriptor (§4.3.2).

• attributes_count

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

• attributes[]

  Each value of the attributes table must be an attribute_info structure (§4.7).A field can have any number of optional attributes associated with it.The attributes defined by this specification as appearing in the attributes table of a field_info structure are listed in Table 4.7-C.The rules concerning attributes defined to appear in the attributes table of a field_info structure are given in §4.7.The rules concerning non-predefined attributes in the attributes table of a field_info structure are given in §4.7.1.

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