jvm-Access Flag

Access Flagsin the previous analysis of the class file's magic number, minor version number, major version number, constant pool entrance, constant pool, then after the constant pool ends, immediately after the two bytes represents the access flag (access_flages). This flag is used to identify some class or interface-level access information, including: Whether this class is an interface, is defined as a public type, is defined as an abstract type, and if it is a class, it is declared final, and so on. The access flags and their meanings are as follows:

　　

Flag Name	Flag value	Meaning
Acc_public	0x00 01	is public type
Acc_final	0x00 10	is declared final, only the class can set the
Acc_super	0x00 20	Whether to allow the use of the new semantics of invokespecial bytecode directives.
Acc_interface	0x02 00	Flag this is an interface
Acc_abstract	0x04 00	is an abstract type, the secondary flag value is true for interfaces or abstract classes, and other types are false
Acc_synthetic	0x10 00	Flag This class is not generated by user code
Acc_annotation	0x20 00	Flag this is an annotation
Acc_enum	0x40 00	Flag This is an enumeration

Access_flages The CCP has two bytes (16 bits) can be used, no use of the logo for the requirements are all 0.

Next, continue to analyze the previous example:

Source:

 class file:

　　In this diagram, after the constant pool, the access flags are analyzed.

The analysis of 0x00 01 and 0x00 20 is through the above access to the sign table, corresponding to the Acc_public and Acc_super. Since only the two flag bits are 1, the other flag bits are 0, the values of each flag and the value of the flag itself are followed, and then the value of the entire access flag can be calculated. 0x00 01 | 0x00 = 0x00 21.

jvm-Access Flag