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The value of the access_flags item is a mask of flags used to denote access permissions to and properties of this class or interface. The interpretation of each flag, when set, is specified in .
Table 4.1-A. Class access and property modifiers
| Flag Name | Value | Interpretation |
|---|---|---|
ACC_PUBLIC | 0x0001 | Declared public; may be accessed from outside its package. |
ACC_FINAL | 0x0010 | Declared final; no subclasses allowed. |
ACC_SUPER | 0x0020 | Treat superclass methods specially when invoked by the invokespecial instruction. |
ACC_INTERFACE | 0x0200 | Is an interface, not a class. |
ACC_ABSTRACT | 0x0400 | Declared abstract; must not be instantiated. |
ACC_SYNTHETIC | 0x1000 | Declared synthetic; not present in the source code. |
ACC_ANNOTATION | 0x2000 | Declared as an annotation type. |
ACC_ENUM | 0x4000 | Declared as an enum type. |
An interface is distinguished by the ACC_INTERFACE flag being set. If the ACC_INTERFACE flag is not set, this class file defines a class, not an interface.
If the ACC_INTERFACE flag is set, the ACC_ABSTRACT flag must also be set, and the ACC_FINAL, ACC_SUPER, and ACC_ENUM flags set must not be set.
If the ACC_INTERFACE flag is not set, any of the other flags in may be set except ACC_ANNOTATION. However, such a class file must not have both its ACC_FINAL and ACC_ABSTRACT flags set (JLS §8.1.1.2).
The ACC_SUPER flag indicates which of two alternative semantics is to be expressed by the invokespecial instruction () if it appears in this class or interface. Compilers to the instruction set of the Java Virtual Machine should set the ACC_SUPER flag. In Java SE 8 and above, the Java Virtual Machine considers the ACC_SUPER flag to be set in every class file, regardless of the actual value of the flag in the class file and the version of the class file.
The ACC_SUPER flag exists for backward compatibility with code compiled by older compilers for the Java programming language. In JDK releases prior to 1.0.2, the compiler generated access_flags in which the flag now representing ACC_SUPER had no assigned meaning, and Oracle's Java Virtual Machine implementation ignored the flag if it was set.
The ACC_SYNTHETIC flag indicates that this class or interface was generated by a compiler and does not appear in source code.
An annotation type must have its ACC_ANNOTATION flag set. If the ACC_ANNOTATION flag is set, the ACC_INTERFACE flag must also be set.
The ACC_ENUM flag indicates that this class or its superclass is declared as an enumerated type.
All bits of the access_flags item not assigned in are reserved for future use. They should be set to zero in generated class files and should be ignored by Java Virtual Machine implementations.
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