9.4 Abstract Method Declarations

AbstractMethodDeclaration:

	AbstractMethodModifiersopt ResultType MethodDeclarator Throwsopt ;

AbstractMethodModifiers:

	AbstractMethodModifier

	AbstractMethodModifiers AbstractMethodModifier

AbstractMethodModifier: one of

	public abstract

The access modifier public is discussed in §6.6. A compile-time error occurs if the same modifier appears more than once in an abstract method declaration.

Every method declaration in the body of an interface is implicitly abstract, so its body is always represented by a semicolon, not a block. For compatibility with older versions of Java, it is permitted but discouraged, as a matter of style, to redundantly specify the abstract modifier for methods declared in interfaces.

Every method declaration in the body of an interface is implicitly public. It is permitted, but strongly discouraged as a matter of style, to redundantly specify the public modifier for interface methods.

Note that a method declared in an interface must not be declared static, or a compile-time error occurs, because in Java static methods cannot be abstract.

Note that a method declared in an interface must not be declared native or synchronized, or a compile-time error occurs, because those keywords describe implementation properties rather than interface properties. However, a method declared in an interface may be implemented by a method that is declared native or synchronized in a class that implements the interface.

Note that a method declared in an interface must not be declared final or a compile-time error occurs. However, a method declared in an interface may be implemented by a method that is declared final in a class that implements the interface.