INTERFACES

Inheritance and Overriding

9.4.1

9.4   Abstract Method Declarations

AbstractMethodDeclaration:

AbstractMethodModifiers

opt

ResultType MethodDeclarator Throws

opt

 ;

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.

9.4.1   Inheritance and Overriding

If the interface declares a method, then the declaration of that method is said to

override

 any and all methods with the same signature in the superinterfaces of the

interface that would otherwise be accessible to code in this interface.

If a method declaration in an interface overrides the declaration of a method

in another interface, a compile time error occurs if the methods have different

return types or if one has a return type and the other is

void

. Moreover, a method

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