CLASSES

Superinterfaces

8.1.4

Thus, the example:

interface Colorable {

void setColor(int color);

int getColor();

}

class Point { int x, y; };

class ColoredPoint extends Point implements Colorable {

int color;

}

causes a compile time error, because

ColoredPoint

 is not an

abstract

 class but

it fails to provide an implementation of methods

setColor

 and

getColor

 of the

interface

Colorable

.

It is permitted for a single method declaration in a class to implement methods

of more than one superinterface. For example, in the code:

interface Fish { int getNumberOfScales(); }

interface Piano { int getNumberOfScales(); }

class Tuna implements Fish, Piano {

//

You can tune a piano, but can you tuna fish?

int getNumberOfScales() { return 91; }

}

the method

getNumberOfScales

 in class

Tuna

 has a name, signature, and return

type that matches the method declared in interface

Fish

 and also matches the

method declared in interface

Piano

; it is considered to implement both.

On the other hand, in a situation such as this:

interface Fish { int getNumberOfScales(); }

interface StringBass { double getNumberOfScales(); }

class Bass implements Fish, StringBass {

//

This declaration cannot be correct, no matter what type is used.

public

???

 getNumberOfScales() { return 91; }

}

it is impossible to declare a method named

getNumberOfScales

 with the same

signature and return type as those of both the methods declared in interface

Fish

and in interface

StringBass

, because a class can have only one method with a

given signature ( 8.4). Therefore, it is impossible for a single class to implement

both interface

Fish

 and interface

StringBass

 ( 8.4.6).

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