interface overriding, overloading

http://java.sun.com/docs/books/jls/second_edition/html/interfaces.doc.html

9.4.3 Examples of Abstract Method Declarations

The following examples illustrate some (possibly subtle) points about abstract method declarations.

9.4.3.1 Example: Overriding

Methods declared in interfaces are abstract and thus contain no implementation. About all that can be accomplished by an overriding method declaration, other than to affirm a method signature, is to restrict the exceptions that might be thrown by an implementation of the method. Here is a variation of the example shown in §8.4.3.1:

class BufferEmpty extends Exception {

BufferEmpty() { super(); }

BufferEmpty(String s) { super(s); }

}

class BufferError extends Exception {

BufferError() { super(); }

BufferError(String s) { super(s); }

}

public interface Buffer {

char get() throws BufferEmpty, BufferError;

}

public interface InfiniteBuffer extends Buffer {

char get() throws BufferError; // override

}

9.4.3.2 Example: Overloading

In the example code:

interface PointInterface {

void move(int dx, int dy);

}

interface RealPointInterface extends PointInterface {

void move(float dx, float dy);

void move(double dx, double dy);

}

the method name move is overloaded in interface RealPointInterface with three different signatures, two of them declared and one inherited. Any non-abstract class that implements interface RealPointInterface must provide implementations of all three method signatures.