Interfaces and Inner Classes - Absolute Java - page 716

Display 13.3 An Abstract Class Implementing an Interface ★

1 public abstract class MyAbstractClass implements Ordered
2 {
3 private int number;
4 private char grade;
5
6 public boolean precedes(Object other)
7 {
8 if (other == null )
9 return false ;
10 else if (!(other instanceof HourlyEmployee))
11 return false ;
12 else
13 {
14 MyAbstractClass otherOfMyAbstractClass =
15 (MyAbstractClass)other;
16 return ( this .number < otherOfMyAbstractClass.number);

17 }
18 }

19 public abstract boolean follows(Object other);

20 }

Display 13.4 Extending an Interface

1 public interface ShowablyOrdered extends Ordered
2 {
3

/**

4 Outputs an object of the class that precedes the calling object.

5 */

6 public void showOneWhoPrecedes();

7 }

Neither the compiler nor the run-time system
will do anything to ensure that this comment is
satisfied.

A (concrete) class that implements the ShowablyOrdered interface must have a
definition for the method showOneWhoPrecedes and also have definitions for the
methods precedes and follows given in the Ordered interface.