emptyballlist.java

书籍"Java_面向事件编程"的附带光盘代码

import objectdraw.*;

// An empty list of balls.  This implements the ball list
// interface, but only the isEmpty method should be used.

public class EmptyBallList implements BallListInterface {
    
    public EmptyBallList() {}
    
    public boolean isEmpty() {
        return true;
    }
    
    // return null as a default value
    public FilledOval getFirst() {
        return null;
    }
    
    // return null as a default value
    public BallListInterface getRest() {
        return null;
    }
    
}