java一个简单小程序，求高手帮忙编写，万分感谢

class Ball {

public void play() {

System.out.println("玩球儿...");

}

}

class Football extends Ball {

public void play() {

System.out.println("使用足球运动");

}

}

class Basketball extends Ball {

public void play() {

System.out.println("使用篮球运动");

}

}

public class TestMain {

public static void main(String[] args) {

TestMain tm = new TestMain();

tm.testPlay();

}

public void testPlay() {

Ball ball = new Football();

ball.play();

ball = new Basketball();

ball.play();

}

}

/*

D:\>javac TestMain.java

D:\>java TestMain

使用足球运动

使用篮球运动

*/