課本例題5.2

abstract class GirlFriend() {
abstract void speak();
abstract void cooking();

}
class ChinaGirlFriend extends GirlFriend() {
void speak() {
System.out.println("你好");
}
void cooking() {
System.out.println("水煮魚");
}
}
class AmericanGirlFriend extends GirlFriend() {
void speak() {
System.out.println("hello");
}
void cooking() {
System.out.println("roast beef");
}
}
class Boy{
GirlFriend friend ;
void setGrilFriend(GirlFriend f) {
friend = f;
}
void showGirlFriend() {
friend.speak();
friend.cooking();
}
}
public class Example5_2 {


public static void main(String[] args) {
// TODO Auto-generated method stub
GirlFriend girl = new ChinaGirlFriend();
Boy boy = new Boy();
boy.setGrilFriend(girl);
boy.showGirlFriend();
girl = new AmericanGirlFriend() ;
boy.setGrilFriend(girl);
boy.showGirlFriend();




}


}