java 多态性举例来说

java 多态性举例

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自己比较懒，上次面试遇到这个问题，回来查了下。网上查了，大概有这两种例子。
1.一种是普通的超类，子类覆盖父类的方法。
2.父类是抽象类，子类实现父类的抽象方法。

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1.网上摘抄：

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Game类是Football、Basketball、Popolong的父类，Games类使用前面4个类。

Java根据动态绑定决定执行“更具体”的方法，即子类方法。

//Game.java
1. package?cn.edu.uibe.oop;
2. public?class?Game?{
3. ?protected?void?play(){??System.out.println("play?game");
4. ?}
5. }
6. //Football.java
7. package?cn.edu.uibe.oop;
8. public?class?Football?extends?Game?{
9. ?protected?void?play()?{????System.out.println("play?football");
10. ????super.play();?}
11. ?void?f(){??play();
12. ?}}
14. //Basketball.java
15. package?cn.edu.uibe.oop;
16. public?class?Basketball?extends?Game{
17. ?protected?void?play()?{
18. ??System.out.println("play?basketball");?}
19. }
21. //Popolong.java
22. package?cn.edu.uibe.oop;
23. public?class?Popolong?extends?Game?{
24. ?protected?void?play()?{??System.out.println("play?popolong");
25. ?}
26. }
27. //Games.java
28. package?cn.edu.uibe.oop;
29. public?class?Games?{
30. ?public?static?void?main(String[]?args)?{
31. ??Game[]?games?=?new?Game[10];??games[0]?=?new?Basketball();
32. ??games[1]?=?new?Football();??games[2]?=?new?Popolong();
33. ????for(int?i=0;i<games.length;i++){
34. ???if(games[i]!=null)??????games[i].play();
35. ??}??
36. ?}
37. }

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2.from network

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如在计算公司雇员工资的超类中

????? ??? // 用抽象方法作为多态接口?
??? public abstract class Employee {?
??????? ...?
??????? public abstract double earnings();??? //定义抽象方法作为多态接口?
??? }
//这个方法将作为多态接口被子类的方法所覆盖?
??? public class Manager extends Employee {?
??? ...?
??? public double eamings () return 0.0;

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??? 抽象方法也可用protected.

1. public?class?CircleShapeApp{ ?????public?static?void?main(String[]?args)?{ ?
2. ????????Circle?circle?=?new?Circle(12.98); ?????????Sphere?sphere?=?new?Sphere(25.55); ?
3. ? ?????????Shape?shape?=?circle;???????//向上转型 ?
4. ????????//多态调用 ?????????shape.computeArea(); ?
5. ????????shape.computeVolume(); ?????????System.out.println("circle?area:?"?+?shape.getArea()); ?
6. ????????System.out.println("circle?volume:?"?+?shape.getVolume()); ?????????//多态调用 ?
7. ????????shape?=?sphere; ?????????shape.computeArea(); ?
8. ????????shape.computeVolume(); ?????????System.out.println("Sphere?area:?"?+?shape.getArea()); ?
9. ????????System.out.println("Sphere?volume:?"?+?shape.getVolume()); ?????} ?
10. }