java多態例子

標籤：

多態存在的三個必要條件
一、要有繼承；
二、要有重寫；
三、父類引用指向子類對象。

代碼部分：

class A {    public String show(D obj) {        return ("A and D");    }    public String show(A obj) {        return ("A and A");    }}class B extends A {    public String show(B obj) {        return ("B and B");    }    public String show(A obj) {        return ("B and A");    }}class C extends B {}class D extends B {}

然後開始搞腦子了：

public static void main(String[] args) {        A a1 = new A();        A a2 = new B();        B b = new B();        C c = new C();        D d = new D();                System.out.println(a1.show(a1));        System.out.println(a1.show(a2));        System.out.println(a2.show(a1));        System.out.println(a2.show(a2));        System.out.println(b.show(a1));        System.out.println(b.show(a2));        System.out.println(c.show(a1));        System.out.println(c.show(a2));        System.out.println(d.show(a1));        System.out.println(d.show(a2));        System.out.println("分割線**************************************");        System.out.println(a1.show(b));        System.out.println(a1.show(c));        System.out.println(a1.show(d));        System.out.println(a2.show(b));        System.out.println(a2.show(c));        System.out.println(a2.show(d));        System.out.println(b.show(b));        System.out.println(b.show(c));        System.out.println(b.show(d));        System.out.println(c.show(b));        System.out.println(c.show(c));        System.out.println(c.show(d));    }

運行結果：

A and AA and AB and AB and AB and AB and AB and AB and AB and AB and A分割線**************************************A and AA and AA and DB and AB and AA and DB and BB and BA and DB and BB and BA and D

為了方便理解，我列了下每個類的method table

Ashow(D) -> A.show(D)show(A) -> A.show(A)B，C, Dshow(D) -> A.show(D)show(B) -> B.show(B)show(A) -> B.show(A)

 

java多態例子