Java中多态的实例

 public class cf {

     /**
      * 实际上这里涉及方法调用的优先问题，
      * 优先级由高到低依次为：this.show(O)、super.show(O)、this.show((super)O)、super.show((super)O)。
      */
     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(b)); // ① A and A
         System.out.println(a1.show(c)); // ② A and A
         System.out.println(a1.show(d)); // ③ A and D
         System.out.println(a2.show(b)); // ④ B and A
         System.out.println(a2.show(c)); // ⑤ B and A
         System.out.println(a2.show(d)); // ⑥ A and D
         System.out.println(b.show(b)); // ⑦ B and B
         System.out.println(b.show(c)); // ⑧ B and B
         System.out.println(b.show(d)); // A and D
     }
 }

 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 {
 }

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