怎么理解？
package com.duotai.test;
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{}
package com.duotai.test;
public class TestA {
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));
System.out.println(a1.show(c));
System.out.println(a1.show(d));
System.out.println("***************");
System.out.println(a2.show(b));
System.out.println(a2.show(c));
System.out.println(a2.show(d));
System.out.println("***************");
System.out.println(b.show(b));
System.out.println(b.show(c));
System.out.println(b.show(d));
}
}
结果是：A and A
A and A
A and D
***************
B and A
B and A
A and D
***************
B and B
B and B
A and D
