package lesson;

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{}

public class duotai {

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));   //A and A  
    System.out.println(a1.show(c));   //A and A  
    System.out.println(a1.show(d));   //A and D
    System.out.println(a2.show(b));   //B and A  
    System.out.println(a2.show(c));   //B and A  
    System.out.println(a2.show(d));   //A and D 
    System.out.println(b.show(b));    //B and B 
    System.out.println(b.show(c));    //B and B 
    System.out.println(b.show(d));    //A and D    

}

}