继承与上转型对象·

import java.util.*;
        class A{
            int viar = 7;
            void m1(){
                System.out.println("A's m1,");
            }
            void m2(){
                System.out.println("A's m2,");
            }
            void m3(){
                System.out.println("A's m3,");
            } }
        class B extends A{
            void m1(){
                System.out.println("B's m1,");
            } }
        class C extends B{
            void m3(){
                System.out.println("C's m3," + (viar + 6));
            }
        }

public class Main {
    public static void main(String[] args) {
        A a = new A();
        B b = new B();
        C c = new C();
        A a2 = new C();
        b.m1();//B's m1,
        c.m2();//A's m2,
        a.m3();//A's m3,
        c.m1();//B's m1,
        c.m2();//A's m2,
        c.m3();//C's m3,13
        a.m1();//A's m1,
        b.m2();//A's m2,
        c.m3();//C's m3,13
        a2.m1();//A's m1,此处当时想错
        a2.m2();//A's m2,此处当时想错
        a2.m3();//A's m3,此处当时想错

    }
}


结果：

B's m1,
A's m2,
A's m3,
B's m1,
A's m2,
C's m3,13
A's m1,
A's m2,
C's m3,13
B's m1,
A's m2,
C's m3,13