1. public class TestA {

 2.    public void a(){System.out.print("1111 ");｝

 3.｝

 4.

 5.public class TestB extends TestA{

 6.    public void a(){System.out.print("2222 ");}

 7.        public static void main(String[] args) {

 8.           TestA a = new TestB();

 9.           TestB b = (TestB)a;

10.            a.a();

11.            b.a();

12.    ｝

13.｝

14.