1 public class Fu {
2     int num = 3;
3     void show() {
4         System.out.println("F1");
5     }
6     static void method() {
7         System.out.println("F2");
8     }
9 }

 1 public class Zi extends Fu{
 2     int sum = 4;
 3     
 4     void show() {
 5         System.out.println("Z1");
 6     }
 7     
 8     static void method() {
 9         System.out.println("Z2");
10     }
11 }

1 public class DouTaiDemo {
2     public static void main(String[] args) {
3         Fu f = new Zi();
4         System.out.println(f.num);
5         f.show();
6         f.method();
7     }
8     
9 }