1 package day03;
 2 
 3 public class UpTest {
 4     public static void main(){
 5         Aoo o = new Aoo();
 6         o.a = 3;
 7         o.b = 3;  //錯誤,不能訪問子類成員
 8         
 9         Boo x = new Boo();
10         x.b = 3;
11         x.a = 3;
12         x.say();
13         
14         Aoo y = new Boo();  //
 
向上造型，父類引用指向子類對象
15         y.a = 3;
16         y.b = 3;
17         
18     }
19 }
20 
21 class Aoo{
22     int a;
23     void show(){
24     }
25 }
26 
27 class Boo extends Aoo{
28     int b;
29     void say(){}
30 }

父類、子類 ：繼承、向上造型。

java - day10 - uptest