java - day10 - uptest
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; //错误,不能访问子类成员 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，父类引用指向子类对象 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 }
父类、子类 ：继承、向上造型。
