sample5_9.java

封装

class Fruit
{ }
// Apple类是Fruit类的子类
class Apple extends Fruit
{ }
public class Sample5_9
{
	public static void main(String[] args)
	{
		//创建对象并将引用相互赋值
		Apple a=new Apple();
		//将子类引用a赋给父类引用f
		Fruit f=a;
		//将父类引用f赋给子类引用a
		a=f;
	}
}