多态的示例

需求：电脑运行实例，电脑运行基于主板

 

//接口
interface PCI
{
	public void open();
	public void close();
}

class MainBoard 
{
	public void run()
	{
		System.out.println("mainboard run");
	}
	public void usePCI(PCI p)//PCI p = new Netcard(); 接口型引用指向自己的子类对象
	{
		if(p!=null)
		{
			p.open();
			p.close();
		}
	}
}

class NetCard  implements PCI
{
	public void open()
	{
		System.out.println("netcard open");
	}
	public void close()
	{
		System.out.println("netcard close");
	}
}

class SoundCard implements PCI
{
	public void open()
	{
		System.out.println("SoundCard open");
	}
	public void close()
	{
		System.out.println("SoundCard close");
	}
}

class DuotaiDemo
{
	public static void main(String[] args)
	{
		MainBoard mb = new MainBoard();
		mb.run();
		mb.usePCI(new NetCard());
		mb.usePCI(null);	
	}
}