例題 計算機連線各種外設，每個外設都有各自的讀寫方法 目的實現程式碼依賴介面，而不是依賴具體的類，方便程式的擴充套件

package Computer;
public interface IMobleDevice{
	public void write();
	public void read();
}
=====================================================
package Computer;

public class Computer {
	IMobleDevice device;

	public Computer() {
		super
 
();
	}

	public Computer(IMobleDevice device) {
		super();
		this.device = device;
	}

	public IMobleDevice getDevice() {
		return device;
	}

	public void writeData() {
		device.write();
	}

	public void readDate() {
		device.read();
	}

	public void setDevice(IMobleDevice device) {
		this.device =
 
 device;
	}

}
=====================================================
package Computer;

public class Phone implements IMobleDevice {
	public void write() {
		System.out.println("把筆記本資料寫入手機");
	}
	public void read() {
		System.out.println("從手機讀取資料到筆記本");
	}

}
========================================
 
=============
package Computer;

public class UDisk implements IMobleDevice {
	public void write() {
		System.out.println("寫入U盤");
	}
	public void read() {
		System.out.println("讀取U盤");
	}

}

=====================================================
package Computer;

public class MobileHarddisk implements IMobleDevice {
	public void write() {
		System.out.println("把資料寫入行動硬碟");
	}
	public void read() {
		System.out.println("從行動硬碟讀取資料");
	}

}
=====================================================

package Computer;

public class RunningDemo {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Computer computer =new Computer();
		UDisk disk=new UDisk();
		computer.setDevice(disk);//新增一個具體的多型介面
		computer.readDate();
		computer.writeData();
		Phone phone=new Phone();
		computer.setDevice(phone);//修改新增的資料
		computer.readDate();
		computer.writeData();
		MobileHarddisk harddisk=new MobileHarddisk();
		computer.setDevice(harddisk);
		computer.readDate();
		computer.writeData();
	}

}