原型模式(prototype)

意图: 用原型实例指定创建对象的种类，并通过拷贝这些原型创建新的对象。
结构图

实现示例：
原型Prototype:

public abstract class Prototype implements Cloneable {
	public abstract void show();
	protected Object clone() throws CloneNotSupportedException {
		return super.clone();
	}
}

Prototype子类：

public class ConcretePrototype1 extends Prototype {

	private String description;
	
	public void setDescription(String description) {
		this.description = description;
	}
	@Override
	public void show() {
		System.out.println("Concrete 1 description: " + description);
	}

	@Override
	protected Object clone() throws CloneNotSupportedException {
		Object o = super.clone();
		if (this.description == null) {
			((ConcretePrototype1) o).description = this.description;
		}
		return o;
	}
}

public class ConcretePrototype2 extends Prototype {

	private int flag;
	
	public void setFlag(int flag) {
		this.flag = flag;
	}
	@Override
	public void show() {
		// TODO Auto-generated method stub
		System.out.printf("Concrete 2 flag = %d\n", flag);
	}

	@Override
	protected Object clone() throws CloneNotSupportedException {
		Object o = super.clone();
		if (this.flag != 0) {
			((ConcretePrototype2) o).flag = this.flag;
		}
		return o;
	}
}

客户端使用：

import java.util.Enumeration;
import java.util.Vector;

public class Container {
	private Vector vector;
	public Container() {
		vector = new Vector();
	}
	
	public void addItem(Prototype item) {
		vector.addElement(item);
		System.out.println("Now items list:");
		Enumeration enumeration = vector.elements();
		while (enumeration.hasMoreElements()) {
			Prototype t = (Prototype)enumeration.nextElement();
			t.show();
		}
	}
}

public class Client {
	private Prototype prototype;
	
	public void setPrototype(Prototype prototype) {
		this.prototype = prototype;
	}
	
	public void runExample() throws Exception {
		Container c = new Container();
		ConcretePrototype1 item1 = null;
		item1 = (ConcretePrototype1)prototype.clone();
		item1.setDescription("this is item1");
		c.addItem(item1);
		
		ConcretePrototype1 item2 = null;
		item2 = (ConcretePrototype1)item1.clone();
		item2.setDescription("This is item2");
		c.addItem(item2);
		
		ConcretePrototype2 item3 = null;
		item3 = new ConcretePrototype2();
		item3.setFlag(100);
		c.addItem(item3);
		
		ConcretePrototype2 item4 = null;
		item4 = (ConcretePrototype2)item3.clone();
		item4.setFlag(500);
		c.addItem(item4);
	}
	
	public static void main(String args[]) throws Exception {
		Client client = new Client();
		client.setPrototype(new ConcretePrototype1());
		client.runExample();
	}
}

执行结果：
Now items list:
Concrete 1 description: this is item1
Now items list:
Concrete 1 description: this is item1
Concrete 1 description: This is item2
Now items list:
Concrete 1 description: this is item1
Concrete 1 description: This is item2
Concrete 2 flag = 100
Now items list:
Concrete 1 description: this is item1
Concrete 1 description: This is item2
Concrete 2 flag = 100
Concrete 2 flag = 500

注：示例中原型Prototype只有一个属性，通过复制来创建没有体现其优势，当prototype中属性较多时，通过复制可以节省初始化的开销