从原型模式(Prototype Pattern)到 Clone

前面提到抽象工厂的实现,这里说说抽象工厂的原型实现,与工厂方法的实现不同,原型实现有他自己的优点和缺点

原型的优点:

1. 效率:clone是native方法,比new的效率高,当使用复杂循环嵌套对象是尤为明显

2. 不需要为每一个新增的product创造一个具体factory

缺点:

1. 如果需要深复制,则需要手写所有包含循环引用对象的类的clone方法,因为需要手动在clone方法里对引用对象进行clone,否则是浅复制

2. 当需要改变一个克隆实例内部的值时,由于clone方法是无参方法,只能在clone完以后手动调用改变值得方法,且如果这个值是一个类的引用,则克隆应该建立在深复制的前提下,否则会污染原型数据

3. 原型工厂有可能被初始化成不兼容组件的组合,例如 CatHead和DogBody的组合,实际上这也是原型的一个灵活性的体现之一

4. 就Java而言,它的clone方法是protected方法,我们需要手动实现Clonable接口以后重写clone()方法将其改为public方法才能调用

下面是一个例子

工厂类,不在需要具体的工厂子类,而是通过构造方法设置原型来产生不同的工厂

package factory;

import product.Body;
import product.Eye;
import product.Head;

/**
 * Created with IntelliJ IDEA.
 * User: zhenwei.liu
 * Date: 13-8-1
 * Time: 上午12:33
 * To change this template use File | Settings | File Templates.
 */
public class ModuleFactory {
    private static ModuleFactory factory = new ModuleFactory();
    private static Head _head;   // 原型组件
    private static Body _body;
    private static Object lockObj = new Object();

    // 设置原型
    public static ModuleFactory createFactory(Head newHead, Body newBody) {
        if (newHead == null || newBody == null)
            throw new RuntimeException("Param newHead and newBody cannot be null");

        // 为简单起见,不考虑多线程问题,不使用延迟加载
        _head = newHead;
        _body = newBody;

        return factory;
    }

    public Head createHead() throws CloneNotSupportedException {
        Head head = (Head) _head.clone();
        return head;
    }

    // 重载方法
    public Head createHead(Eye eye) throws CloneNotSupportedException {
        Head head = (Head) _head.clone();
        // 必须在clone之后手动调用修改成员的方法
        head.setEye(eye);
        return head;
    }

    public Body createBody() throws CloneNotSupportedException {
        return (Body) _body.clone();
    }
}

产品类

package product;

/**
 * Created with IntelliJ IDEA.
 * User: zhenwei.liu
 * Date: 13-8-1
 * Time: 上午12:24
 * To change this template use File | Settings | File Templates.
 */
public abstract class Head implements Cloneable {
    private Eye eye = new Eye("defaultEye");

    public Eye getEye() {
        return eye;
    }

    public void setEye(Eye eye) {
        this.eye = eye;
    }

    @Override
    public Object clone() throws CloneNotSupportedException {
        Head head = (Head) super.clone();
        // 对内部对象进行深复制
        head.setEye((Eye) eye.clone());
        return head;
    }

    public abstract void eat();
}

package product;

/**
 * Created with IntelliJ IDEA.
 * User: zhenwei.liu
 * Date: 13-8-1
 * Time: 上午12:29
 * To change this template use File | Settings | File Templates.
 */
public class DogHead extends Head {
    @Override
    public void eat() {
        System.out.println("A dooog's head is eating with its eye " + getEye().getName());
    }
}

package product;

/**
 * Created with IntelliJ IDEA.
 * User: zhenwei.liu
 * Date: 13-8-1
 * Time: 上午12:29
 * To change this template use File | Settings | File Templates.
 */
public class CatHead extends Head {
    @Override
    public void eat() {
        System.out.println("A caaat's head is eating fast");
    }
}

package product;

/**
 * Created with IntelliJ IDEA.
 * User: zhenwei.liu
 * Date: 13-8-1
 * Time: 上午12:48
 * To change this template use File | Settings | File Templates.
 */
public class Eye implements Cloneable{
    private String name;

    @Override
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }

    public Eye(String name) {
        this.name = name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

package product;

/**
 * Created with IntelliJ IDEA.
 * User: zhenwei.liu
 * Date: 13-8-1
 * Time: 上午12:24
 * To change this template use File | Settings | File Templates.
 */
public abstract class Body implements Cloneable {
    public abstract void dance();

    // 此处必须将clone方法重新声明为public方法
    @Override
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

package product;

/**
 * Created with IntelliJ IDEA.
 * User: zhenwei.liu
 * Date: 13-8-1
 * Time: 上午12:27
 * To change this template use File | Settings | File Templates.
 */
public class CatBody extends Body {
    @Override
    public void dance() {
        System.out.println("A caaat's body is dancing crazily!!");
    }
}

package product;

/**
 * Created with IntelliJ IDEA.
 * User: zhenwei.liu
 * Date: 13-8-1
 * Time: 上午12:27
 * To change this template use File | Settings | File Templates.
 */
public class DogBody extends Body {
    @Override
    public void dance() {
        System.out.println("A dooog's body is dancing!");
    }
}

测试类

import factory.ModuleFactory;
import product.*;

/**
 * Created with IntelliJ IDEA.
 * User: zhenwei.liu
 * Date: 13-8-1
 * Time: 上午12:35
 * To change this template use File | Settings | File Templates.
 */
public class Test {

    // 通过原型工厂克隆得到新的实例
    // 与具体实现无关的解耦代码
    private static void act(ModuleFactory factory) throws CloneNotSupportedException {
        Head head = factory.createHead();
        Body body = factory.createBody();
        head.eat();
        body.dance();
    }

    public static void main(String[] args) throws CloneNotSupportedException {
        Head head = new DogHead();
        head.getEye().setName("customEye");
        ModuleFactory factory = ModuleFactory.createFactory(head, new DogBody());
        factory.createHead().eat();

        // 测试深浅复制
        Head head2 = (Head) head.clone();
        head2.getEye().setName("smallEye");
        head2.eat();
        head.eat(); // 这里的输出发现eye并没有变成smallEye,所以可以确定eye是深复制

        System.out.println();
        factory = ModuleFactory.createFactory(new CatHead(), new CatBody());
        act(factory);
    }
}

输出

A dooog's head is eating with its eye customEye
A dooog's head is eating with its eye smallEye
A dooog's head is eating with its eye customEye

A caaat's head is eating fast
A caaat's body is dancing crazily!!