Java学习笔记——设计模式之六.原型模式（浅克隆和深克隆）

 That there's some good in this world, Mr. Frodo. And it's worth fighting for.

 

原型模式（prototype），用原型实例指定创建对象的种类，并且通过拷贝这些原型创建新的对象。

至于Object.clone()这里就不赘述了。文档看起来可能有些难懂，直接上代码反而更容易理解：

浅克隆：

package cn.happy.design_pattern._06prototype.shallowclone;

public abstract class Prototype {

    private String id;

    String getId() {
        return id;
    }

    void setId(String id) {
        this.id = id;
    }
    
    public abstract Prototype mClone();
}

package cn.happy.design_pattern._06prototype.shallowclone;

public class ConcretePrototype extends Prototype implements Cloneable{

    private Obj obj;
    public ConcretePrototype() {
        super();
        obj = new Obj();
    }

    /*
     * getter and setter
     */
    Obj getObj() {
        return obj;
    }


    void setObj(Obj obj) {
        this.obj = obj;
    }


    @Override
    public Prototype mClone() {
        // TODO Auto-generated method stub
        Prototype prototype = null;
        try {
            prototype = (Prototype)this.clone();
        } catch (CloneNotSupportedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return prototype; 
    }

}

package cn.happy.design_pattern._06prototype.shallowclone;

public class Obj {

    private String name;

    String getName() {
        return name;
    }

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

package cn.happy.design_pattern._06prototype.shallowclone;

public class Mmain {

    public static void main(String[] args) {
        ConcretePrototype c1 = new ConcretePrototype();
        ConcretePrototype c2 = (ConcretePrototype)c1.mClone();
        c1.setId("原型");
        c1.getObj().setName("张三");
        c2.setId("副本");
        c2.getObj().setName("李四");
        /*
         *  浅克隆：
         *  Id是值类型变量，逐位复制，产生新的变量地址；Obj是引用变量，只复制引用，副本和原型共享同一变量地址；
         *  输出：prototype.shallowclone.ConcretePrototype@15db9742,原型,李四
         *       prototype.shallowclone.ConcretePrototype@6d06d69c,副本,李四
         */
        System.out.println(c1+","+c1.getId()+","+c1.getObj().getName());
        System.out.println(c2+","+c2.getId()+","+c2.getObj().getName());

    }

}

这里需要提下两种特殊的值类型变量，字符串（其实字符串底层是char数组）和数组。它们虽然是引用类型但是可被浅克隆。大家一试便知。

深克隆：

Prototype 类不变。

package cn.happy.design_pattern._06prototype.deepclone;

public class ConcretePrototype extends Prototype implements Cloneable{

    private Obj obj;
    public ConcretePrototype() {
        super();
        obj = new Obj();
    }
    //添加新的构造方法
    private ConcretePrototype(Obj obj) {
        super();
        this.obj = (Obj) obj.mClone();
    }


    /*
     * getter and setter
     */
    Obj getObj() {
        return obj;
    }


    void setObj(Obj obj) {
        this.obj = obj;
    }


    @Override
    public Prototype mClone() {
        // TODO Auto-generated method stub
        Prototype prototype = null;
        //调用新的构造方法
        prototype = new ConcretePrototype(getObj());
        prototype.setId(getId());
        return prototype; 
    }

}

package cn.happy.design_pattern._06prototype.deepclone;

public class Obj implements Cloneable{
　　//省略属性，这里也许需要更深层克隆。
    public Object mClone(){
        Obj obj = null;
        try {
            obj = (Obj)this.clone();
        } catch (CloneNotSupportedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return obj;
    }
}

测试类：

package cn.happy.design_pattern._06prototype.deepclone;

public class Mmain {

    public static void main(String[] args) {
        ConcretePrototype c1 = new ConcretePrototype();
        ConcretePrototype c2 = (ConcretePrototype)c1.mClone();
        /*
         *  深克隆：c1与c2中Obj的地址不同了
         *  输出：...ConcretePrototype@15db9742,null,...Obj@6d06d69c
         *       ...ConcretePrototype@7852e922,null,...Obj@4e25154f
         */
        System.out.println(c1+","+c1.getId()+","+c1.getObj());
        System.out.println(c2+","+c2.getId()+","+c2.getObj());

    }

}