【java開發系列】—— 深克隆和淺克隆

　　Java支持我們對一個對象進行克隆，通常用在裝飾模式和原型模式中。那么什么是深克隆，什么是淺克隆呢。

　　【淺克隆】，通常只是對克隆的實例進行復制，但里面的其他子對象，都是共用的。

　　【深克隆】，克隆的時候會復制它的子對象的引用，里面所有的變量和子對象都是又額外拷貝了一份。

　　下面的兩個例子可以很好的說明他們的區別：

　　首先看一下類圖

　　Husband類有一個對wife的引用，當進行淺克隆的時，wife變量都會指向同一個Wife；而進行深克隆時，會指向不同的Wife。下面進行一下驗證：

　　【淺克隆】

public Object clone() {
        Husband husband = null;
        try{
            husband = (Husband)super.clone();
        }catch(CloneNotSupportedException e){
            e.printStackTrace();
        }finally{
            return husband;
        }
    }

　　【深克隆】

public Object deepClone() throws IOException,ClassNotFoundException {
        //將對象寫到流里
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(bos);
        oos.writeObject(this);
        //從流里讀回來
        ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
        ObjectInputStream ois = new ObjectInputStream(bis);
        return ois.readObject();
    }

　　【全部代碼】

package com.xingoo.clone;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Date;

class Wife implements Serializable{
    private String name;
    private Date birthday;
    
    public Wife(){
        name = "芙蓉姐姐";
        birthday = new Date();
    }
    public Date getBirthday(){
        return birthday;
    }
    
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}
class Husband implements Cloneable,Serializable{
    private Wife wife;
    private Date birthday;
    
    public Husband(){
        wife = new Wife();
        birthday = new Date();
    }
    
    public Wife getWife(){
        return wife;
    }
    
    public Date getBirthday(){
        return birthday;
    }
    /**
     * 淺克隆一個對象
     */
    public Object clone() {
        Husband husband = null;
        try{
            husband = (Husband)super.clone();
        }catch(CloneNotSupportedException e){
            e.printStackTrace();
        }finally{
            return husband;
        }
    }
    /**
     * 利用串行化深克隆一個對象，把對象以及它的引用讀到流里，在寫入其他的對象
     * @return
     * @throws IOException
     * @throws ClassNotFoundException
     */
    public Object deepClone() throws IOException,ClassNotFoundException {
        //將對象寫到流里
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(bos);
        oos.writeObject(this);
        //從流里讀回來
        ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
        ObjectInputStream ois = new ObjectInputStream(bis);
        return ois.readObject();
    }
}
public class Test {
    public static void main(String[] args){
        try{
            Husband husband = new Husband();
            System.out.println("husband birthday "+husband.getBirthday().getTime());
            System.out.println("wife birthday "+husband.getWife().getBirthday().getTime());
            System.out.println();
            Husband husband1 = (Husband)husband.clone();
            System.out.println("husband1 birthday "+husband1.getBirthday().getTime());
            System.out.println("wife birthday "+husband1.getWife().getBirthday().getTime());
            System.out.println();
            System.out.println("是否是同一個husband "+(husband == husband1));
            System.out.println("是否是同一個wife "+ (husband.getWife() == husband1.getWife()));
            System.out.println();
            Husband husband2 = (Husband)husband.deepClone();
            System.out.println("husband2 birthday "+husband2.getBirthday().getTime());
            System.out.println("wife birthday "+husband2.getWife().getBirthday().getTime());
            System.out.println();
            System.out.println("是否是同一個husband "+(husband == husband2));
            System.out.println("是否是同一個wife "+ (husband.getWife() == husband2.getWife()));
        }catch(Exception e){
            e.printStackTrace();
        }
    }
}

　　【運行結果】

husband birthday 1414247244668
wife birthday 1414247244668

husband1 birthday 1414247244668
wife birthday 1414247244668
是否是同一個husband false
是否是同一個wife true

husband2 birthday 1414247244668
wife birthday 1414247244668
是否是同一個husband false
是否是同一個wife false