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@[toc] 无论是在java面试过程中，还是在与各种老鸟交流的过程中，对java对象的深浅拷贝，都是一个绕不开的问题，这个问题看似很容易，却是大多数人用来区分小白的标准问题。现在对该问题进行说明。

1.定义

浅克隆（拷贝）：复制一个对象的实例，但是这个对象中包含的其它的对象还是共用的。一般用super.clone()方法，clone的对象就是浅克隆。 深克隆（拷贝）：复制一个对象的实例，而且这个对象中包含的其它的对象也要复制一份。如果使用clone()，那么需要对clone方法进行重写，复制一个对象super.clone()，之后再一一对属性进行复制。这样显得非常冗余，幸好，在java中还可以通过流来实现。但是注意，对象需要实现Serializable接口。

2.举例

有如下类Husband, Husband又引用了Wife。

package com.dhb.CloneTest;

import lombok.Data;

import java.io.Serializable;
import java.util.Date;

@Data
public class Wife implements Serializable {

    private String name;

    private Date birthday;

    public Wife() {
        this.name = "思思";
        this.birthday = new Date();
    }

    public Wife(String name, Date birthday) {
        this.name = name;
        this.birthday = birthday;
    }
}

Husband类

package com.dhb.CloneTest;

import lombok.Data;

import java.io.*;
import java.util.Date;

@Data
public class Husband implements Cloneable,Serializable {

    private Wife wife;

    private Date birthday;

    public Husband() {
        this.wife = new Wife();
        this.birthday = new Date();
    }

    public Husband(Wife wife, Date birthday) {
        this.wife = wife;
        this.birthday = birthday;
    }

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

    public Object  deepClone() throws IOException, ClassNotFoundException {
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(bos);
        oos.writeObject(this);
        ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
        ObjectInputStream ois = new ObjectInputStream(bis);
        return  ois.readObject();
    }

}

在Husband类中存在clone和deepClone方法。现在对这两个方法进行测试。

package com.dhb.CloneTest;

import java.io.IOException;

public class CloneTest {

    public static void main(String[] args) {

        try {
            Husband husband = new Husband();
            System.out.println("husband birthday is :"+husband.getBirthday());
            System.out.println("wife birthday is :"+husband.getWife().getBirthday());
            System.out.println("***********************************************");
            Husband husband1 = (Husband) husband.clone();
            System.out.println("husband1 birthday is :"+husband1.getBirthday());
            System.out.println("wife birthday is :"+husband1.getWife().getBirthday());
            System.out.println("***********************************************");
            System.out.println("husband 是否相同："+(husband == husband1));
            System.out.println("wife 是否相同："+(husband.getWife() == husband1.getWife()));

            System.out.println("***********************************************");
            Husband husband2 = (Husband) husband.deepClone();
            System.out.println("husband2 birthday is :"+husband2.getBirthday());
            System.out.println("wife birthday is :"+husband2.getWife().getBirthday());
            System.out.println("***********************************************");
            System.out.println("husband 是否相同："+(husband == husband2));
            System.out.println("wife 是否相同："+(husband.getWife() == husband2.getWife()));

        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }

    }

}

运行结果：

husband birthday is :Mon Aug 07 19:03:38 CST 2017
wife birthday is :Mon Aug 07 19:03:38 CST 2017
***********************************************
husband1 birthday is :Mon Aug 07 19:03:38 CST 2017
wife birthday is :Mon Aug 07 19:03:38 CST 2017
***********************************************
husband 是否相同：false
wife 是否相同：true
***********************************************
husband2 birthday is :Mon Aug 07 19:03:38 CST 2017
wife birthday is :Mon Aug 07 19:03:38 CST 2017
***********************************************
husband 是否相同：false
wife 是否相同：false

注：上述代码中的@Data 是lombak的一个注解。

当然，实现深克隆的方法并不局限于流这一种办法，还可以通过json等其他办法实现。