java基础入门-对象的浅克隆与深克隆

这里面涉及到两个类，一个是person类，一个是测试类test

首先我们说到的是浅克隆，对某个对象实施Clone时对其是一无所知的，它仅仅是简单地执行域对域的copy，如果是基本数据类型（int，float，char等）到没什么问题，基本遇上如string，Integer等不可变对象的时候也没有什么问题，但是如果遇上了date这个可变对象，或者是自己定义的可变对象，他只是简单的复制一下引用这些可变对象，而不是把这些可变对象再一次的复制

先上person类，这里面虽然是实现Cloneable接口，但是里面没有重写方法，只是super了一下就算了

package com.ray.object;

import java.util.Date;

/**
* 人
*
* @author ray
* @since 2015-05-07
* @version 1.0
*
*/
public class Person implements Cloneable {

private int id = 0;
private String name = "";
private Date birthday = null;

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

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

public Date getBirthday() {
return birthday;
}

public void setBirthday(Date birthday) {
this.birthday = birthday;
}

@Override
protected Object clone() {
Object obj = null;
try {
obj = super.clone();
} catch (CloneNotSupportedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return obj;
}

}

再上测试类

package com.ray.object;

import java.util.Date;

/**
* 浅克隆和深克隆
*
* @author ray
* @since 2015-05-07
* @version 1.0
*
*/
public class Test {

public static void main(String[] args) {
Person bill = new Person();
bill.setId(1);
bill.setName("bill");
bill.setBirthday(new Date());
System.out.println("bill.getId() --- "+bill.getId());
System.out.println("bill.getName() --- "+bill.getName());
System.out.println("bill.getBirthday() --- "+bill.getBirthday());
Person jack = (Person) bill.clone();
System.out.println("jack.getId() --- "+jack.getId());
System.out.println("jack.getName() --- "+jack.getName());
System.out.println("jack.getBirthday() --- "+jack.getBirthday());
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Date jacksBirthday = jack.getBirthday();
jacksBirthday.setTime(System.currentTimeMillis());
System.out.println("bill.getId() --- "+bill.getId());
System.out.println("bill.getName() --- "+bill.getName());
System.out.println("bill.getBirthday() --- "+bill.getBirthday());
System.out.println("jack.getId() --- "+jack.getId());
System.out.println("jack.getName() --- "+jack.getName());
System.out.println("jack.getBirthday() --- "+jack.getBirthday());
}
}

输出：
bill.getId() --- 1
bill.getName() --- bill
bill.getBirthday() --- Thu May 07 08:56:33 CST 2015
jack.getId() --- 1
jack.getName() --- bill
jack.getBirthday() --- Thu May 07 08:56:33 CST 2015
bill.getId() --- 1
bill.getName() --- bill
bill.getBirthday() --- Thu May 07 08:56:35 CST 2015
jack.getId() --- 1
jack.getName() --- bill
jack.getBirthday() --- Thu May 07 08:56:35 CST 2015



由上面可以看见，基本jack这个对象是clone了bill这个对象，但是这里面只是简单复制一下引用，当我们修改jack对象里面的生日时，bill的生日竟然也跟着变了

下面，我们再说一下深克隆，就是把对象的所有域全部复制一份

先上Person类，这次Person类重写了clone方法，除了super之外，还把里面的birthday属性也复制一份

package com.ray.object;

import java.util.Date;

/**
* 人
*
* @author ray
* @since 2015-05-07
* @version 1.0
*
*/
public class Person implements Cloneable {

private int id = 0;
private String name = "";
private Date birthday = null;

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

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

public Date getBirthday() {
return birthday;
}

public void setBirthday(Date birthday) {
this.birthday = birthday;
}

@Override
protected Object clone() {
Object obj = null;
try {
obj = super.clone();
//下面把生日也复制一份
Person person = (Person) obj;
person.birthday = (Date) birthday.clone();
} catch (CloneNotSupportedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return obj;
}

}

再上Test类，其实Test类没有做任何的改动，这里只是为了阅读方便，也写上了

package com.ray.object;

import java.util.Date;

/**
* 浅克隆和深克隆
*
* @author ray
* @since 2015-05-07
* @version 1.0
*
*/
public class Test {

public static void main(String[] args) {
Person bill = new Person();
bill.setId(1);
bill.setName("bill");
bill.setBirthday(new Date());
System.out.println("bill.getId() --- "+bill.getId());
System.out.println("bill.getName() --- "+bill.getName());
System.out.println("bill.getBirthday() --- "+bill.getBirthday());
Person jack = (Person) bill.clone();
System.out.println("jack.getId() --- "+jack.getId());
System.out.println("jack.getName() --- "+jack.getName());
System.out.println("jack.getBirthday() --- "+jack.getBirthday());
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Date jacksBirthday = jack.getBirthday();
jacksBirthday.setTime(System.currentTimeMillis());
System.out.println("bill.getId() --- "+bill.getId());
System.out.println("bill.getName() --- "+bill.getName());
System.out.println("bill.getBirthday() --- "+bill.getBirthday());
System.out.println("jack.getId() --- "+jack.getId());
System.out.println("jack.getName() --- "+jack.getName());
System.out.println("jack.getBirthday() --- "+jack.getBirthday());
}
}

输出：
bill.getId() --- 1
bill.getName() --- bill
bill.getBirthday() --- Thu May 07 09:22:03 CST 2015
jack.getId() --- 1
jack.getName() --- bill
jack.getBirthday() --- Thu May 07 09:22:03 CST 2015
bill.getId() --- 1
bill.getName() --- bill
bill.getBirthday() --- Thu May 07 09:22:03 CST 2015
jack.getId() --- 1
jack.getName() --- bill
jack.getBirthday() --- Thu May 07 09:22:05 CST 2015



由上面的输出可以看到，jack里面birthday的改动不再影响bill里面的birthday



最后，我们来说一下使用=来copy对象，其实只是把对象的引用复制一份过去给另外的对象，对象是没有做出任何改变

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