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