java基礎入門-對象的淺複製與深複製

標籤：淺複製   深複製   對象   java   object   

這裡面涉及到兩個類，一個是person類，一個是測試類別test

首先我們說到的是淺複製，對某個對象實施Clone時對其是一無所知的，它僅僅是簡單地執行域對域的copy，如果是基礎資料型別 (Elementary Data Type)（int，float，char等）到沒什麼問題，基本遇上如string，Integer等不可變對象的時候也沒有什麼問題，但是如果遇上了date這個可變對象，或者是自己定義的可變對象，他只是簡單的複製一下引用這些可變對象，而不是把這些可變對象再一次的複製

先上person類，這裡面雖然是實現Cloneable介面，但是裡面沒有重寫方法，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;}@Overrideprotected Object clone() {Object obj = null;try {obj = super.clone();} catch (CloneNotSupportedException e) {// TODO Auto-generated catch blocke.printStackTrace();}return obj;}}

再上測試類別

package com.ray.object;import java.util.Date;/** * 淺複製和深複製 *  * @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 blocke.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());}}

輸出：

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

由上面可以看見，基本jack這個對象是clone了bill這個對象，但是這裡面只是簡單複製一下引用，當我們修改jack對象裡面的生日時，bill的生日竟然也跟著變了

下面，我們再說一下深複製，就是把對象的所有域全部複製一份

先上Person類，這次Person類重寫了clone方法，除了super之外，還把裡面的birthday屬性也複製一份

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;}@Overrideprotected Object clone() {Object obj = null;try {obj = super.clone();                        //下面把生日也複製一份Person person = (Person) obj;person.birthday = (Date) birthday.clone();} catch (CloneNotSupportedException e) {// TODO Auto-generated catch blocke.printStackTrace();}return obj;}}

再上Test類，其實Test類沒有做任何的改動，這裡只是為了閱讀方便，也寫上了

package com.ray.object;import java.util.Date;/** * 淺複製和深複製 *  * @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 blocke.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());}}

輸出：

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

由上面的輸出可以看到，jack裡面birthday的改動不再影響bill裡面的birthday

最後，我們來說一下使用=來copy對象，其實只是把對象的引用複製一份過去給另外的對象，對象是沒有做出任何改變

java基礎入門-對象的淺複製與深複製