Java中对象的复制/拷贝

在Java中对对象的复制分为2种：浅复制和深复制。

浅复制：仅复制目标对象的引用，共享同一内存对象。所以，对原对象的修改同样作用于复制的对象，反过来也一样。

深复制：相当于重新创建一个和原对象相同类型的对象，并复制原对象的属性方法等。

例1：浅复制

首先创建 User,java 类

package com.clonetest;public class User{private String username;private String password;public User() {}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}}

创建测试类 CloneTestSimple.java

package com.clonetest;public class CloneTestSimple {public static void main(String[] args) {// Create User and initializeUser user = new User();user.setUsername("Tom");user.setPassword("tom");// Clone User Object and output parametersUser cloneUser;cloneUser = user;System.out.println("================ New clone user ===============");System.out.println("Origin user: " + user.getUsername() + ", "+ user.getPassword());System.out.println("Clone user: " + cloneUser.getUsername() + ", "+ cloneUser.getPassword());// Update useruser.setUsername("Jerry");user.setPassword("Jerry");System.out.println("================ After update user ===============");System.out.println("Origin user: " + user.getUsername() + ", "+ user.getPassword());System.out.println("Clone user: " + cloneUser.getUsername() + ", "+ cloneUser.getPassword());// Update cloneUsercloneUser.setUsername("Tom an Jerry");cloneUser.setPassword("Tom and Jerry");System.out.println("================ After update clone user ===============");System.out.println("Origin user: " + user.getUsername() + ", "+ user.getPassword());System.out.println("Clone user: " + cloneUser.getUsername() + ", "+ cloneUser.getPassword());}}

测试结果如下：

================ New clone user ===============
Origin user: Tom, tom
Clone user: Tom, tom
================ After update user ===============
Origin user: Jerry, Jerry
Clone user: Jerry, Jerry
================ After update clone user ===============
Origin user: Tom an Jerry, Tom and Jerry
Clone user: Tom an Jerry, Tom and Jerry

例2：深复制

2.1 通过实现 Cloneable 接口，重写 clone 方法实现：

改写上例中的 User.java 类

package com.clonetest;public class User implements Cloneable{private String username;private String password;public User() {}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}@Overridepublic Object clone(){Object obj = null;try {obj = super.clone();} catch (CloneNotSupportedException e) {e.printStackTrace();}return obj;}}

改写测试类 CloneTestSimple.java ：

package com.clonetest;public class CloneTestSimple {public static void main(String[] args) {// Create User and initializeUser user = new User();user.setUsername("Tom");user.setPassword("tom");// Clone User Object and output parametersUser cloneUser;cloneUser = (User) user.clone();System.out.println("================ New clone user ===============");System.out.println("Origin user: " + user.getUsername() + ", "+ user.getPassword());System.out.println("Clone user: " + cloneUser.getUsername() + ", "+ cloneUser.getPassword());// Update useruser.setUsername("Jerry");user.setPassword("Jerry");System.out.println("================ After update user ===============");System.out.println("Origin user: " + user.getUsername() + ", "+ user.getPassword());System.out.println("Clone user: " + cloneUser.getUsername() + ", "+ cloneUser.getPassword());// Update cloneUsercloneUser.setUsername("Tom an Jerry");cloneUser.setPassword("Tom and Jerry");System.out.println("================ After update clone user ===============");System.out.println("Origin user: " + user.getUsername() + ", "+ user.getPassword());System.out.println("Clone user: " + cloneUser.getUsername() + ", "+ cloneUser.getPassword());}}

测试结果如下：
================ New clone user ===============
Origin user: Tom, tom
Clone user: Tom, tom
================ After update user ===============
Origin user: Jerry, Jerry
Clone user: Tom, tom
================ After update clone user ===============
Origin user: Jerry, Jerry
Clone user: Tom an Jerry, Tom and Jerry

2.2 通过实现 Serializable 接口，用序列化和反序列化实现：

创建测试类 Account.java

package com.clonetest;import java.io.Serializable;@SuppressWarnings("serial")public class Account implements Serializable {private String firstname;private String lastname;public Account(){}public String getFirstname() {return firstname;}public void setFirstname(String firstname) {this.firstname = firstname;}public String getLastname() {return lastname;}public void setLastname(String lastname) {this.lastname = lastname;}}

改写测试类 CloneTestSimple.java ：

package com.clonetest;import java.io.ByteArrayInputStream;import java.io.ByteArrayOutputStream;import java.io.IOException;import java.io.ObjectInputStream;import java.io.ObjectOutputStream;public class CloneTestSimple {public static void main(String[] args) {Account account = new Account();account.setFirstname("Sherlock");account.setLastname("Homles");try {ByteArrayOutputStream baos = new ByteArrayOutputStream();ObjectOutputStream oos = new ObjectOutputStream(baos);oos.writeObject(account);ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());ObjectInputStream ois = new ObjectInputStream(bais);Account cloneAccount = (Account) ois.readObject();System.out.println("================ New clone account ===============");System.out.println("Origin account: " + account.getFirstname() + ", "+ account.getLastname());System.out.println("Clone account: " + cloneAccount.getFirstname() + ", "+ cloneAccount.getLastname());account.setFirstname("William");account.setLastname("Shakespeare");System.out.println("================ update origin account ===============");System.out.println("Origin account: " + account.getFirstname() + ", "+ account.getLastname());System.out.println("Clone account: " + cloneAccount.getFirstname() + ", "+ cloneAccount.getLastname());cloneAccount.setFirstname("Will");cloneAccount.setLastname("Smith");System.out.println("================ update clone account ===============");System.out.println("Origin account: " + account.getFirstname() + ", "+ account.getLastname());System.out.println("Clone account: " + cloneAccount.getFirstname() + ", "+ cloneAccount.getLastname());} catch (IOException e) {e.printStackTrace();} catch (ClassNotFoundException e) {e.printStackTrace();}}}

测试结果如下：
================ New clone account ===============
Origin account: Sherlock, Homles
Clone account: Sherlock, Homles
================ update origin account ===============
Origin account: William, Shakespeare
Clone account: Sherlock, Homles
================ update clone account ===============
Origin account: William, Shakespeare
Clone account: Will, Smith