[Series] in java - deep and shallow clone clone

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　　Java support us to clone an object, typically used in decorative patterns and prototype mode. So what is a deep clone, what is a shallow clone it.

　　] [Shallow clone is usually only the instance cloned copy, but other sub-objects inside, are common.

　　[Deep] clone, clone when the reference is copied its sub-objects, which all variables and all child objects and an additional copy of a copy.

　　The following two examples can be very good description of their differences:

　　First, look at the class diagram

　　Husband wife class has one pair of reference, when the shallow clones, will refer to the same variable wife Wife; while deep clones, will point to different Wife. Below about verification:

　　[Shallow clone]

 1 public Object clone() {
 2         Husband husband = null;
 3         try{
 4             husband = (Husband)super.clone();
 5         }catch(CloneNotSupportedException e){
 6             e.printStackTrace();
 7         }finally{
 8             return husband;
 9         }
10     }

　　[Cloning] deeply

 1 public Object deepClone() throws IOException,ClassNotFoundException {
 2         //将对象写到流里
 3         ByteArrayOutputStream bos = new ByteArrayOutputStream();
 4         ObjectOutputStream oos = new ObjectOutputStream(bos);
 5         oos.writeObject(this);
 6         //从流里读回来
 7         ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
 8         ObjectInputStream ois = new ObjectInputStream(bis);
 9         return ois.readObject();
10     }

　　[All] Code

  1 package com.xingoo.clone;
  2 
  3 import java.io.ByteArrayInputStream;
  4 import java.io.ByteArrayOutputStream;
  5 import java.io.IOException;
  6 import java.io.ObjectInputStream;
  7 import java.io.ObjectOutputStream;
  8 import java.io.Serializable;
  9 import java.util.Date;
 10 
 11 class Wife implements Serializable{
 12     private String name;
 13     private Date birthday;
 14     
 15     public Wife(){
 16         name = "芙蓉姐姐";
 17         birthday = new Date();
 18     }
 19     public Date getBirthday(){
 20         return birthday;
 21     }
 22     
 23     public String getName() {
 24         return name;
 25     }
 26     public void setName(String name) {
 27         this.name = name;
 28     }
 29 }
 30 class Husband implements Cloneable,Serializable{
 31     private Wife wife;
 32     private Date birthday;
 33     
 34     public Husband(){
 35         wife = new Wife();
 36         birthday = new Date();
 37     }
 38     
 39     public Wife getWife(){
 40         return wife;
 41     }
 42     
 43     public Date getBirthday(){
 44         return birthday;
 45     }
 46     /**
 47      * 浅克隆一个对象
 48      */
 49     public Object clone() {
 50         Husband husband = null;
 51         try{
 52             husband = (Husband)super.clone();
 53         }catch(CloneNotSupportedException e){
 54             e.printStackTrace();
 55         }finally{
 56             return husband;
 57         }
 58     }
 59     /**
 60      * 利用串行化深克隆一个对象，把对象以及它的引用读到流里，在写入其他的对象
 61      * @return
 62      * @throws IOException
 63      * @throws ClassNotFoundException
 64      */
 65     public Object deepClone() throws IOException,ClassNotFoundException {
 66         //将对象写到流里
 67         ByteArrayOutputStream bos = new ByteArrayOutputStream();
 68         ObjectOutputStream oos = new ObjectOutputStream(bos);
 69         oos.writeObject(this);
 70         //从流里读回来
 71         ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
 72         ObjectInputStream ois = new ObjectInputStream(bis);
 73         return ois.readObject();
 74     }
 75 }
 76 public class Test {
 77     public static void main(String[] args){
 78         try{
 79             Husband husband = new Husband();
 80             System.out.println("husband birthday "+husband.getBirthday().getTime());
 81             System.out.println("wife birthday "+husband.getWife().getBirthday().getTime());
 82             System.out.println();
 83             Husband husband1 = (Husband)husband.clone();
 84             System.out.println("husband1 birthday "+husband1.getBirthday().getTime());
 85             System.out.println("wife birthday "+husband1.getWife().getBirthday().getTime());
 86             System.out.println();
 87             System.out.println("是否是同一个husband "+(husband == husband1));
 88             System.out.println("是否是同一个wife "+ (husband.getWife() == husband1.getWife()));
 89             System.out.println();
 90             Husband husband2 = (Husband)husband.deepClone();
 91             System.out.println("husband2 birthday "+husband2.getBirthday().getTime());
 92             System.out.println("wife birthday "+husband2.getWife().getBirthday().getTime());
 93             System.out.println();
 94             System.out.println("是否是同一个husband "+(husband == husband2));
 95             System.out.println("是否是同一个wife "+ (husband.getWife() == husband2.getWife()));
 96         }catch(Exception e){
 97             e.printStackTrace();
 98         }
 99     }
100 }

　　【operation result】

husband birthday 1414247244668
wife birthday 1414247244668

husband1 birthday 1414247244668
wife birthday 1414247244668
是否是同一个husband false
是否是同一个wife true

husband2 birthday 1414247244668
wife birthday 1414247244668
是否是同一个husband false
是否是同一个wife false

 

Reproduced in: https: //my.oschina.net/u/204616/blog/545277