Cloneable和clone的使用，以及深复制与浅复制的区别

一.Cloneable 的用途
  Cloneable和Serializable一样都是标记型接口，它们内部都没有方法和属性，implements Cloneable表示该对象能被克隆，能使用Object.clone()方法。如果没有implements Cloneable的类调用Object.clone()方法就会抛出CloneNotSupportedException。

二.克隆的分类
  (1)浅克隆（shallow clone），浅拷贝是指拷贝对象时仅仅拷贝对象本身和对象中的基本变量，而不拷贝对象包含的引用指向的对象。
  (2)深克隆（deep clone），深拷贝不仅拷贝对象本身，而且拷贝对象包含的引用指向的所有对象。

举例区别一下：对象A1中包含对B1的引用，B1中包含对C1的引用。浅拷贝A1得到A2，A2中依然包含对B1的引用，B1中依然包含对C1的引用。深拷贝则是对浅拷贝的递归，深拷贝A1得到A2，A2中包含对B2（B1的copy）的引用，B2中包含对C2（C1的copy）的引用。

三.克隆的举例
  要让一个对象进行克隆，其实就是两个步骤：
  1. 让该类实现java.lang.Cloneable接口；

  2. 重写（override）Object类的clone()方法。

public class Wife implements Cloneable {private int id;private String name;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 Wife(int id,String name) {this.id = id;this.name = name;}@Overridepublic int hashCode() {//myeclipse自动生成的final int prime = 31;int result = 1;result = prime * result + id;result = prime * result + ((name == null) ? 0 : name.hashCode());return result;}@Overridepublic boolean equals(Object obj) {//myeclipse自动生成的if (this == obj)return true;if (obj == null)return false;if (getClass() != obj.getClass())return false;Wife other = (Wife) obj;if (id != other.id)return false;if (name == null) {if (other.name != null)return false;} else if (!name.equals(other.name))return false;return true;}@Overridepublic Object clone() throws CloneNotSupportedException {return super.clone();}/** * @param args * @throws CloneNotSupportedException  */public static void main(String[] args) throws CloneNotSupportedException {Wife wife = new Wife(1,"wang");Wife wife2 = null;wife2 = (Wife) wife.clone();System.out.println("class same="+(wife.getClass()==wife2.getClass()));//trueSystem.out.println("object same="+(wife==wife2));//falseSystem.out.println("object equals="+(wife.equals(wife2)));//true}}

四.浅克隆的举例

public class Husband implements Cloneable {private int id;private Wife wife;public Wife getWife() {return wife;}public void setWife(Wife wife) {this.wife = wife;}public int getId() {return id;}public void setId(int id) {this.id = id;}public Husband(int id) {this.id = id;}@Overridepublic int hashCode() {//myeclipse自动生成的final int prime = 31;int result = 1;result = prime * result + id;return result;}@Overrideprotected Object clone() throws CloneNotSupportedException {return super.clone();}@Overridepublic boolean equals(Object obj) {//myeclipse自动生成的if (this == obj)return true;if (obj == null)return false;if (getClass() != obj.getClass())return false;Husband other = (Husband) obj;if (id != other.id)return false;return true;}/** * @param args * @throws CloneNotSupportedException  */public static void main(String[] args) throws CloneNotSupportedException {Wife wife = new Wife(1,"jin");Husband husband = new Husband(1);Husband husband2 = null;husband.setWife(wife);husband2 = (Husband) husband.clone();System.out.println("husband class same="+(husband.getClass()==husband2.getClass()));//trueSystem.out.println("husband object same="+(husband==husband2));//falseSystem.out.println("husband object equals="+(husband2.equals(husband)));//trueSystem.out.println("wife class same="+(husband.getWife().getClass()==husband2.getWife().getClass()));//trueSystem.out.println("wife object same="+(husband.getWife()==husband2.getWife()));//trueSystem.out.println("wife object equals="+(husband.getWife().equals(husband.getWife())));//true}}

五.深克隆的举例
  如果要深克隆，需要重写（override）Object类的clone()方法，并且在方法内部调用持有对象的clone()方法；注意如下代码的clone()方法

public class Husband implements Cloneable {private int id;private Wife wife;public Wife getWife() {return wife;}public void setWife(Wife wife) {this.wife = wife;}public int getId() {return id;}public void setId(int id) {this.id = id;}public Husband(int id) {this.id = id;}@Overridepublic int hashCode() {//myeclipse自动生成的final int prime = 31;int result = 1;result = prime * result + id;return result;}@Overrideprotected Object clone() throws CloneNotSupportedException {Husband husband = (Husband) super.clone();husband.wife = (Wife) husband.getWife().clone();return husband;}@Overridepublic boolean equals(Object obj) {//myeclipse自动生成的if (this == obj)return true;if (obj == null)return false;if (getClass() != obj.getClass())return false;Husband other = (Husband) obj;if (id != other.id)return false;return true;}/** * @param args * @throws CloneNotSupportedException  */public static void main(String[] args) throws CloneNotSupportedException {Wife wife = new Wife(1,"jin");Husband husband = new Husband(1);Husband husband2 = null;husband.setWife(wife);husband2 = (Husband) husband.clone();System.out.println("husband class same="+(husband.getClass()==husband2.getClass()));//trueSystem.out.println("husband object same="+(husband==husband2));//falseSystem.out.println("husband object equals="+(husband.equals(husband)));//trueSystem.out.println("wife class same="+(husband.getWife().getClass()==husband2.getWife().getClass()));//trueSystem.out.println("wife object same="+(husband.getWife()==husband2.getWife()));//falseSystem.out.println("wife object equals="+(husband.getWife().equals(husband.getWife())));//true}}

但是也有不足之处，如果Husband内有N个对象属性，突然改变了类的结构，还要重新修改clone()方法。解决办法：可以使用Serializable运用反序列化手段，调用java.io.ObjectInputStream对象的 readObject()方法。