Cloneable 和 clone()的总结和使用

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;
	}

	@Override
	public 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;
	}

	@Override
	public 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;
	}

	@Override
	public 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()));//true
		System.out.println("object same="+(wife==wife2));//false
		System.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;
	}

	@Override
	public int hashCode() {//myeclipse自动生成的
		final int prime = 31;
		int result = 1;
		result = prime * result + id;
		return result;
	}

	@Override
	protected Object clone() throws CloneNotSupportedException {
		return super.clone();
	}

	@Override
	public 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()));//true
		System.out.println("husband object same="+(husband==husband2));//false
		System.out.println("husband object equals="+(husband.equals(husband)));//true
		System.out.println("wife class same="+(husband.getWife().getClass()==husband2.getWife().getClass()));//true
		System.out.println("wife object same="+(husband.getWife()==husband2.getWife()));//true
		System.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;
	}

	@Override
	public int hashCode() {//myeclipse自动生成的
		final int prime = 31;
		int result = 1;
		result = prime * result + id;
		return result;
	}

	@Override
	protected Object clone() throws CloneNotSupportedException {
		Husband husband = (Husband) super.clone();
		husband.wife = (Wife) husband.getWife().clone();
		return husband;
	}

	@Override
	public 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()));//true
		System.out.println("husband object same="+(husband==husband2));//false
		System.out.println("husband object equals="+(husband.equals(husband)));//true
		System.out.println("wife class same="+(husband.getWife().getClass()==husband2.getWife().getClass()));//true
		System.out.println("wife object same="+(husband.getWife()==husband2.getWife()));//false
		System.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。

参考java创建对象的第四种方法：
http://ncs123.iteye.com/blog/1775661