原文地址：http://blog.csdn.net/kenthong/article/details/5758884
Part I
没啥好说的，直接开始Part II吧。
Part II
谈到了对象的克隆，就不得不说为什么要对对象进行克隆。Java中所有的对象都是保存在堆中，而堆是供全局共享的。也就是说，如果同一个Java程序的不同方法，只要能拿到某个对象的引用，引用者就可以随意的修改对象的内部数据（前提是这个对象的内部数据通过get/set方法曝露出来）。有的时候，我们编写的代码想让调用者只获得该对象的一个拷贝（也就是一个内容完全相同的对象，但是在内存中存在两个这样的对象），有什么办法可以做到呢？当然是克隆咯。
Part III
首先，我们是程序员，当然是用我们程序员的语言来交流。
import java.util.Date;
public class User implements Cloneable {
private String username;
private String password;
private Date birthdate;
public User(String username, String password, Date birthdate) {
this.username = username;
this.password = password;
this.birthdate = birthdate;
}
@Override
protected Object clone() throws CloneNotSupportedException {
return super.clone();
}
@Override
public int hashCode() {
// 省略equals的实现(可用eclipse自动生成)
}
@Override
public boolean equals(Object obj) {
// 省略equals的实现(可用eclipse自动生成)
}
// 省略一大堆get/set方法
}
上述代码构建了一个User类，并且实现了java.lang.Cloneable接口。顾名思义，Cloneable的意思就是说明这个类可以被克隆的意思。
而我们先去看看java.lang.Cloneable这个接口有些什么。
/*
* @(#)Cloneable.java 1.17 05/11/17
*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.lang;
/**
* A class implements the Cloneable interface to
* indicate to the {@link java.lang.Object#clone()} method that it
* is legal for that method to make a
* field-for-field copy of instances of that class.
*
* Invoking Object's clone method on an instance that does not implement the
* Cloneable interface results in the exception
* CloneNotSupportedException being thrown.
*
* By convention, classes that implement this interface should override
* Object.clone (which is protected) with a public method.
* See {@link java.lang.Object#clone()} for details on overriding this
* method.
*
* Note that this interface does not contain the clone method.
* Therefore, it is not possible to clone an object merely by virtue of the
* fact that it implements this interface. Even if the clone method is invoked
* reflectively, there is no guarantee that it will succeed.
*
* @author unascribed
* @version 1.17, 11/17/05
* @see java.lang.CloneNotSupportedException
* @see java.lang.Object#clone()
* @since JDK1.0
*/
public interface Cloneable {
}
不要惊讶，没错，除了一大堆的鸡肠以外，这个接口没有定义任何的方法签名。也就是说，我们要克隆一个对象，但是他又不给我提供一个方法。那该怎么办呢？不怕，我们还有全能的Object类，别忘记他可是所有类的始祖啊（神一般的存在着），所以，有事没事都该去问候一下他老人家。
/*
* @(#)Object.java 1.73 06/03/30
*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.lang;
/**
* Class Object is the root of the class hierarchy.
* Every class has Object as a superclass. All objects,
* including arrays, implement the methods of this class.
*
* @author unascribed
* @version 1.73, 03/30/06
* @see java.lang.Class
* @since JDK1.0
*/
public class Object {
// 省略N多的代码
/**
* Creates and returns a copy of this object. The precise meaning
* of "copy" may depend on the class of the object. The general
* intent is that, for any object x, the expression:
*
*
* x.clone() != x
* will be true, and that the expression:
*
*
* x.clone().getClass() == x.getClass()
* will be true, but these are not absolute requirements.
* While it is typically the ca