正确增加Cloneable接口

今天调试程序，发现在解析的时候使用了clone函数，但是得到的结果是null，很奇怪。

看代码，override了clone函数，还是得到null。

继续搜索stackoverflow，发现没有增加Cloneable接口声明。

增加声明后，问题解决。

http://stackoverflow.com/questions/1052340/what-is-wrong-with-this-clone

The standard pattern for making a class cloneable is:

1. Implement Cloneable
2. Override the clone() method and make it public
3. In clone() call super.clone() and then copy any mutable object's state

You should not create a new object using new. The proper way is to callsuper.clone() for a new instance. Object's clone() is special and will create a new copy of the object and copy its primitive fields and references.

你不需要使用new关键字创建新对象。合适的方法是调用super.clone建立新对象。Object的clone()是特别的，会创建一个新的对象拷贝，以及拷贝它的基本类型和引用。(这里涉及到深拷贝和浅拷贝，请自行glgoo.com)

For example:

public class Person implements Cloneable {    protected String name;    // Note that overridden clone is public    public Object clone() {        Person clone = (Person)super.clone();        // No need to copy name as the reference will be        // copied by Object's clone and String is immutable        return clone;    }}public class Employee extends Person {    protected int id;    protected java.awt.Point location;    public Object clone() {        Employee  clone = (Employee )super.clone();        // No need to copy id as Object's clone has already copied it        // Need to clone location as Point is mutable and could change        clone.location = location.clone();        return clone;    }}