java clone

以下文章摘自：http://ttitfly.iteye.com/blog/155422

1.java里的clone分为：
A:浅复制（浅克隆）: 浅复制仅仅复制所考虑的对象，而不复制它所引用的对象。
b:深复制（深克隆）：深复制把要复制的对象所引用的对象都复制了一遍。
Java中对象的克隆,为了获取对象的一份拷贝，我们可以利用Object类的clone()方法。必须要遵循下面三点
1.在派生类中覆盖基类的clone()方法，并声明为public【Object类中的clone()方法为protected的】。
2.在派生类的clone()方法中，调用super.clone()。
3.在派生类中实现Cloneable接口。

Object类里的clone方法是浅复制（浅克隆）

浅复制（浅克隆）的例子如下：

package com.test;   
  
//浅复制（浅克隆）: 浅复制仅仅复制所考虑的对象，而不复制它所引用的对象。   
//深复制（深克隆）：深复制把要复制的对象所引用的对象都复制了一遍。   
//   
//Java中对象的克隆,为了获取对象的一份拷贝，我们可以利用Object类的clone()方法。必须要遵循下面三点   
//1.在派生类中覆盖基类的clone()方法，并声明为public【Object类中的clone()方法为protected的】。   
//2.在派生类的clone()方法中，调用super.clone()。   
//3.在派生类中实现Cloneable接口。   
  
//[color=red]Object类里的clone方法是浅复制（浅克隆）[/color]public class CloneTest {   
  
    public static void main(String[] args) throws Exception{   
        //teacher对象将被clone出来的Student对象共享.   
        Teacher teacher = new Teacher();   
        teacher.setAge(40);   
        teacher.setName("Teacher zhang");   
           
        Student student1 = new Student();   
        student1.setAge(20);   
        student1.setName("zhangsan");   
        student1.setTeacher(teacher);   
           
        //复制出来一个对象student2   
        Student student2 = (Student)student1.clone();   
        System.out.println(student2.getAge());   
        System.out.println(student2.getName());   
           
           
        System.out.println("~~~~~~~~~~~~~~~~~~~~~~");   
        System.out.println(student1.getTeacher().getAge());   
        System.out.println(student1.getTeacher().getName());   
           
           
        //修改student2的引用对象   
        student2.getTeacher().setAge(50);   
        student2.getTeacher().setName("Teacher Li");   
           
        System.out.println("~~~~~~~~~~~~~~~~~~~~~~");   
        System.out.println(student1.getTeacher().getAge());   
        System.out.println(student1.getTeacher().getName());   
    }   
}   
  
class Teacher {   
    public int age;   
    public String name;   
       
    public int getAge() {   
        return age;   
    }   
    public void setAge(int age) {   
        this.age = age;   
    }   
    public String getName() {   
        return name;   
    }   
    public void setName(String name) {   
        this.name = name;   
    }   
       
       
}   
  
class Student implements Cloneable{   
       
    public int age ;   
    public String name;   
    public Teacher teacher;   
    public int getAge() {   
        return age;   
    }   
    public void setAge(int age) {   
        this.age = age;   
    }   
    public String getName() {   
        return name;   
    }   
    public void setName(String name) {   
        this.name = name;   
    }   
    public Teacher getTeacher() {   
        return teacher;   
    }   
    public void setTeacher(Teacher teacher) {   
        this.teacher = teacher;   
    }   
    @Override  
    public Object clone() throws CloneNotSupportedException {   
        return super.clone();   
    }   
       
       
}   
输出结果为：   
20  
zhangsan   
~~~~~~~~~~~~~~~~~~~~~~   
40  
Teacher zhang   
~~~~~~~~~~~~~~~~~~~~~~   
50  
Teacher Li  

2.深复制（深Clone）例子：

package com.test1;   
  
//深clone   
public class DeepCloneTest {   
  
    public static void main(String[] args) throws Exception{   
        //teacher对象将不被clone出来的Student对象共享.   
        Teacher teacher = new Teacher();   
        teacher.setAge(40);   
        teacher.setName("Teacher zhang");   
           
        Student student1 = new Student();   
        student1.setAge(20);   
        student1.setName("zhangsan");   
        student1.setTeacher(teacher);   
           
        //复制出来一个对象student2   
        Student student2 = (Student)student1.clone();   
        System.out.println(student2.getAge());   
        System.out.println(student2.getName());   
           
           
        System.out.println("~~~~~~~~~~~~~~~~~~~~~~");   
        System.out.println(student1.getTeacher().getAge());   
        System.out.println(student1.getTeacher().getName());   
           
           
        //修改student2的引用对象   
        student2.getTeacher().setAge(50);   
        student2.getTeacher().setName("Teacher Li");   
           
        System.out.println("~~~~~~~~~~~~~~~~~~~~~~");   
        System.out.println(student1.getTeacher().getAge());   
        System.out.println(student1.getTeacher().getName());   
    }   
}   
  
class Teacher implements Cloneable{   
    public int age;   
    public String name;   
       
    public int getAge() {   
        return age;   
    }   
    public void setAge(int age) {   
        this.age = age;   
    }   
    public String getName() {   
        return name;   
    }   
    public void setName(String name) {   
        this.name = name;   
    }   
    @Override  
    public Object clone() throws CloneNotSupportedException {   
        return super.clone();   
    }   
       
}   
  
class Student implements Cloneable{   
       
    public int age ;   
    public String name;   
    public Teacher teacher;   
    public int getAge() {   
        return age;   
    }   
    public void setAge(int age) {   
        this.age = age;   
    }   
    public String getName() {   
        return name;   
    }   
    public void setName(String name) {   
        this.name = name;   
    }   
    public Teacher getTeacher() {   
        return teacher;   
    }   
    public void setTeacher(Teacher teacher) {   
        this.teacher = teacher;   
    }   
    @Override  
    public Object clone() throws CloneNotSupportedException {   
        Student student = (Student)super.clone();   
        //将引用的对象teacher也clone下   
        student.setTeacher((Teacher)(student.getTeacher().clone()));   
        return student;   
    }   
       
       
}   
输出结果为：   
20  
zhangsan   
~~~~~~~~~~~~~~~~~~~~~~   
40  
Teacher zhang   
~~~~~~~~~~~~~~~~~~~~~~   
40  
Teacher zhang  

3.利用序列化来做深复制,把对象写到流里的过程是序列化（Serilization）过程，而把对象从流中读出来的过程则叫做反序列化（Deserialization）过程。应当指出的是，写在流里的是对象的一个拷贝，而原对象仍然存在于JVM里面。，利用这个特性，可以做深拷贝

package com.test3;   
  
import java.io.ByteArrayInputStream;   
import java.io.ByteArrayOutputStream;   
import java.io.ObjectInputStream;   
import java.io.ObjectOutputStream;   
import java.io.Serializable;   
//利用序列化来做深复制   
//深clone   
public class DeepCloneTest {   
  
    public static void main(String[] args) throws Exception{   
        //teacher对象将不被clone出来的Student对象共享.   
        Teacher teacher = new Teacher();   
        teacher.setAge(40);   
        teacher.setName("Teacher zhang");   
           
        Student student1 = new Student();   
        student1.setAge(20);   
        student1.setName("zhangsan");   
        student1.setTeacher(teacher);   
           
        //复制出来一个对象student2   
        Student student2 = (Student)student1.deepCopy();   
        System.out.println(student2.getAge());   
        System.out.println(student2.getName());   
           
           
        System.out.println("~~~~~~~~~~~~~~~~~~~~~~");   
        System.out.println(student1.getTeacher().getAge());   
        System.out.println(student1.getTeacher().getName());   
           
           
        //修改student2的引用对象   
        student2.getTeacher().setAge(50);   
        student2.getTeacher().setName("Teacher Li");   
           
        System.out.println("~~~~~~~~~~~~~~~~~~~~~~");   
        System.out.println(student1.getTeacher().getAge());   
        System.out.println(student1.getTeacher().getName());   
    }   
}   
  
class Teacher implements Serializable{   
       
    private static final long serialVersionUID = -8834559347461591191L;   
       
    public int age;   
    public String name;   
       
    public int getAge() {   
        return age;   
    }   
    public void setAge(int age) {   
        this.age = age;   
    }   
    public String getName() {   
        return name;   
    }   
    public void setName(String name) {   
        this.name = name;   
    }   
       
}   
  
class Student implements Serializable{   
       
    //serialVersionUID 如果你的对象序列化后存到硬盘上面后，可是后来你却更改了类的field(增加或减少或改名)，当你反序列化时，就会出现Exception的，这样就会造成不兼容性的问题。    
    //但当serialVersionUID相同时，它就会将不一样的field以type的缺省值赋值(如int型的是0,String型的是null等)，这个可以避开不兼容性的问题。所以最好给serialVersionUID赋值   
    private static final long serialVersionUID = 7991552226614088458L;   
       
    public int age ;   
    public String name;   
    public Teacher teacher;   
    public int getAge() {   
        return age;   
    }   
    public void setAge(int age) {   
        this.age = age;   
    }   
    public String getName() {   
        return name;   
    }   
    public void setName(String name) {   
        this.name = name;   
    }   
    public Teacher getTeacher() {   
        return teacher;   
    }   
    public void setTeacher(Teacher teacher) {   
        this.teacher = teacher;   
    }   
       
    public Object deepCopy() throws Exception{   
        //将该对象序列化成流,因为写在流里的是对象的一个拷贝，而原对象仍然存在于JVM里面。所以利用这个特性可以实现对象的深拷贝   
        ByteArrayOutputStream bos = new ByteArrayOutputStream();   
  
        ObjectOutputStream oos = new ObjectOutputStream(bos);   
  
        oos.writeObject(this);   
  
        //将流序列化成对象   
        ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());   
  
        ObjectInputStream ois = new ObjectInputStream(bis);   
  
        return ois.readObject();   
    }   
       
       
}   
输出结果为：   
20  
zhangsan   
~~~~~~~~~~~~~~~~~~~~~~   
40  
Teacher zhang   
~~~~~~~~~~~~~~~~~~~~~~   
40  
Teacher zhang