java 浅复制和深复制

原文：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student2Student 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;}@Overridepublic Object clone() throws CloneNotSupportedException {return super.clone();}}输出结果为：20zhangsan~~~~~~~~~~~~~~~~~~~~~~40Teacher zhang~~~~~~~~~~~~~~~~~~~~~~50Teacher Li

2.深复制（深Clone）例子： 

package com.test1;//深clonepublic 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student2Student 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;}@Overridepublic 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;}@Overridepublic 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：20zhangsan~~~~~~~~~~~~~~~~~~~~~~40Teacher zhang~~~~~~~~~~~~~~~~~~~~~~40Teacher 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clonepublic 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student2Student 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：20zhangsan~~~~~~~~~~~~~~~~~~~~~~40Teacher zhang~~~~~~~~~~~~~~~~~~~~~~40Teacher zhang