java clone

 1.java裏的clone分爲：
A:淺複製（淺克隆）: 淺複製僅僅複製所考慮的對象，而不復制它所引用的對象。
b:深複製（深克隆）：深複製把要複製的對象所引用的對象都複製了一遍。
Java中對象的克隆,爲了獲取對象的一份拷貝，我們可以利用Object類的clone()方法。必須要遵循下面三點
1.在派生類中覆蓋基類的clone()方法，並聲明爲public【Object類中的clone()方法爲protected的】。
2.在派生類的clone()方法中，調用super.clone()。
3.在派生類中實現Cloneable接口。

Object類裏的clone方法是淺複製（淺克隆）

淺複製（淺克隆）的例子如下：

package com.test;   
  
//淺複製（淺克隆）: 淺複製僅僅複製所考慮的對象，而不復制它所引用的對象。   
//深複製（深克隆）：深複製把要複製的對象所引用的對象都複製了一遍。   
//   
//Java中對象的克隆,爲了獲取對象的一份拷貝，我們可以利用Object類的clone()方法。必須要遵循下面三點   
//1.在派生類中覆蓋基類的clone()方法，並聲明爲public【Object類中的clone()方法爲protected的】。   
//2.在派生類的clone()方法中，調用super.clone()。   
//3.在派生類中實現Cloneable接口。   
  
//[color=red]Object類裏的clone方法是淺複製（淺克隆）[/color]

public class CloneTest {   
  
    public static void main(String[] args) throws Exception{   
        //teacher對象將被clone出來的Student對象共享.   
        Teacher teacher = new Teacher();   
        teacher.setAge(40);   
        teacher.setName("Teacher zhang");   
           
        Student student1 = new Student();   
        student1.setAge(20);   
        student1.setName("zhangsan");   
        student1.setTeacher(teacher);   
           
        //複製出來一個對象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的引用對象   
        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();   
    }   
       
       
}   

輸出結果爲：  
20 
zhangsan  
~~~~~~~~~~~~~~~~~~~~~~  
40 
Teacher zhang  
~~~~~~~~~~~~~~~~~~~~~~  
50 
Teacher Li 

 

2.深複製（深Clone）例子：

package com.test1;

//深clone
public class DeepCloneTest {

	public static void main(String[] args) throws Exception{
		//teacher對象將不被clone出來的Student對象共享.
		Teacher teacher = new Teacher();
		teacher.setAge(40);
		teacher.setName("Teacher zhang");
		
		Student student1 = new Student();
		student1.setAge(20);
		student1.setName("zhangsan");
		student1.setTeacher(teacher);
		
		//複製出來一個對象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的引用對象
		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();
		//將引用的對象teacher也clone下
		student.setTeacher((Teacher)(student.getTeacher().clone()));
		return student;
	}
	
	
}

輸出結果爲：
20
zhangsan
~~~~~~~~~~~~~~~~~~~~~~
40
Teacher zhang
~~~~~~~~~~~~~~~~~~~~~~
40
Teacher zhang

 

3.利用序列化來做深複製,把對象寫到流裏的過程是序列化（Serilization）過程，而把對象從流中讀出來的過程則叫做反序列化（Deserialization）過程。應當指出的是，寫在流裏的是對象的一個拷貝，而原對象仍然存在於JVM裏面。，利用這個特性，可以做深拷貝

package com.test3;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
//利用序列化來做深複製
//深clone
public class DeepCloneTest {

	public static void main(String[] args) throws Exception{
		//teacher對象將不被clone出來的Student對象共享.
		Teacher teacher = new Teacher();
		teacher.setAge(40);
		teacher.setName("Teacher zhang");
		
		Student student1 = new Student();
		student1.setAge(20);
		student1.setName("zhangsan");
		student1.setTeacher(teacher);
		
		//複製出來一個對象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的引用對象
		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 如果你的對象序列化後存到硬盤上面後，可是後來你卻更改了類的field(增加或減少或改名)，當你反序列化時，就會出現Exception的，這樣就會造成不兼容性的問題。 
	//但當serialVersionUID相同時，它就會將不一樣的field以type的缺省值賦值(如int型的是0,String型的是null等)，這個可以避開不兼容性的問題。所以最好給serialVersionUID賦值
	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{
		//將該對象序列化成流,因爲寫在流裏的是對象的一個拷貝，而原對象仍然存在於JVM裏面。所以利用這個特性可以實現對象的深拷貝
		ByteArrayOutputStream bos = new ByteArrayOutputStream();

		ObjectOutputStream oos = new ObjectOutputStream(bos);

		oos.writeObject(this);

		//將流序列化成對象
		ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());

		ObjectInputStream ois = new ObjectInputStream(bis);

		return ois.readObject();
	}
	
	
}

輸出結果爲：
20
zhangsan
~~~~~~~~~~~~~~~~~~~~~~
40
Teacher zhang
~~~~~~~~~~~~~~~~~~~~~~
40
Teacher zhang