JAVA 对象拷贝

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： 

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：

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 。

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