JAVA 對象拷貝

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： 

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：

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 。

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

原文：http://blog.csdn.net/jdluojing/article/details/6963112