Java Object 对象拷贝

Java Object 对象拷贝

@author ixenos

JAVA 对象拷贝

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Java里的clone分为： 　　

　　1.浅拷贝：浅复制仅仅复制所考虑的对象，而不复制它所引用的对象，Object类里的clone方法是浅拷贝 　　

　　2.深拷贝：深复制把要复制的对象及其所引用的对象都复制了一遍

　　3.序列化深拷贝：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

深拷贝时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

示例

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浅拷贝的例子：

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  

深拷贝例子：

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()));          // student.getTeacher().clone()
        return student;
    }
}  

输出结果为：
20
zhangsan
~~~~~~~~~~~~~~~~~~~~~~
40
Teacher zhang
~~~~~~~~~~~~~~~~~~~~~~
40
Teacher zhang  

序列化深拷贝例子：

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;
    }
    /**
     *    因为对象序列化会自然地对对象深拷贝，再利用“序列化-反序列化”读出
     */
    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);
      //this很关键，引用当前对象，当然，这是值传递
        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