Java Object 对象拷贝

Java Object 对象拷贝

@author ixenos

 

 

 

JAVA 对象拷贝

---

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

---

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