Java基础五：浅clone和深clone

一、概念

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，还有复制对象里面的引用，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.在派生类中实现Cloneable接口。

3.在派生类的重写clone()方法，调用super.clone()。

Object类里的clone方法是浅复制（浅克隆）

二、例子

1.浅克隆

类1：

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;    }}

类2：

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();    }}

主类：

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());    }}

输出结果为：

20zhangsan~~~~~~~~~~~~~~~~~~~~~~40Teacher zhang~~~~~~~~~~~~~~~~~~~~~~50Teacher Li

修改student2的teacher对象里面的age和name，发现student1的teacher的属性也发生改变，说明在clone的时候，只clone了student1中teacher对象的引用（存在栈中的），并没有clone teacher对象（存在堆中），所以student1和student2的teacher指向的是同一个对象。

2.深克隆

类1：

    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();    }}

类2：

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;    }}

主类：

//深clonepublic 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());    }}

输出结果为：

20zhangsan~~~~~~~~~~~~~~~~~~~~~~40Teacher zhang~~~~~~~~~~~~~~~~~~~~~~40Teacher zhang

三、利用序列化做深clone

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
类1：

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;    }}

类2：

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();    }}

主类：

//利用序列化来做深复制//深clonepublic 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());    }}

输出结果为：

20zhangsan~~~~~~~~~~~~~~~~~~~~~~40Teacher zhang~~~~~~~~~~~~~~~~~~~~~~40Teacher zhang