深克隆与浅克隆

作者: Lucksheep | 来源:发表于2020-06-16 15:46 被阅读0次

一、克隆的作用

快速构建一个和已有对象相同的副本，创建一个新对象，将已有对象的数据导入到新对象里面；

二、克隆基本简介

我们说的克隆，都是基于超类 Object 来的，里面有个native方法，具体实现是它调用底层C语言的实现，我们是看不到的

protected native Object clone() throws CloneNotSupportedException;

由此可知，有几个约束

使用时必须继承Object类，我们所有的类都是Object派生的
接收对象必须强转
必须实现 Cloneable 接口标识（表示重写了clone() ）

不实现这个接口会发生什么呢？

public class User{

    private String userName;

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    @Override
    protected Object clone() throws CloneNotSupportedException{
        return super.clone();
    }

    public static void main(String[] args) throws CloneNotSupportedException {
        User user=new User();
        user.setUserName("zhangsan");
        System.out.println(JSONObject.toJSONString(user));
        User user1= (User) user.clone();
        System.out.println(JSONObject.toJSONString(user1));
    }
}

结果：

{"userName":"zhangsan"}
Exception in thread "main" java.lang.CloneNotSupportedException: com.demo.cs.study.clones.User
    at java.lang.Object.clone(Native Method)
    at com.demo.cs.study.clones.User.clone(User.java:19)
    at com.demo.cs.study.clones.User.main(User.java:32)

添加实现后

public class User implements Cloneable{

    private String userName;

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    @Override
    protected Object clone() throws CloneNotSupportedException{
        return super.clone();
    }

    public static void main(String[] args) throws CloneNotSupportedException {
        User user=new User();
        user.setUserName("zhangsan");
        System.out.println(JSONObject.toJSONString(user));
        User user1= (User) user.clone();
        System.out.println(JSONObject.toJSONString(user1));
    }
}

结果：

{"userName":"zhangsan"}
{"userName":"zhangsan"}

1、浅克隆

概念：如果被复制的对象所有的变量与原来的变量值相同，且所持有对其它对象的引用任然指向原来的对象就叫浅克隆

User.java

public class User implements Cloneable{

    private String userName;

    private HavingDinner havingDinner;

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public HavingDinner getHavingDinner() {
        return havingDinner;
    }

    public void setHavingDinner(HavingDinner havingDinner) {
        this.havingDinner = havingDinner;
    }

    @Override
    protected Object clone() throws CloneNotSupportedException{
        return super.clone();
    }
}

HavingDinner.java

public class HavingDinner {

    private String foodName;

    public String getFoodName() {
        return foodName;
    }

    public void setFoodName(String foodName) {
        this.foodName = foodName;
    }

    public HavingDinner(String foodName) {
        this.foodName = foodName;
    }
}

Demo.java

public class Demo {
    public static void main(String[] args) throws CloneNotSupportedException {
        HavingDinner hd=new HavingDinner("青椒炒萝卜");
        User user=new User();
        user.setUserName("哈比");
        user.setHavingDinner(hd);
        User user1= (User) user.clone();
        user1.setUserName("哈比2");
        User user2= (User) user.clone();
        user2.setUserName("哈士奇");
        System.out.println(user.getUserName()+"-->今天晚上要吃"+user.getHavingDinner().getFoodName()+"  引用地址："+user.getHavingDinner());
        System.out.println(user1.getUserName()+"-->今天晚上要吃"+user1.getHavingDinner().getFoodName()+"  引用地址："+user1.getHavingDinner());
        System.out.println(user2.getUserName()+"-->今天晚上要吃"+user2.getHavingDinner().getFoodName()+"  引用地址："+user2.getHavingDinner());
    }
}

结果：

哈比-->今天晚上要吃青椒炒萝卜  引用地址：com.demo.cs.study.clones.HavingDinner@12a3a380
哈比2-->今天晚上要吃青椒炒萝卜  引用地址：com.demo.cs.study.clones.HavingDinner@12a3a380
哈士奇-->今天晚上要吃青椒炒萝卜  引用地址：com.demo.cs.study.clones.HavingDinner@12a3a380

看输出结果，引用地址一样。这就是浅克隆；那么问题来了，哈比要吃土豆鸡块，我们改下

Demo2

public class Demo {
    public static void main(String[] args) throws CloneNotSupportedException {
        HavingDinner hd=new HavingDinner("土豆鸡块");
        User user=new User();
        user.setUserName("哈比");
        user.setHavingDinner(hd);
        User user1= (User) user.clone();
        user1.setUserName("哈比2");
        User user2= (User) user.clone();
        user2.setUserName("哈士奇");
        System.out.println(user.getUserName()+"-->今天晚上要吃"+user.getHavingDinner().getFoodName()+"  引用地址："+user.getHavingDinner());
        System.out.println(user1.getUserName()+"-->今天晚上要吃"+user1.getHavingDinner().getFoodName()+"  引用地址："+user1.getHavingDinner());
        System.out.println(user2.getUserName()+"-->今天晚上要吃"+user2.getHavingDinner().getFoodName()+"  引用地址："+user2.getHavingDinner());
    }
}

结果：

哈比-->今天晚上要吃土豆鸡块  引用地址：com.demo.cs.study.clones.HavingDinner@12a3a380
哈比2-->今天晚上要吃土豆鸡块  引用地址：com.demo.cs.study.clones.HavingDinner@12a3a380
哈士奇-->今天晚上要吃土豆鸡块  引用地址：com.demo.cs.study.clones.HavingDinner@12a3a380

会发现其它人都给吃土豆鸡块了，我们再改下哈比2的试试

Demo3：

public class Demo {
    public static void main(String[] args) throws CloneNotSupportedException {
        HavingDinner hd=new HavingDinner("土豆鸡块");
        User user=new User();
        user.setUserName("哈比");
        user.setHavingDinner(hd);
        User user1= (User) user.clone();
        user1.setUserName("哈比2");
        user1.getHavingDinner().setFoodName("冰淇淋");
        User user2= (User) user.clone();
        user2.setUserName("哈士奇");
        System.out.println(user.getUserName()+"-->今天晚上要吃"+user.getHavingDinner().getFoodName()+"  引用地址："+user.getHavingDinner());
        System.out.println(user1.getUserName()+"-->今天晚上要吃"+user1.getHavingDinner().getFoodName()+"  引用地址："+user1.getHavingDinner());
        System.out.println(user2.getUserName()+"-->今天晚上要吃"+user2.getHavingDinner().getFoodName()+"  引用地址："+user2.getHavingDinner());
    }
}

结果：

哈比-->今天晚上要吃冰淇淋  引用地址：com.demo.cs.study.clones.HavingDinner@12a3a380
哈比2-->今天晚上要吃冰淇淋  引用地址：com.demo.cs.study.clones.HavingDinner@12a3a380
哈士奇-->今天晚上要吃冰淇淋  引用地址：com.demo.cs.study.clones.HavingDinner@12a3a380

结果还是都吃冰淇淋，这样的话就有问题了，我想哈比吃土豆鸡块，哈比2吃冰淇淋；
这样也证实了上面的概念；基本属性的值是复制了，但是其它对象里的属性根本就没有复制，只是单纯的复制了引用地址；

2、深克隆

User.java

public class User implements Cloneable{

    private String userName;

    private HavingDinner havingDinner;

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public HavingDinner getHavingDinner() {
        return havingDinner;
    }

    public void setHavingDinner(HavingDinner havingDinner) {
        this.havingDinner = havingDinner;
    }

    @Override
    protected Object clone() throws CloneNotSupportedException{
        User user=(User) super.clone();
        user.setHavingDinner((HavingDinner) getHavingDinner().clone());
        return user;
    }
}

HavingDinner.java

public class HavingDinner implements Cloneable{

    private String foodName;

    public String getFoodName() {
        return foodName;
    }

    public void setFoodName(String foodName) {
        this.foodName = foodName;
    }

    public HavingDinner(String foodName) {
        this.foodName = foodName;
    }

    @Override
    protected Object clone() throws CloneNotSupportedException{
        return super.clone();
    }
}

Demo.java

public class Demo {
    public static void main(String[] args) throws CloneNotSupportedException {
        HavingDinner hd=new HavingDinner("土豆鸡块");
        User user=new User();
        user.setUserName("哈比");
        user.setHavingDinner(hd);
        User user1= (User) user.clone();
        user1.setUserName("哈比2");
        user1.getHavingDinner().setFoodName("冰淇淋");
        User user2= (User) user.clone();
        user2.setUserName("哈士奇");
        System.out.println(user.getUserName()+"-->今天晚上要吃"+user.getHavingDinner().getFoodName()+"  引用地址："+user.getHavingDinner());
        System.out.println(user1.getUserName()+"-->今天晚上要吃"+user1.getHavingDinner().getFoodName()+"  引用地址："+user1.getHavingDinner());
        System.out.println(user2.getUserName()+"-->今天晚上要吃"+user2.getHavingDinner().getFoodName()+"  引用地址："+user2.getHavingDinner());
    }
}

结果：

哈比-->今天晚上要吃土豆鸡块  引用地址：com.demo.cs.study.clones.HavingDinner@12a3a380
哈比2-->今天晚上要吃冰淇淋  引用地址：com.demo.cs.study.clones.HavingDinner@29453f44
哈士奇-->今天晚上要吃土豆鸡块  引用地址：com.demo.cs.study.clones.HavingDinner@5cad8086

总结：达到了互不影响的结果，对象里面包含的对象也复制了，这是第一种方式，有点复杂；
2、序列化深克隆
原理：把对象序列化输出到流里面，然后把流里面的数据序列化出来，得到一个新的对象
事例：
User.java

public class User implements Serializable {

    private String userName;

    private HavingDinner havingDinner;

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public HavingDinner getHavingDinner() {
        return havingDinner;
    }

    public void setHavingDinner(HavingDinner havingDinner) {
        this.havingDinner = havingDinner;
    }

    protected User deepClone() throws IOException, ClassNotFoundException {
        ByteArrayOutputStream byteArrayOutputStream=new ByteArrayOutputStream();
        ObjectOutputStream objectOutputStream=new ObjectOutputStream(byteArrayOutputStream);
        objectOutputStream.writeObject(this);
        ByteArrayInputStream byteArrayInputStream=new ByteArrayInputStream(byteArrayOutputStream.toByteArray());
        ObjectInputStream objectInputStream=new ObjectInputStream(byteArrayInputStream);
        return (User) objectInputStream.readObject();
    }
}

HavingDinner.java

public class HavingDinner implements Serializable {

    private String foodName;

    public String getFoodName() {
        return foodName;
    }

    public void setFoodName(String foodName) {
        this.foodName = foodName;
    }

    public HavingDinner(String foodName) {
        this.foodName = foodName;
    }
}

测试类

public class Demo {
    public static void main(String[] args) throws IOException, ClassNotFoundException {
        HavingDinner hd=new HavingDinner("土豆鸡块");
        User user=new User();
        user.setUserName("哈比");
        user.setHavingDinner(hd);
        User user1=user.deepClone();
        user1.setUserName("哈比2");
        user1.getHavingDinner().setFoodName("冰淇淋");
        User user2=user.deepClone();
        user2.setUserName("哈士奇");
        System.out.println(user.getUserName()+"-->今天晚上要吃"+user.getHavingDinner().getFoodName()+"  引用地址："+user.getHavingDinner());
        System.out.println(user1.getUserName()+"-->今天晚上要吃"+user1.getHavingDinner().getFoodName()+"  引用地址："+user1.getHavingDinner());
        System.out.println(user2.getUserName()+"-->今天晚上要吃"+user2.getHavingDinner().getFoodName()+"  引用地址："+user2.getHavingDinner());
    }
}

结果：

哈比-->今天晚上要吃土豆鸡块  引用地址：com.demo.cs.study.clones.HavingDinner@5e2de80c
哈比2-->今天晚上要吃冰淇淋  引用地址：com.demo.cs.study.clones.HavingDinner@34a245ab
哈士奇-->今天晚上要吃土豆鸡块  引用地址：com.demo.cs.study.clones.HavingDinner@7cc355be

深克隆与浅克隆

一、克隆的作用

二、克隆基本简介

1、浅克隆

2、深克隆

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