对象中的clone方法（深拷贝与浅拷贝）

java.lang.Object 中的有一个clone方法，这个方法在不重写的方法的情况下其实是浅拷贝。

对基本数据类型是值传递，对引用数据类型进行的是引用传递的拷贝。

是对基本数据类型值传递，对数据类型创建一个新的对象，并复制其内容

示例代码：

public class CloneDemo implements Cloneable{
    private String name;
    private int age;
    private Address address;
    public CloneDemo(String name, int age, Address address) {
        this.name = name;
        this.age = age;
        this.address = address;
    }
    public Address getAddress() {
        return address;
    }
    public void setAddress(Address address) {
        this.address = address;
    }
    @Override
    public String toString() {
        return "CloneDemo{" +
                "name='" + name + ''' +
                ", age=" + age +
                ", address=" + address +
                '}';
    }
    public static void main(String[] args) throws CloneNotSupportedException {

        CloneDemo cloneDemo = new CloneDemo("Song", 22,new Address("上海"));
        CloneDemo cloneDemo1 = (CloneDemo)cloneDemo.clone();
        cloneDemo1.getAddress().setProvince("北京");
        System.out.println(cloneDemo);
        System.out.println(cloneDemo1);
    }
}
class Address {
    private String province;

    public Address(String province) {
        this.province = province;
    }

    public String getProvince() {
        return province;
    }
    public void setProvince(String province) {
        this.province = province;
    }

    @Override
    public String toString() {
        return "Address{" +
                "province='" + province + ''' +
                '}';
    }
}

运行结果：

CloneDemo{name='Song', age=22, address=Address{province='北京'}}
CloneDemo{name='Song', age=22, address=Address{province='北京'}}

以上就是浅拷贝的现象，那么如何实现深拷贝呢？
最简单的方法就是重写clone()方法

public class CloneDemo implements Cloneable{
    private String name;
    private int age;
    private Address address;
    public CloneDemo(String name, int age, Address address) {
        this.name = name;
        this.age = age;
        this.address = address;
    }
    public Address getAddress() {
        return address;
    }
    public void setAddress(Address address) {
        this.address = address;
    }
    @Override
    public String toString() {
        return "CloneDemo{" +
                "name='" + name + ''' +
                ", age=" + age +
                ", address=" + address +
                '}';
    }
    public static void main(String[] args) throws CloneNotSupportedException {

        CloneDemo cloneDemo = new CloneDemo("Song", 22,new Address("上海"));
        CloneDemo cloneDemo1 = cloneDemo.clone();
        cloneDemo1.getAddress().setProvince("北京");
        System.out.println(cloneDemo);
        System.out.println(cloneDemo1);
    }

    @Override
    public CloneDemo clone() {
        try {
            CloneDemo clone = (CloneDemo) super.clone();
            clone.setAddress(address.clone());
            return clone;
        } catch (CloneNotSupportedException e) {
            throw new AssertionError();
        }
    }
}


class Address implements Cloneable{
    private String province;

    public Address(String province) {
        this.province = province;
    }

    public String getProvince() {
        return province;
    }
    public void setProvince(String province) {
        this.province = province;
    }

    @Override
    public String toString() {
        return "Address{" +
                "province='" + province + ''' +
                '}';
    }

    @Override
    public Address clone() {
        try {
            return(Address) super.clone();
        } catch (CloneNotSupportedException e) {
            throw new AssertionError();
        }
    }
}

运行结果：

CloneDemo{name='Song', age=22, address=Address{province='上海'}}
CloneDemo{name='Song', age=22, address=Address{province='北京'}}

重写clone()方法的确可以实现对象的深拷贝，但是这种方法的缺点也是显而易见。
1、使用Fastjson

public class Main {
    public static void main(String[] args) {
        User user = new User();
        user.setName("Song");

        User user1 = JSON.parseObject(JSON.toJSONString(user), User.class);
        user1.setAge(22);

        System.out.println(user);
        System.out.println(user1);
    }
}

@Data
public class User {
    private String name;
    private int age;
}

运行结果

User(name=Song, age=0)
User(name=Song, age=22)

2、使用 Apache Commons Lang 包中的SerializationUtils 在使用改工具时必须将实体类序列化

import org.apache.commons.lang3.SerializationUtils;

public class Main {
    public static void main(String[] args) {
        User user = new User();
        user.setName("Song");

        User user1 = SerializationUtils.clone(user);
        user1.setAge(22);

        System.out.println(user);
        System.out.println(user1);
    }
}

The End ！！！