Java深拷贝和浅拷贝

• 浅拷贝：浅拷贝会在堆上创建一个新的对象（区别于引用拷贝的一点），不过，如果原对象内部的属性是引用类型的话，浅拷贝会直接复制内部对象的引用地址，也就是说拷贝对象和原对象共用同一个内部对象。
• 深拷贝 ：深拷贝会完全复制整个对象，包括这个对象所包含的内部对象。

下面我写了一个样例解释深拷贝和浅拷贝：

这个样例中有两个类，一个Person类，一个Address类，Person类中有一个内部对象Address

首先是浅拷贝

public class Person implements Cloneable{
    private String name;
    private  Address address;
    public Person (String name ,Address address){
        this.name = name; this.address = address;
    }
    public String getName() {
        return name;
    }
    public Address getAddress() {
        return address;
    }
    @Override
    protected Object clone() throws CloneNotSupportedException {
        Person person =  (Person) super.clone();
        return person;
    }


    public static void main(String[] args) throws Exception {
        Address address = new Address("北京");
        Person person = new Person("小明",address);
        Person person2  = (Person) person.clone();
        System.out.println(person == person2);
        System.out.println(person.getAddress() == person2.getAddress());
    }
}

class Address {
    private String city;
    public Address(String city){
        this.city = city;
    }
    public void setCity(String city){
        this.city = city;
    }
    public String getCity(){
        return this.city;
    }
 
}

输出的结果为：
false true

我们比较person的内部对象的引用address和克隆出来的person1的内部对象的引用address时，它们竟然是相等的，说明它们指向堆中的同一对象；

那么说明我们修改person中的address时，person1的address也会被修改

//修改person
person.getAddress().setCity("上海");
//查看person2是否被修改
System.out.println(person2.getAddress().getCity());

输出结果为：上海 ； 说明person2也被修改了

下面是浅拷贝的样例图

那么我们如何实现深拷贝呢，也就是让person中的内部address指向堆中不同的对象

我们只需要将每个引用类型的属性实现Cloneable接口，并且重写clone方法即可

public class Person implements Cloneable{
    private String name;
    private  Address address;
    public Person (String name ,Address address){
        this.name = name; this.address = address;
    }
    public String getName() {
        return name;
    }
    public Address getAddress() {
        return address;
    }
    @Override
    protected Object clone() throws CloneNotSupportedException {
        Person person =  (Person) super.clone();
        person.address = (Address) address.clone();
        return person;
    }


    public static void main(String[] args) throws Exception {
        Address address = new Address("北京");
        Person person = new Person("小明",address);
        Person person2  = (Person) person.clone();
        System.out.println(person == person2);
        System.out.println(person.getAddress() == person2.getAddress());

        person.getAddress().setCity("上海");
        System.out.println(person2.getAddress().getCity());

    }
}

class Address implements Cloneable{
    private String city;
    public Address(String city){
        this.city = city;
    }
    public void setCity(String city){
        this.city = city;
    }
    public String getCity(){
        return this.city;
    }
    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

输出结果为：false false 北京

下面是深拷贝的样例图