Java对象的深拷贝和浅拷贝

浅拷贝：对象中的基本类型进行值拷贝，引用类型对引用地址进行拷贝。

深拷贝：对象中的基本类型和引用类型对应的值都进行拷贝。

 

注意：不管是深拷贝还是浅拷贝，拷贝之后，两个对象的hashcode 不同，而且equels() 返回也是false。

 

 

java 实现浅拷贝： 必须实现Cloneable 接口，并且重写Object 的clone()

 

public class ShallowCopy implements Cloneable {

    private String name;
    private int age;

    public void hashMapCopy() {
        Map<String, Object> map = new HashMap<String, Object>();
        Map<String, Object> map1 = new HashMap<String, Object>(map);
    }

    /**
     * 浅拷贝,且必须要实现Cloneable接口
     * *
     */
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }


    @Override
    public String toString() {
        return "ShallowCopy{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

 

java实现深拷贝：通过继承Serializable接口，然后使用InputStream 和OutputStream 构造一个新的对象

 

public class DeepCopy {

    public static Object deepCopy(Object obj) {
        try {
            ByteArrayOutputStream bo = new ByteArrayOutputStream();
            ObjectOutputStream objectOutputStream = new ObjectOutputStream(bo);
            objectOutputStream.writeObject(obj);

            ByteArrayInputStream bio = new ByteArrayInputStream(bo.toByteArray());
            ObjectInputStream objectInputStream = new ObjectInputStream(bio);

            return objectInputStream.readObject();

        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        return null;
    }

    public static void main(String[] args) {
        User user = new User("zhangsan", 23);
        User user1 = (User) DeepCopy.deepCopy(user);

        System.out.println("user hashcode:" + user.hashCode());
        System.out.println("user1 hashcode:" + user1.hashCode());

        System.out.println("==" + user.equals(user1));
        System.out.println("user:" + user.toString());
        System.out.println("user1:" + user1.toString());
        /**

         运行结果:
         user hashcode:1426979015
         user1 hashcode:1743450717
         ==false
         user:User{name='zhangsan', age=23}
         user1:User{name='zhangsan', age=23}
         */

    }
}

class User implements Serializable {

    private String name;
    private int age;

    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}