什么是浅拷贝和深拷贝？

• 浅拷贝：只复制指向某个对象的指针，而不复制对象本身，新旧对象共享一块内存；
• 深拷贝：复制并创建一个一摸一样的对象，不共享内存，修改新对象，旧对象保持不变；

浅拷贝
拷贝对象和原始对象的引用类型引用同一个对象。

@Test
public void copyDemo1(){
    User user1 = new User(1,"baili", "baili.com");
    User user2 = user1; // 浅拷贝

    System.out.println("User 1: " + user1);
    System.out.println("User 2: " + user2);

    // 分别修改user对象的属性
    user1.setUsername("百里");
    user2.setEmail("百里.com");

    // 输出修改后的结果
    System.out.println("User 1: " + user1);
    System.out.println("User 2: " + user2);
}

深拷贝
拷贝对象和原始对象的引用类型引用不同对象。

package polo;

import java.util.ArrayList;
import java.util.List;

/**
 * @author 百里
 */
public class Person implements Cloneable {
    private string name;
    private int age;
    private List<String> hobbies;

    public Person(String name, int age, List<String> hobbies) {
        this.name = name;
        this.age = age;
        this.hobbies = hobbies;
    }

    // Getters and setters

    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;
    }

    public List<String> getHobbies() {
        return hobbies;
    }

    public void setHobbies(List<String> hobbies) {
        this.hobbies = hobbies;
    }
    
    @Override
    public Person clone() throws CloneNotSupportedException {
        // 浅拷贝对象
        Person clonedPerson = (Person) super.clone();
        // 深拷贝 List
        clonedPerson.setHobbies(new ArrayList<>(hobbies));
        
        return clonedPerson;
    }

    @Override
    public String toString() {
        return "Person [name=" + name + ", age=" + age + ", hobbies=" + hobbies + "]";
    }
}

@Test
public void copyDemo2(){
    List<String> hobbies = new ArrayList<>();
    hobbies.add("Reading");
    hobbies.add("Gardening");
    Person person1 = new Person("baili", 30, hobbies);

    try {
        Person person2 = person1.clone(); // 深拷贝

        System.out.println("Person 1: " + person1);
        System.out.println("Person 2: " + person2);

        // 修改 person2 的属性
        person2.setName("百里");
        person2.setAge(25);
        person2.getHobbies().add("Cooking");

        // 输出修改后的结果
        System.out.println("Person 1: " + person1);
        System.out.println("Person 2: " + person2);
    } catch (CloneNotSupportedException e) {
        e.printStackTrace();
    }
}

使用 clone() 方法来拷贝一个对象即复杂又有风险，它会抛出异常，并且还需要类型转换。Effective Java 书上讲到，最好不要去使用 clone()，可以使用拷贝构造函数或者拷贝工厂来拷贝一个对象。

使用拷贝构造函数：

class Person {
    private String name;
    private int age;

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

    // 拷贝构造函数
    public Person(Person other) {
        this.name = other.name;
        this.age = other.age;
    }

    // Getters and setters
    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 "Person [name=" + name + ", age=" + age + "]";
    }
}

public class Main {
    public static void main(String[] args) {
        Person person1 = new Person("baili", 30);

        // 使用拷贝构造函数创建 person2 对象
        Person person2 = new Person(person1);

        System.out.println("Person 1: " + person1);
        System.out.println("Person 2: " + person2);

        // 修改 person2 的属性
        person2.setName("BAILI");
        person2.setAge(25);

        // 输出修改后的结果
        System.out.println("Person 1: " + person1);
        System.out.println("Person 2: " + person2);
    }
}

使用拷贝工厂：

class Person {
    private String name;
    private int age;

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

    // Getters and setters

    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 "Person [name=" + name + ", age=" + age + "]";
    }
}

class PersonFactory {
    public static Person createCopy(Person original) {
        // 使用拷贝构造函数创建新的对象
        return new Person(original.getName(), original.getAge());
    }
}

public class Main {
    public static void main(String[] args) {
        Person person1 = new Person("bali", 30);

        // 使用拷贝工厂创建 person2 对象
        Person person2 = PersonFactory.createCopy(person1);

        System.out.println("Person 1: " + person1);
        System.out.println("Person 2: " + person2);

        // 修改 person2 的属性
        person2.setName("BAILI");
        person2.setAge(25);

        // 输出修改后的结果
        System.out.println("Person 1: " + person1);
        System.out.println("Person 2: " + person2);
    }
}