Java deep copy and shallow copy

In Java, List is an interface, and the common implementation classes are ArrayList and LinkedList. When we need to copy a List, there are usually two methods: shallow copy and deep copy. A shallow copy only copies the references in the List, while a deep copy copies all the elements in the List. Let's take a look at how to implement a deep copy of List.

Suppose we have a Person class with two properties named and age:

csharp
public class Person {
    private String name;
    private int age;

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

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }
}

Now we have a List that contains some Person objects:

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

public class DeepCopyExample {
    public static void main(String[] args) {
        List<Person> list = new ArrayList<>();
        list.add(new Person("Tom", 18));
        list.add(new Person("Jerry", 20));
        list.add(new Person("Mike", 22));
        System.out.println("Original list: " + list);
    }
}

To implement a deep copy of List, you can use the constructor of java.util.ArrayList:

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

public class DeepCopyExample {
    public static void main(String[] args) {
        List<Person> list = new ArrayList<>();
        list.add(new Person("Tom", 18));
        list.add(new Person("Jerry", 20));
        list.add(new Person("Mike", 22));
        System.out.println("Original list: " + list);

        // 深拷贝
        List<Person> copy = new ArrayList<>(list);
        System.out.println("Copy list: " + copy);
    }
}

In the above code, we use the constructor of ArrayList to create a new List and pass the original list as a parameter. The new list thus created is a deep copy of the original list.