How to iterate inside a list that is inside another class?

Question

I wonder if it is possible to iterate a list that is in another class. On a social network, every user has a list of posts, but this list is defined only in the class User how to iterate inside it ? Method I want to apply:

rede.addComment ("u3", "u1", "p1", new Comment ("c1", 
                 "Com pão de queijo ? tudo di bão"));

Class SocialNetwork:

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

public class SocialNetwork {

    private List<User> users;

    public SocialNetwork () {
        users = new ArrayList<User>();
    }

    public void addUser(User user) { 
        users.add(user);        
    }

    public User getUserById(String id) {

        for (User u : users) {
            if (id == u.getId())
                return u;
        }

        return null;

    }

    private Post getPostById(Post post, User id) {
        for (User getUserById(id) i : posts) {

        }
        return null;
    }

    public void addPost(String id, Post post) {
        User userId = getUserById(id);
        userId.addPost(post);
    }

    public void addComment(String user1, String user2, String postId, Comment comment) {
        User userComented = getUserById(user1);
        User userPosted = getUserById(user2);
        Post post = getPostById(postId);

    }}

Class User:

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

public class User {

    private String id;
    private String name;
    private List<User> friends;
    private List<Post> posts;

    public User(String id, String name) {
        this.id = id;
        this.name = name;
        friends = new ArrayList<>();
        posts = new ArrayList<>();
    }

    public void addFriend (User friend) {
        friends.add(friend);
    }

    public void addPost (Post post) {
        posts.add(post);
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public List<Post> getUserPosts() {
        return this.posts;
    }

    @Override
    public String toString() {
        return "(" + id +"," + name +")";
    }}

Class Post:

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

public class Post {

    private String id;
    private String content;
    private List<Comment> comments;
    private List<String> likes;

    public Post(String id, String content) {
        this.id = id;
        this.content = content;
        comments = new ArrayList<>();
        likes = new ArrayList<>();
    }

    public String getId() {
        return id;
    }

    public String getContent() {
        return content;
    }

    public void addComment (Comment comment) {
        comments.add(comment);
    }}

Answer 1

Hello, Breno!

Get the class list User as follows

User user = new User();
List<Post> posts = user.getUserPosts();

Now you can use the list of Postas you wish

for(Post p: posts) {
   // p é um objeto, use sua função aqui
}

But if somehow, you really want to do it within your class User, can create a method that does this job

public class User {
    List<Post> posts;

    /*...*/

    public void setPosts(List<Post> posts) {
       this.posts = posts;
    }

    /*...*/

    public void postsIterator(SocialNetwork network) {
       for(Post p: this.posts) {
          network.addComment(); // seu método aqui
        }
    }
}

And then just pass an instance of your class SocialNetwork and call your method to process posts. I hope it helps!