my code isnt work and im doing everthing right

public class Forum {
  private String topic;

  // TODO: add a constructor that accepts a topic and sets the private field topic



  public  Forum(String topic){

    this.topic = topic;


  }
  public String setTopic() {
    return topic;
  }


  // Uncomment this when you are prompted to do so
  public void addPost(ForumPost post) {
    System.out.printf("A new post in %s topic from %s %s about %s is available",
            topic,
            post.getAuthor().getFirstName(),
            post.getAuthor().getLastName(),
            post.getTitle()
    );
  }


}

public class User {
  // TODO: add private fields for firstName and lastName

  private String firstName;
  private String lastName;

  public User(String firstName, String lastName) {
    // TODO: set and add the private fields

    this.firstName = firstName;
    this.lastName = lastName;

  }

  // TODO: add getters for firstName and lastName

  public String getFirstName(){
    return firstName;
  }


  public String getLastName(){
    return lastName;

  }

}

public class ForumPost {
  private User author;
  private String title;
  private String description;

  public ForumPost(User author, String title, String description){

    this.author = author;
    this.title = title;
    this.description = description;



  }

  // TODO: add a constructor that accepts the author, title and description


}

public class Main {

  public static void main(String[] args) {
   System.out.println("Beginning forum example");
    if (args.length < 2) {
      System.out.println("Usage: java Main <first name> <last name>");
      System.err.println("<first name> and <last name> are required");
      System.exit(1);
    }

    Forum forum = new Forum("Java");
    // TODO: pass in the first name and last name that are in the args parameter

    User author = new User("jyfjfh", "utyfygh"); //<----- all cruicial points marked with comments
    // TODO: initialize the forum post with the user created above and a title and description of your choice

    ForumPost post = new ForumPost(author, "Programming is awesome", "Cuz it makes us create new stuff");
    forum.addPost(post);

  }

}