Keep getting the cannot find symbol error for forum.addPost(post);

public class Forum {
  private String topic;

  public Forum (String topic) 
  {
    this.topic = topic; 
  }

  public String getTopic() {
    return topic;
  }
}

public class User {
  private String firstName;
  private String lastName;

  public User(String firstName, String lastName) {
    this.firstName = firstName; 
    this.lastName = 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;
    }

  public User getAuthor() {
    return author;
  }

  public String getTitle() {
    return title;
  }

  public String getDescription() {
    return 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");
    String firstName = args[0];
    String lastName = args[1];
    User author = new User(args[0], args[1]); 
    ForumPost post = new ForumPost(author, "A title", "A description");
    forum.addPost(post);
  }
}