Java Java Objects Delivering the MVP Forum

unknown error

this code will not run and the compiler is not pointing to the bug, i cant figure out what the problem is

Forum.java
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 getTopic() {
    return topic;
  }


  // Uncomment this when you are prompted to do so

  public void addPost(ForumPost post) {
    System.out.printf("%s %s has a new post in %s topic in %s available",
            post.getAuthor().getFirstName(),
            post.getAuthor().getLastName(),
            post.getTitle(),
                     topic);
  }

  }
User.java
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;
  }

}
ForumPost.java
public class ForumPost {
  private User author;
  private String title;
  private String description;


  // TODO: add a constructor that accepts the author, title and 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;
  }
}
Main.java
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);
    }

    // Uncomment this when prompted

    Forum forum = new Forum("java");

    // TODO: pass in the first name and last name that are in the args parameter

     User author = new User(args[0],args[1]); 

    // TODO: initialize the forum post with the user created above and a title and description of your choice

    ForumPost post = new ForumPost(author,"java objects","java objects");
    forum.addPost(post);


  }

}