Don't see why my Forum constructor is not getting recognized?

public class ForumPost {
  private User mAuthor;
  private String mTitle;
  private String mDescription;

  public User getAuthor() {
    return mAuthor;
  }

  public String getTitle() {
    return mTitle;
  }

  // TODO: We need to expose the description
}

public class User {
  private String mFirstName;
  private String mLastName;
  public User(String firstName, String lastName) {
    // TODO:  Set the private fields here
    mFirstName = firstName;
    mLastName = lastName;
  }
    public String getFirstName() {
      return mFirstName; }
  public String getLastName() {
    return mLastName; }

}

public class Forum {
  private String mTopic;

  Forum forum = new Forum("Brian M", "Cool Breeze", "Chat Session");

  String userauthor;
  String title;
  String description;

  // public String Author(String FirstName, String LastName); 

    public Forum (String userAuthor, String Title, String Description) {
      userauthor = userAuthor;
      title = Title;
      description = Description; }

  public String getTopic() {
      return mTopic;
  }
      public void addPost(ForumPost post) {
         }
            /* When all is ready uncomment this...
      System.out.printf("New post from %s %s about %s.\n",
                         post.getAuthor().getFirstName(),
                         post.getAuthor().getLastName(),
                         post.getTitle());
      */
   //Forum topik = new Forum("JAVA");
   public Forum (String topic) {
    mTopic = topic; }   

  }

public class Example {

  public static void main(String[] args) {
    System.out.println("Starting forum example...");
    if (args.length < 2) {
       System.out.println("first and last name are required. eg:  java Example Craig Dennis");
    }
    // Forum forum = new Forum("Java");
    // Take the first two elements passed args
    // User author = new User();
    // Add the author, title and description
    // ForumPost post = new ForumPost();
    // forum.addPost(post);
  }
}