illegal start of expression cannot find symbol syntax errors

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

  // TODO: add a constructor that accepts a topic and sets the private field top
  public Forum(String topic) {
    this.topic;
  }

  public String getTopic() {
    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;
  }
  public String getFirstName() {
    return firstName;
  }
  public String getLastName() {
    return lastName;

  }
  // TODO: add getters for firstName and 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);
    }
    public void addPost(ForumPost post) {
      System.out.printf("A new post in %s topic from %s %s about %s is available %s"
                       topic,
                       post.getAuthor().getFirstName(),
                       post.getAuthor().getLastName(),
                       post.getTitle()

                      );
  }
}