Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

Java Java Objects Delivering the MVP Forum

java.lang.NullPointerException (Look around Forum.java line 17)

Hi everyone. I am struggling with the last part of this challenge for over one hour. It alway says: Bummer! java.lang.NullPointerException (Look around Forum.java line 17), but everything I had to do there was to uncomment the code. I did also check the previous Java Objects Course and since it is not exactly 100% the same code, I couldn´t figure it out here. I really appreciate your help!

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) {
    topic = topic;
  }

  public String getTopic() {
    return topic;
  }

  public void addPost(ForumPost post) {
    System.out.printf("A new post in %s topic from %s %s about %s is available\n", 
                      topic, 
                      post.getAuthor().getFirstName(),
                      post.getAuthor().getLastName(),
                      post.getTitle()
    );
  }


}
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
    firstName = firstName;
    lastName = lastName;
  }

  public String getFirstName() {
    return firstName;
  }

  public String getLastName() {
    return lastName;
  }

  // TODO: add getters for firstName and 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) {
    author = author;
    title = title;
    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);
    }

    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");
    forum.addPost(post);

  }

}

2 Answers

Kourosh Raeen
Kourosh Raeen
23,733 Points

Hi Armin - In the constructors for the Forum, the ForumPost and the User classes you need to use the this keyword to distinguish between the class variables and the arguments passed into the constructors:

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

and

public User(String firstName, String lastName) {
    // TODO: set and add the private fields
    this.firstName = firstName;
    this.lastName = lastName;
  }

and

// 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;
  }

Kourosh Raeen

Thank you , it worked!

Kourosh Raeen
Kourosh Raeen
23,733 Points

Glad I could help! Happy coding!