I'm getting a null exception at line 19. Not sure what to do here.

Question

I looked up the answer to several other questions that are similar and I can't find what I'm doing wrong here. I'm not really sure how to solve this question. It's a small error somewhere, but I can't seem to find it.

Thanks

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 getTopic) {
    this.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 ",
            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
      this.firstName = firstName;
      this.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;

  public ForumPost(User getAuthor, String getTitle, String getDescription) {
    this.author = author;
    this.title = title;
    this.description = description;
  }
  // TODO: add a constructor that accepts the author, title and 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");
    String firstName = args[0];
    String lastName = args[1];

    User author = new User(firstName, lastName);

    ForumPost post = new ForumPost(author, "Its a short post", "Thanks for being great and stuff");
    forum.addPost(post);

  }

}

Answer 1 · 2017-07-20T20:42:57Z

July 20, 2017 8:42pm

The issue is the names you give to parameters within the various constructors. Take the Forum constructor for example:

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

Within the constructor you are meant to tell Java to set the topic field variable equal to the parameter that got passed into the constructor. But you have named the parameter getTopic, not topic which is the name your code references.

If you changed the name like this:

public Forum(String topic) { // getTopic changed to topic
    this.topic = topic;
}

Then that code would work.

The same issue is present in the constructor for the ForumPost class as well and has to be fixed in the same way like this:

public ForumPost(User author, String title, String description) {
    this.author = author;
    this.title = title;
    this.description = description;
  }

Welcome to the Treehouse Community

Looking to learn something new?

Jonas Troyer

Jonas Troyer

I'm getting a null exception at line 19. Not sure what to do here.

1 Answer

andren

andren