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Java Java Objects (Retired) Delivering the MVP Wrapping up

Rik-Jan van Bree
Rik-Jan van Bree
1,084 Points
Posted by Rik-Jan van Bree
Rik-Jan van Bree
1,084 Points

Hi, in task 4 of 4, I get a java.lang.NullPointerException at line 15 in class Forum.Java. Can you help me? Thx.

Hi, in challenge 4, I get a null-point exception at line 14 in class Java. Can you help me? Thx.

Here is the code:

Example.java: 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 author1 = new User("Rik-Jan","vanBree"); // Add the author, title and description ForumPost post = new ForumPost(author1 ,"Lean","mgmtsubject"); forum.addPost(post); } }

Forum.Java: public class Forum { private String mTopic;

Forum (String topic){ mTopic=topic; } public String getTopic() { return mTopic; }

public void addPost(ForumPost post) {

  System.out.printf("New post from %s %s about %s.\n",
                     post.getAuthor().getFirstName(),
                     post.getAuthor().getLastName(),
                     post.getTitle());

} }

User.java 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; } }

Forumpost.java public class ForumPost { private User mAuthor; private String mTitle; private String mDescription;

public User getAuthor() { return mAuthor; }

ForumPost (User author, String title, String description){ User mAuthor=author; mTitle = title; mDescription = description; }

public String getDescription(){ return mDescription; }

public String getTitle() { return mTitle; } }

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

  public User getAuthor() {
    return mAuthor;
  }

  ForumPost (User author, String title, String description){
    User mAuthor=author;
    mTitle = title;
    mDescription = description;
  }

  public String getDescription(){
    return mDescription;
  }

  public String getTitle() {
    return mTitle;
  }
}
User.java 
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;
}
}
Forum.java 
public class Forum {
  private String mTopic;

 Forum (String topic){
   mTopic=topic;
 }
  public String getTopic() {
      return mTopic;
  }

  public void addPost(ForumPost post) {

      System.out.printf("New post from %s %s about %s.\n",
                         post.getAuthor().getFirstName(),
                         post.getAuthor().getLastName(),
                         post.getTitle());

  }
}
Example.java 
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 author1 = new User("Rik-Jan","vanBree");
    // Add the author, title and description
    ForumPost post = new ForumPost(author1 ,"Lean","mgmtsubject");
    forum.addPost(post);
  }
}

2 Answers

Jeremy Hill
Jeremy Hill
29,567 Points

I was going to try to pick through your code but because there was so much I figured I would show you mine: It was relatively easy as far as following the instructions. There was just one step that tripped me up- trying to figure out who the authors were supposed to be. I just added the built in args[] to add the users. That actually lets the user type in those parts when they run the program. Anyway just take a look:

// ForumPost***********************************************

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

  public ForumPost(User author, String title, String description){
    mAuthor = author;
    mTitle = title;
    mDescription = description;

  }

  public User getAuthor() {
    return mAuthor;
  }

  public String getTitle() {
    return mTitle;
  }

  public String getDescription(){
    return mDescription; 
  }

  // TODO: We need to expose the description
}

// end ForumPost****************************************************

// class User*******************************************************

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; 
  }
}

// end class User*****************************************************

// class Forum********************************************************

public class Forum {
  private String mTopic;

  public Forum(String topic){

    mTopic = topic;

  }

  public String getTopic() {
      return mTopic;
  }

  public void addPost(ForumPost post) {

      System.out.printf("New post from %s %s about %s.\n",
                         post.getAuthor().getFirstName(),
                         post.getAuthor().getLastName(),
                         post.getTitle());

  }
}

// end class Forum********************************************************

// class Example**********************************************************

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(args[0], args[1]);
    // Add the author, title and description
    ForumPost post = new ForumPost(author, "Hey what's up?", "This course rocks!");
    forum.addPost(post);
  }
}

// end class Example**************************************************************
Jeremy Hill
Jeremy Hill
29,567 Points

No problem, I'm glad you got it :)