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Java Java Objects (Retired) Delivering the MVP Wrapping up

Posted by Gonzalo Nunez
Gonzalo Nunez
Courses Plus Student 5,064 Points

Can´t pass this quiz, even with the correct answers.

When I uncomment the code block, this error shows: java.lang.NullPointerException (Look around Forum.java line 11).

If I don´t uncomment, the console says that I have to uncomment the forum.addPost(post); which is uncomment in the code.

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

  public User getAuthor() {
    return mAuthor;
  }

  public String getTitle() {
    return mTitle;
  }
  public String getDescription() {
    return mDescription;
  }

 public ForumPost(User author, String title, String description){

//add these in the constructor to actually make sure your variables are being stored
   author  = mAuthor;
   title = mTitle;
   description = mDescription;
}
}
User.java 
public class User {
  private String mFirstName;
  private String mLastName;

  public User(String firstName, String lastName) {
      mFirstName = firstName;
      mLastName = lastName;
  }

  public void setFirstName(String firstName) {
       mFirstName = firstName;
  }

  public void setLastName(String lastName) {
       mLastName = lastName;
  }

  public String getFirstName() {
      return mFirstName;
  }

   public String getLastName() {
       return mLastName;
   }
}
Forum.java 
public class Forum {
  private String mTopic;

  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());

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

  }
}
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 author = new User(args[0], args[1]);
    // Add the author, title and description
     ForumPost post = new ForumPost(author, "Rafael", "Awesome" );
     forum.addPost(post);
  }
}

2 Answers

Jeremy Hill
Jeremy Hill
29,567 Points

For starters I would change the variables in your constructor in ForumPost to look like this:

public ForumPost(User author, String title, String description){
   mAuthor  = author;
   mTitle = title;
   mDescription = description;
}
Jeremy Hill
Jeremy Hill
29,567 Points

You might also put all of your methods under your constructor (getAuthor, getTitle, getDescription, etc.)

anil rahman
anil rahman
7,786 Points
anil rahman
anil rahman
7,786 Points

Yes once he changes his variables in the constructor should work.

Gonzalo Nunez
Gonzalo Nunez
Courses Plus Student 5,064 Points

Thanks!

anil rahman
anil rahman
7,786 Points
anil rahman
anil rahman
7,786 Points

There fully works :) Compare to yours and check all details.

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 author = new User(args[0],args[1]);
     //Add the author, title and description
     ForumPost post = new ForumPost(author,"hello","world");
     forum.addPost(post);
  }
}

Forum.java

public class Forum {
  private String mTopic;

  public String getTopic() {
      return mTopic;
  }

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

  public String getDescription(){
    return mDescription; 
  }

  public User getAuthor() {
    return mAuthor;
  }

  public String getTitle() {
    return mTitle;
  }

  // TODO: We need to expose the description
}