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Michael Lee
2,541 PointsI'm getting an error of "java.lang.NullPointerException (Look around Forum.java line 16)"
I think it may be a problem with my User class, but I cannot figure out what the problem is.
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;
}
// TODO: We need to expose the description
public ForumPost(User mAuthor, String mTitle, String mDescription) {
}
}
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;
}
}
public class Forum {
public Forum(String topic) {
mTopic = topic;
}
private String mTopic;
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());
}
}
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, "Done", "It feels great!");
forum.addPost(post);
}
}
2 Answers
Michael Hess
24,512 PointsHi Michael,
The constructor in forumPost.java doesn't have member variables declared in the constructor.
public class ForumPost {
private User mAuthor;
private String mTitle;
private String mDescription;
//add this constructor
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;
}
}
If you have any questions -- feel free to ask!
Phillip Hurst
4,204 PointsI had the following:
author = mAuthor; title = mTitle; description = mDescription;
These were acceptable in the step of the challenge that called them out... but when I got to the last step it failed for a similar error message as the OP.
I reversed them to have the member variable first instead of second and the last step of the challenge passed.
Is this a limitation of the challenge checker? I am not sure if there is a correct order to setting objects equal to...
Michael Hess
24,512 PointsHi Phillip Hurst,
If you think there is a bug you can contact the member support team and they will look into it. The directions for reporting a bug are outlined here: report a bug.
//The member variables are written first
public ForumPost(User author, String title, String description) {
mAuthor = author;
mTitle = title;
mDescription = description;
}
// This is incorrect
public ForumPost(User author, String title, String description) {
author = mAuthor;
title = mTitle;
description = mDescription;
}
Hope this helps!