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Armin Halilovic
19,109 Pointsjava.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!
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()
);
}
}
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
}
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;
}
}
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
23,733 PointsHi 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;
}
Armin Halilovic
19,109 PointsThank you , it worked!
Kourosh Raeen
23,733 PointsGlad I could help! Happy coding!