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Start your free trialArmin 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 couldnยดt 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!