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Start your free trialJohnathan Mullen
1,868 PointsForum
My error Bummer! java.lang.NullPointerException (Look around Forum.java line 18)
public class Forum {
private String topic;
// TODO: add a constructor that accepts a topic and sets the private field topic
public String getTopic() {
return topic;
}
public Forum(String topic){
topic = this.topic;
}
public void addPost(ForumPost post) {
System.out.printf("A new post in %s topic from %s %s about %s is available",
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 = this.firstName;
lastName = this.lastName;
}
// TODO: add getters for firstName and lastName
public String getFirstName(){
return firstName;
}
public String getLastName(){
return 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 User getAuthor() {
return author;
}
public String getTitle() {
return title;
}
public String getDescription() {
return description;
}
public ForumPost(User author, String title, String description){
author = this.author;
title = this.title;
description = this.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","What I am trying to learn!");
forum.addPost(post);
}
}
1 Answer
Mihai Craciun
13,520 PointsBe careful at constructors. It is : this.parameter = parameter;
I've pointed your mistakes in your code below
Forum.java
public class Forum {
private String topic;
// TODO: add a constructor that accepts a topic and sets the private field topic
public String getTopic() {
return topic;
}
public Forum(String topic){
this.topic = topic //<<<----------------------------------------------------- HERE
}
public void addPost(ForumPost post) {
System.out.printf("A new post in %s topic from %s %s about %s is available",
topic,
post.getAuthor().getFirstName(),
post.getAuthor().getLastName(),
post.getTitle()
);
}
}
User.java
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
this.firstName = firstName; //<--------------------------HERE
this.lastName = lastName; //<--------------------------HERE
}
// TODO: add getters for firstName and lastName
public String getFirstName(){
return firstName;
}
public String getLastName(){
return lastName;
}
}
ForumPost.java
public class ForumPost {
private User author;
private String title;
private String description;
// TODO: add a constructor that accepts the author, title and description
public User getAuthor() {
return author;
}
public String getTitle() {
return title;
}
public String getDescription() {
return description;
}
public ForumPost(User author, String title, String description){
this.author = author; //<--------------------------HERE
this.title = title; //<---------------------------HERE
this.description = description; //<----------------HERE
}
}