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Start your free trialSmith Thapa
7,023 PointsJava null point exception ? What to do?
Can not solve ...
public class ForumPost {
private User mAuthor;
private String mTitle;
private String mDescription;
public ForumPost(User author, String title, String description){
author = mAuthor;
title=mTitle;
description= mDescription;
}
public User getAuthor() {
return mAuthor;
}
public String getTitle() {
return mTitle;
}
public String getDescription(){
return mDescription;
}
// TODO: We need to expose the description
}
public class User {
private String mFirstName;
private String mLastName;
public User(String firstName, String lastName) {
mFirstName= firstName;
mLastName = lastName;
// TODO: Set the private fields here
}
public String getFirstName(){
return mFirstName;
}
public String getLastName(){
return mLastName;
}
}
public class Forum {
private String mTopic;
public Forum(String topic) {
mTopic = topic;
}
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, "This is your forum post title", "This is your forum post description.");
forum.addPost(post);
}
}
1 Answer
Florian Tönjes
Full Stack JavaScript Techdegree Graduate 50,856 PointsHey Smith,
you get a NullPointerException because you made a mistake in the ForumPost constructor:
...
public ForumPost(User author, String title, String description){
author = mAuthor;
title= mTitle;
description = mDescription;
...
has to be
...
public ForumPost(User author, String title, String description){
mAuthor = author;
mTitle = title;
mDescription= description;
...
Java assigns the value on the right side of the ' = ' assignment operator to the variable on the left side and you want to assign the values in the parameter to the member variables here.
Regards, Florian
Smith Thapa
7,023 PointsSmith Thapa
7,023 PointsThank you so much !