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Start your free trialJacob Schoeneman
2,725 PointsJava Null Pointer Exception?
My wrapping up for some reason has a Null Pointer Exception and i don't know why?
public class ForumPost {
private User mAuthor;
private String mTitle;
private String mDescription;
public ForumPost(User author, String title, String description){
User mAuthor = author;
mTitle = title;
mDescription = description;
}
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) {
// TODO: Set the private fields here
mFirstName = firstName;
mLastName = lastName;
}
public String getFirstName(){
return mFirstName;
}
public String getLastName(){
return mLastName;
}
}
public class Forum {
private String mTopic;
public String getTopic() {
return mTopic;
}
public Forum(String topic){
mTopic = topic;
}
public void addPost(ForumPost post) {
// When all is ready uncomment this...
System.out.printf("New post from %s %s about %s \n and %s",
post.getAuthor().getFirstName(),
post.getAuthor().getLastName(),
post.getTitle(),
post.getDescription());
}
}
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, "Finishing", "Finished Java Objects Course");
forum.addPost(post);
}
}
2 Answers
Kourosh Raeen
23,733 PointsThe problem is in the ForumPost constructor. You need to assign the passed in author to mAuthor, which is already defined as private member variable, but you are redefining it:
public ForumPost(User author, String title, String description){
mAuthor = author;
mTitle = title;
mDescription = description;
}
jcorum
71,830 PointsIn your constructor for ForumPost you have an extra User:
public ForumPost(User author, String title, String description){
//User mAuthor = author; //can't have a type here
mAuthor = author;
mTitle = title;
mDescription = description;
}
With the User deleted it will work fine.
Jacob Schoeneman
2,725 PointsJacob Schoeneman
2,725 PointsThanks for the help