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Java Java Objects Delivering the MVP Forum

Task 4 of challenge uncomment comments

I have tried everything i keep getting an error not sure what i am doing wrong

This is the error: Are you sure you used the arguments passed in from the main method in Main.java? args[0] is the firstName and args[1] should be the last name

Forum.java
public class Forum {
  private String topic;


  // TODO: add a constructor that accepts a topic and sets the private field topic
public Forum(String topic) {
//set mTopic to the topic passed in to the constructor
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",
            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
    firstName = firstName;
    lastName = lastName;
  }

  // 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 ForumPost(User author, String title, String description) {
    this.author = author;
    this.title = title;
    this.description = description;
  }

  public User getAuthor() {
    return author;
  }

  public String getTitle() {
    return title;
  }

  public String getDescription() {
    return description;
  }
}
Main.java
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");

    String firstName = args[0];
    String lastName = args[1];
    User author = new User(firstName, lastName);

    ForumPost post = new ForumPost(author, "Programming is awesome", "Cuz it makes us create new stuff");
    forum.addPost(post);


  }


}

1 Answer

andren
andren
28,538 Points

The issue is the constructor you have written for the Forum and User class.

Take a look at the constructor for ForumPost (which is correct):

public ForumPost(User author, String title, String description) {
    this.author = author;
    this.title = title;
    this.description = description;
}

And then compare it to the constructor for User (which is incorrect):

public User(String firstName, String lastName) {
    // TODO: set and add the private fields
    firstName = firstName;
    lastName = lastName;
}

Can you notice any difference between those two constructors beyond the names used?

The difference is the lack of the this keyword. When you have a field variable and a parameter that has the same name, you have to use the this keyword to help Java distinguish between the two.

So you have to change the User constructor like this:

public User(String firstName, String lastName) {
    // TODO: set and add the private fields
    this.firstName = firstName;
    this.lastName = lastName;
}

The same issue applies to the Forum constructor, which also has to be fixed like this:

public Forum(String topic) {
    //set mTopic to the topic passed in to the constructor
    this.topic = topic;
}

Once you fix those constructors your code should work fine.

Awesome it actually worked thank you