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Java Java Objects Delivering the MVP Forum

Steven Morimoto
PLUS
Steven Morimoto
Courses Plus Student 1,836 Points
Posted by Steven Morimoto
Steven Morimoto
Courses Plus Student 1,836 Points

I'm able to solve the problem, but I'm still unclear about something

in lines 19 and 20 of the Forum class you bring in the method getAuthor() from the class ForumPost with the object post. That makes sense to me. What I'm unclear about is you also use getFirstName() and getLastName which are from the User class, but there is no object used to access the User class. I was wondering if declaring that is not required?

Forum.java 
public class Forum {
  private String topic;

  public Forum(String topic)
  {
    this.topic = topic;
  }
  // TODO: add a constructor that accepts a topic and sets the private field topic

  public String getTopic() {
    return topic;
  }


  // Uncomment this when you are prompted to do so
  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;
    this.lastName = lastName;
  }

   public String getFirstName()
   {
     return firstName;
   }

   public String getLastName()
   {
      return lastName;
   }

  // TODO: add getters for firstName and lastName

}
ForumPost.java 
public class ForumPost {
  private User author;
  private String title;
  private String description;

   public ForumPost(User author, String title, String description)
   {
     this.author = author;
     this.title = title;
     this.description = 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;
  }
}
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);
    }
    // Uncomment this when prompted
    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, "WWE", "Gimme a Hell Yeah!");
    forum.addPost(post);

// 
  }

}

3 Answers

Dekel Zoaretz
Dekel Zoaretz
14,864 Points
Dekel Zoaretz
Dekel Zoaretz
14,864 Points

As far as I can see the post.getAuthor() is returning a reference to the user object that is being populated in the ForumPost constructor.

public class ForumPost {
  private User author;
  ...

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

  public User getAuthor() {
    return author;
  }
  ...
}
andren
andren
28,558 Points
andren
andren
28,558 Points

The getAuthor method returns author which contains a User object. When you chain method calls together like is done in this line post.getAuthor().getFirstName() you call the second method on the thing returned by the first method.

So getFirstName() is being called on the User object that the getAuthor() method returns. Which means the methods are in fact being called on a User object. It's just one being returned from a method rather than one defined within the class. Which is a completely valid thing to do.

It's technically no different from doing something like this:

 public void addPost(ForumPost post) {
    User author = post.getAuthor();
    System.out.printf("A new post in %s topic from %s %s about %s is available",
            topic,
            author.getFirstName(),
            author.getLastName(),
            post.getTitle()
    );
  }

They are just skipping out on creating a variable to hold the User object.

Steven Morimoto
Steven Morimoto
Courses Plus Student 1,836 Points
Steven Morimoto
Steven Morimoto
Courses Plus Student 1,836 Points

Thanks! It took me awhile to figure out that author was the object for accessing the User class

Steven Morimoto
PLUS
Steven Morimoto
Courses Plus Student 1,836 Points
Steven Morimoto
Steven Morimoto
Courses Plus Student 1,836 Points

Ok, now I see. Thank you! And I had so much trouble with the User object in the ForumPost class!