I tried.. but...

Hi Jinhwa,

Let's do this one at a time ... Q1: In the Forum class, add a constructor that takes a String for the topic and sets the private field mTopic.

So, we need to create a constructor. That's a method that returns nothing (and not a void return either) and is called the same name as the class, Forum. This one takes one string and sets the mTopic variable inside it:

  public Forum(String topic){
    mTopic = topic;
  }

Next, in the User class: Q2 Can you please add the private fields to store the parameters defined in the constructor? Ooh while you're at it can you add the appropriate getters?

That's quite a lot of typing!! Three jobs: 1. add the member variables based on what the constructor receives, 2. set those member variables inside the constructor and 3. create the getter methods:

public class User {
  private String mFirstName; // 1. added member variables here
  private String mLastName;

  public User(String firstName, String lastName) {
    // TODO:  Set the private fields here
    mFirstName = firstName; // 2. set them in here
    mLastName = lastName;
  }
  // 3. add the getters below
  public String getFirstName(){
    return mFirstName;
  }

  public String getLastName(){
    return mLastName;
  }
}

That's a lot of code - read through it and make sure it is familiar - I've commented the three tasks to highlight them. I'll post the next bits on a separate answer as this one is getting long!!

Steve.

Right - on to task 3 ... It's going to need a constructor that takes a User author a String title and a String description. Don't forget to initialize the member fields in the constructor. Also please add the getter for mDescription.

We're in the ForumPost class now. We need to create a constructor and set the three member variables inside it. Then add a getter for one of them:

// here's the constructor
  public ForumPost(User author, String title, String description){
    mAuthor = author;
    mTitle = title;
    mDescription = description;
  }
  // here's the getter
  public String getDescription(){
    return mDescription;
  }

The next bit is a little long too! First, uncomment the line in Forum:

  public void addPost(ForumPost post) {
      /* When all is ready uncomment this... */
      System.out.printf("New post from %s %s about %s.\n",
                         post.getAuthor().getFirstName(),
                         post.getAuthor().getLastName(),
                         post.getTitle());

  }

Then switch to Example where there's a load of commented out code. Uncomment these one at a time (not he actual comments, just the code lines!:

    // Forum forum = new Forum("Java");
    // Take the first two elements passed args
    // User author = new User();
    // Add the author, title and description
    // ForumPost post = new ForumPost();
    // forum.addPost(post);

I'll start a new answer again ...

why do you write " forum.addpost(post); ??????/

and also what is the purpose of "Example.java" ????

Hi there,

There's a few objects here that are all brought together. Example.java does that, it holds the main function which drives the execution of the application.

Let's take the last code block in Example, and read through the comments too:

    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, "A Title", "A Description");
    forum.addPost(post);

First, we create an instance of a Forum, called forum. Then we do the same for a User object and a ForumPost object too.

The last line, forum.addPost(post); adds the instance of the ForumPost object, called post into the instance of a Forum object, called forum. The addPost method defined in the Forum class manages this and takes a post as a parameter.

I hope that explains a little more for you.

Steve.