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Java Java Objects (Retired) Delivering the MVP Wrapping up

Niyamat Almass
Niyamat Almass
8,176 Points

i have a problem

i solve the challenge but there are some error in my example.java please solve the problem?

ForumPost.java
public class ForumPost {
  private User mAuthor;
  private String mTitle;
  private String mDescription;

  public User getAuthor() {
    return mAuthor;
  }

  public String getTitle() {
    return mTitle;
  }

  public String getDescription() {
    return mDescription;
  }

  public ForumPost(User author, String title, String description) {

  }
}
User.java
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;
  }

}
Forum.java
public class Forum {
  private String mTopic;

  public String getTopic() {
      return mTopic;
  }

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

  public void addPost(ForumPost post) {

      System.out.printf("New post from %s %s about %s.\n",
                         post.getAuthor().getFirstName(),
                         post.getAuthor().getLastName(),
                         post.getTitle());

  }
}
Example.java
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");
    User author = new User("user", "scheu");
    ForumPost post = new ForumPost(User, "Bomb", "boom!");
    forum.addPost(post);
  }
}

3 Answers

Ken Alger
STAFF
Ken Alger
Treehouse Teacher

Niyamat;

  1. Replace the old author object with your name hard coded with the one that takes args[0] and args[1].
  2. Now that you have an author object put that in when you create your ForumPost object. Currently you are using niyamat which is an undefined variable or object. Replace that with author.

Ken

Niyamat Almass
Niyamat Almass
8,176 Points

Hey Ken Alger i got it!!!!!!!!!!!!!!!! .Thank you so much for your help.

Ken Alger
Ken Alger
Treehouse Teacher

Niyamat;

Pleased that it worked out. This was a tough challenge with getting all of the various classes to interact with one another. Great job in sticking with it and getting it resolved.

Happy coding,

Ken

Ken Alger
STAFF
Ken Alger
Treehouse Teacher

Niyamat;

The error you are having is in the User author = new User("user", "scheu"); line of code. The challenge is wanting to be able to utilize a name passed into it as described in the prompting code

System.out.println("first and last name are required. eg: java Example Craig Dennis");

When you create the new User object, author you want to be able to pass into it the names given. So, in my case to run the program from the command line, I would type in java Example Ken Alger and the Ken and Alger would get passed into the author object for the firstName and lastName values. Make sense?

Post back if you are still stuck.

Ken

Niyamat Almass
Niyamat Almass
8,176 Points

I have still error message .my example.java is

Example.java
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");
    User author = new User("Niyamat", "Almass");

    ForumPost post = new ForumPost(Niyamat, "Bomb", "boom!");
    forum.addPost(post);
  }
}

my error is

output.html
./Example.java:12: error: cannot find symbol
    ForumPost post = new ForumPost(Niyamat, "Bomb", "boom!");
                                   ^
  symbol:   variable Niyamat
  location: class Example
1 error

How to solve the error.What is the exactly code?

Ken Alger
STAFF
Ken Alger
Treehouse Teacher

Niyamat;

That is a step in the right direction, but obviously not quite it, there are still a couple of issues.

Let's take another look at the User object author you have created. As I stated before, you want to be able to pass in a first and last name from the command line at run time. So if I type in the java Example Ken Alger command, the User object author will take the arguments Ken and Alger. Similarly if you were to type in java Example Niyamat Almass we need author to take Niyamat and Almass. This should happen without having to alter the code.

How can we accomplish this? If you look at the main() method for the Example class you will notice that it takes a String [] args as it's argument. What the heck does that mean? It means that it accepts an array (denoted by the square brackets) of arguments as a variable args. This concept is touched on in the Hangman game in the course in which we do java Hangman someWordToSolve and that game examines args[0]. We need to do a similar thing here with this challenge.

Our User object needs to be able to accept two arguments, args[0] and args[1]. This will "grab" the first two arguments after our java Example statement in the command line. Since the constructor for the User class accepts two arguments (first name and last name) we should be able to pass in the command line arguments into our model. We can do that during the creation of our User object with

// set the firstName and lastName to the name passed in from the command line
User author = new User(args[0], args[1]); 

The other issue you have in the above code is for the creation of your ForumPost object. If you take a look at the constructor for that class, it should be set up as ForumPost(User author, String title, String description). Since we just discussed the creation of a User object we should just pass in the author object during the creation of our ForumPost object.

Post back with additional questions or if you are still stuck.

Happy coding,

Ken

Niyamat Almass
Niyamat Almass
8,176 Points

hey Ken Alger thank you.but i still don't get it.where i put the argument method (User author = new User(args[0], args[1]);)

Example.java
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"); 
    User author = new User(args[0], args[1]);
    User author = new User("Niyamat", "Almass");
    ForumPost post = new ForumPost(niyamat, "Bomb", "boom!");
    forum.addPost(post);
  }
}

There is some error

output.html
./Example.java:11: error: variable author is already defined in method main(String[])
    User author = new User("Niyamat", "Almass");
         ^
./Example.java:12: error: cannot find symbol
    ForumPost post = new ForumPost(niyamat, "Bomb", "boom!");
                                   ^
  symbol:   variable niyamat
  location: class Example
2 error

And please tell me the right code about this

Example.java
  User author = new User("Niyamat", "Almass");
    ForumPost post = new ForumPost(niyamat, "Bomb", "boom!");