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Java Java Objects Delivering the MVP Forum

Getting an error that arguments passed in from the main method in Main.java is null. Why ?

When I pass args[0] and args[1] in "Forum forum = new Forum (args[0] , args[1]);", it shows an error that the args[0], args[1] are still null occupied. Can anyone help me out

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;
  }


  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 {
  private String firstName,lastName;
  // TODO: add private fields for firstName and lastName

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

  }

  // TODO: add getters for firstName and 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");
    // 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,"Time Waste","Is Injurious");
    forum.addPost(post);

// */
  }

}

1 Answer

Umesh Ravji
Umesh Ravji
42,386 Points

Hi Karthik, the problem is with the User class constructor. The values of firstName and lastName need to be set here to what is passed in. If you follow what your code is actually doing, you should be able to see why they are both set to NULL when you create a User object.

public User(String firstName, String lastName) {
  this.firstName = firstName;
  this.lastName = lastName;
}