Welcome to the Treehouse Community

The Treehouse Community is a meeting place for developers, designers, and programmers of all backgrounds and skill levels to get support. Collaborate here on code errors or bugs that you need feedback on, or asking for an extra set of eyes on your latest project. Join thousands of Treehouse students and alumni in the community today. (Note: Only Treehouse students can comment or ask questions, but non-students are welcome to browse our conversations.)

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and a supportive community. Start your free trial today.

Java Java Objects Creating the MVP Current Progress

NullPointerException

I've followed what they did in the video step by step and I keep getting a NullPointerException when I run Hangman.java.

It says it's at Game.getCurrentProgress, Prompter.displayProgress, and Hangman.main.

I've looked up the null pointer exception and found that it's something along the lines of a null value being where a value should be, but I don't understand why that's happening. I've looked at this code until I'm cross eyed and can't figure out what's going wrong.

game.java:

class Game { private String answer; private String hits; private String misses;

public Game (String answer) { this.answer = answer;

}

public boolean applyGuess(char letter) { boolean isHit = answer.indexOf(letter) != -1; if(isHit) { hits += letter; } else { misses += letter; } return isHit; } public String getCurrentProgress() { String progress = ""; for (char letter : answer.toCharArray()) { char display = '-'; if (hits.indexOf(letter) != -1) { display = letter; } progress += display; } return progress; } }

prompter.java :

import java.util.Scanner;

class Prompter { private Game game;

public Prompter(Game game) { this.game = game; }

public boolean promptForGuess() { Scanner scanner = new Scanner(System.in); System.out.print("Enter a letter: "); String guessInput = scanner.nextLine(); char guess = guessInput.charAt(0); return game.applyGuess(guess); }

public void displayProgress() { System.out.printf("Try to solve : %s%n" , game.getCurrentProgress()); } }

2 Answers

Evan Cook ,

you need to initialize the variables "Hits" and "Misses" in the constructor like he did. After that you shouldn't anymore get the NullPointerException.

Example:

  private String answer;
  private String hits;
  private String misses;

  public Game(String answer) {
    this.answer = answer;
    this.hits = ""; // you need this
    this.misses = ""; // you need this
  }
Moira Lawrie-Martyn
Moira Lawrie-Martyn
7,819 Points

Can you post the exact error? As it usually tells you the line where the problem is which helps you pin down the problem

Sure.

Exception in thread "main" java.lang.NullPointerException at Game.getCurrentProgress(Game.java:24) at Prompter.displayProgress(Prompter.java:20) at Hangman.main(Hangman.java:8)