./Game.java:13: error: invalid method declaration; return type requir...

./Game.java:13: error: invalid method declaration; return type requir
ed                                                                   
  private validateGuess(char letter) {                               
               ^                                                          
./Game.java:21: error: incompatible types: unexpected return value   
        return letter;                                               
                   ^                                                     
./Game.java:25: error: cannot find symbol                            
    letter = validateGuess(letter);                                  
                 ^                                                       
  symbol:   method validateGuess(char)                               
  location: class Game                                               
./Prompter.java:26: error: cannot find symbol                        
      isHit = mGame.applyGuess(guess);
                                                    ^                                     
  symbol:   variable guess
  location: class Prompter                                         
4 errors 

public class Game {
  public static final int MAX_MISSES = 7;
  private String mAnswer;
  private String mHits;
  private String mMisses;

  public Game(String answer) {
    mAnswer = answer;
    mHits = "";
    mMisses = "";
  }

  private validateGuess(char letter) {
    if (! Character.isLetter(letter)) {
      throw new IllegalArgumentException("A letter is required");
    }
    letter = Character.toLowerCase(letter);
    if (mMisses.indexOf(letter) >= 0 || mHits.indexOf(letter) >= 0) {
      throw new IllegalArgumentException(letter + " has already been guessed");
    }
        return letter;
  }

  public boolean applyGuess(char letter) {
    letter = validateGuess(letter);
    boolean isHit = mAnswer.indexOf(letter) >= 0;
    if (isHit) {
      mHits += letter;
    } else {
      mMisses += letter;
    }
    return isHit;
  }

  public String getCurrentProgress() {
    String progress = "";
    for (char letter: mAnswer.toCharArray()) {
      char display = '-';
      if (mHits.indexOf(letter) >= 0) {
        display = letter;
      }
      progress += display;
    }
    return progress;
  }
  public int getRemainingTries() {
  return MAX_MISSES - mMisses.length(); 
  }

  }

public class Hangman {

    public static void main(String[] args) {
        // Enter amazing code here:
      Game game = new Game("treehouse");
      Prompter prompter = new Prompter(game);
      prompter.play();
    }

}

import java.io.Console;

public class Prompter {
  private Game mGame;

  public Prompter(Game game) {
    mGame = game;
  }

  public void play() {
    while(mGame.getRemainingTries() > 0) {
      displayProgress();
      promptForGuess();
    }
  }

  public boolean promptForGuess() {
    Console console = System.console();
    boolean isHit = false;
    boolean isValidGuess = false;
    while (! isValidGuess) {
    String guessAsString = console.readLine("Enter a letter:  ");
    char guess = guessAsString.charAt(0);
    }
    try {
      isHit = mGame.applyGuess(guess);
      isValidGuess = true;

    } catch (IllegalArgumentException iae) {
      console.printf("%s. Please try again.", iae.getMessage());
    }
    return isHit;
  }

  public void displayProgress() {
    System.out.printf("You have %d tries left to solve:  %s\n",
                      mGame.getRemainingTries(),
                      mGame.getCurrentProgress());
  }

}