I keep getting strange errors

Hello. I really need your help on this one. I used to get 9 errors but I managed to clear most . I checked the code with the tutorial, searched in Google but the errors returned just don't make sense. I'm stuck with this:

./Game.java:18: error: bad operand types for binary operator '||'
if (mMisses.indexOf(letter) >= 0 || mHits.indexOf(letter)) >=0) {
^
first type: boolean
second type: int
./Game.java:25: error: cannot find symbol
letter = validateLetter(letter);
^
symbol: method validateLetter(char)
location: class Game
4 errors

Here is my Game.java.com:

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 char 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 = validateLetter(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(); } }