Hangman exercise error - cannot find symbol

I'm getting this error: ./Game.java:26: error: cannot find symbol
if (hits.indexof(letter) != -1) {
^
symbol: method indexof(char)
location: variable hits of type String
1 error

Here is the code...

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

public Game(String answer) { this.answer = answer; hits = ""; misses = ""; }

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; }

}