playNote, stopNote and isNotePlaying implementations for the Piano tutorial

PianoView.java

public void playNote(int note) {
  if (!isNotePlaying(note)) {
    PlayThread thread = new PlayThread(note);
    thread.start();
    threadMap.put(note, thread);
  }
}

public void stopNote(int note) {
  PlayThread thread = threadMap.get(note);

  if (thread != null) {
    threadMap.remove(note);
  }
}

public boolean isNotePlaying(int note) {
  return threadMap.get(note) != null;
}