private void stepMonth() {
    if(fIsPlus){
      fMonth = fMonth + 1;
    }
    else {
      fMonth = fMonth - 1;
    }
    if(fMonth > 12) { 
      fMonth = 1;
      stepYear();
    }
    else if(fMonth < 1){
      fMonth = 12;
      stepYear();
    }
  }