private static Boolean nextOpIs(String str, String op){
        String currentSub;
        for(int i = 0; i < str.length(); i++){
            currentSub = str.substring(i,i+1);
            if(currentSub.equals("-") || currentSub.equals("+") || currentSub.equals("*") || currentSub.equals("/")){
                if(currentSub.equals(op)){
                    //System.out.println("nextopis match"); used for testing
                    return true;
                }
                else
                    break;
            }
        }
        return false;
    }