private String runAnOperation(int i, int j){
        Double a=Double.parseDouble(calculatorSequence.get(i));
        String s=calculatorSequence.get(i+1);
        Double b=Double.parseDouble(calculatorSequence.get(j));
        double z=0;
        if (s.equals("+"))
            z= Add(a,b);
        if (s.equals("-"))
            z= Subtract(a,b);
        if (s.equals("*"))
            z= Multiply(a,b);
        if (s.equals("/"))
            z= Divide(a,b);
        return getDouble(z);
}