Is my regular expression wrong?

Question

Hi,
I have a string (5+4-6*7/8) which I need to separate into
Digits and Operators.I am using regular expressions for this.
Here's my code.
String s = "(5+4-6*7/8)";
String delim = "(/+-*)";
Pattern Digit = Pattern.compile("[0-9]");
// Create a regular expression which will match only digits.
Pattern LeftParen = Pattern.compile("[(]");
// Create a regular expression which will match only Left Parenthesis.
Matcher m; //Create a Matcher instance
StringTokenizer st = new StringTokenizer(s,delim,true);
n = st.countTokens();
while (st.hasMoreTokens())
t = st.nextToken();
// Match the string token t with the Digit Pattern.
m = Digit.matcher(t);
if(m.matches())
// if condition is true,then its a digit.Hence push it on number stack "sn".
sn.push(t);
m.reset();
m = LeftParen.matcher(t);
// Match the string token t with the Left Parenthesis Pattern.
if(m.matches())
// If condition is true,then its a left parenthesis.Hence push it on operator stack "so".
so.push(t);
prec=0;
new_prec=0;
}//End of while loop
After this my number stack "sn" is having only digit values,which is fine.
But my operator stack "so" does not contain any elements viz (.+,-,*,/,).
What's wrong in my code?
Thanks,
-Prashant.

Answer 1

First of all, unless you only ever plan on having single digit numbers in your program, the RE for numbers is wrong. I believe that it should be [0-9]*
Secondly, brackets are used for groupings, e.g. [a-z][0-9] so you don't need them for your open parenthesis. Third, since parenthesis are operators in RE, you probably want to escape your parenthesis:
Pattern LeftParen = Pattern.compile("\(")