Infix Calculator (i/o problems)

Question

Greets all. My assignment is to write a program which evaluates an infix expression. I have no problem with this part, but how do I read the user input and know what each character is? I have this so far:
StringTokenizer tokenizer = new StringTokenizer(the_expression);
while (tokenizer.hasMoreTokens())
String token = tokenizer.nextToken(); // the token to examine
double number = 0.0; // the number to push
char an_operator; // the operator to push
// if the first character is a digit, the whole thing must be
if (Character.isDigit(token.charAt(0)))
number = Double.parseDouble(token);
System.out.println(number);
else if (token.charAt(0) == RIGHT_PAREN)
System.out.println("there was a paren.");
else
an_operator = token.charAt(0);
System.out.println(an_operator + " is an operator.");
I don't know what the hell I'm doing. Maybe someone has a better way of reading the input and pushing numbers into a number stack and operators into an operators stack. TIA.

Answer 1

Try using a StringBuffer instead of the Tokenizer. The tokenizer is used to seperate text from a special character in a string.
You actually want to parse through the entire thing.
read about stringbuffer in the java api reference