Using Java’s recursive expression evaluator

I want to write an expression evaluator that only does addition and subtraction I have a simple algorithm to do this; However, I have some implementation problems

I think an expression (it's a string) @ h_ 301_ 3@

"(" <expression1> <operator> <expression2> ")"

This is my algorithm @ H_ 301_ 3@

String evaluate( String expression )

   if expression is digit
      return expression

   else if expression is "(" <expression1> <operator> <expression2> ")"
      cut the brackets out of it
      expression1 = evaluate( <expression1> )
      operator = <operator>
      expression2 = evaluate( <expression2> )

   if operator is +
      expression1 + expression2

   else if operator is -
      expression1 - expression2

My problem is to parse < expression1 > < operator > and < expression2 > from expression How can I do this@ H_ 301_ 3@

Note: I'm not asking for a code All I need is an idea@ H_ 301_ 3@

Thank you, @ h_ 301_ 3@

- Ali@H_301_3 @

Solution

Don't do this, then:) when you see an opening bracket, your recursive call expression At the end of the expression, either find another operator (so you're not at the end of the expression at all) or a closing parenthesis, in which case you'll return from the evaluation@ H_ 301_ 3@