Problem with infix evaluator?

I don't know if the evaluator actually works correctly because it always returns a result of zero. I have been messing with it for a while and can't seem to figure out why it won't give any other value than zero for the result. Thanks ahead of time for the help.

Code:

---

import java.util.Scanner;

public class InFixEvaluator
{
  public static int evaluate(String expression)
  {
    BoundedStackInterface<String>  opStack    = new ArrayStack<String>(50); 
    BoundedStackInterface<Integer> valueStack = new ArrayStack<Integer>(50);
   
    String thisOp;
    int value;
    int operand1;
    int operand2;

    int result = 0;

    Scanner tokenizer = new Scanner(expression);

    while (tokenizer.hasNext()){
      if (tokenizer.hasNextInt())
      {
        value = tokenizer.nextInt();
        valueStack.push(value);
      }
      else{
        thisOp = tokenizer.next();
              opStack.push(thisOp);
      }
    }
    while(!opStack.isEmpty()){
            thisOp = opStack.top();
            opStack.pop();
      if (thisOp == ")")
        while(thisOp != "("){
                operand1 = valueStack.top();
                valueStack.pop();
                operand2 = valueStack.top();
                valueStack.pop();
                thisOp = opStack.top();
                opStack.pop();
        // Perform operation.
        if(thisOp.equals("*")){
          result = operand1 * operand2;
        valueStack.push(result);
        }
        else
        if(thisOp.equals("+")){
          result = operand1 + operand2;
          valueStack.push(result);
        }
        else
        if(thisOp.equals("-")){
          result = operand1 - operand2;
          valueStack.push(result);
        }
        else
                System.out.println("Invalid Operator");
      }
      if(opStack.isEmpty())
              break;
      else {
        operand1 = valueStack.top();
        valueStack.pop();
        operand2 = valueStack.top();
        valueStack.top();
        thisOp = opStack.top();
        opStack.pop();
      if(thisOp.equals("*"))
                result = operand1 * operand2;
      else
      if(thisOp.equals("+"))
                result = operand1 + operand2;
      else
      if(thisOp.equals("-"))
            result = operand1 = operand2;
      else
              System.out.println("Invalid operator");
      valueStack.push(result);
        }
      result = valueStack.top();
    }
    return result;
  }
}

---

That is the evaluator and here is the code main class.

Code:

---

import java.util.Scanner;

public class IFixConsole {

        public static void main(String[] args) {
                Scanner input = new Scanner(System.in);
               
                String line;
                String more;
               
                int result;
               
                do{
                        System.out.println("Enter a infix expression to be evaluated: ");
                        line = input.nextLine();
                        result = InFixEvaluator.evaluate(line);
                        System.out.println();
                        System.out.println("Result = " + result);
                        System.out.println();
                        System.out.println("Evaluate another expression? (Y = Yes): ");
                        more = input.nextLine();
                        System.out.println();
                }
                while (more.equalsIgnoreCase("y"));
               
                System.out.println("Program completed.");
        }
}

---

There's a lot going on in that evaluate() method. Sprinkle in some System.out.println( ... ) statements and print the current stack top, operators and operands so you can see what's actually happening in there.

kind regards,

Jos

Thanks I didn't even think about trying that.

Code:

---

import java.util.Scanner;

public class InFixEvaluator
{
  public static int evaluate(String expression)
  {
    BoundedStackInterface<String>  opStack    = new ArrayStack<String>(50); 
    BoundedStackInterface<Integer> valueStack = new ArrayStack<Integer>(50);
   
    String thisOp;
    int value;
    int operand1;
    int operand2;

    int result = 0;

    Scanner tokenizer = new Scanner(expression);

    while (tokenizer.hasNext()){
      if (tokenizer.hasNextInt()){
        value = tokenizer.nextInt();
        valueStack.push(value);
      }
      else{
        thisOp = tokenizer.next();
        opStack.push(thisOp);
      }
    }
    while(!opStack.isEmpty()){
        thisOp = opStack.top();
        opStack.pop();
      if (thisOp == ")"){
        while(thisOp != "("){
            operand1 = valueStack.top();
            valueStack.pop();
            System.out.println(operand1);
            operand2 = valueStack.top();
            valueStack.pop();
            System.out.println(operand2);
            thisOp = opStack.top();
            opStack.pop();
            System.out.println(thisOp);
           
        if(thisOp.equals("*")){
          result = operand1 * operand2;
        valueStack.push(result);
        }
        else
        if(thisOp.equals("+")){
          result = operand1 + operand2;
          valueStack.push(result);
        }
        else
        if(thisOp.equals("-")){
          result = operand1 - operand2;
          valueStack.push(result);
        }
      }
      }
      else {
        operand2 = valueStack.top();
        valueStack.pop();
        operand1 = valueStack.top();
        valueStack.pop();
      if(thisOp.equals("*"))
            result = operand1 * operand2;
      else
      if(thisOp.equals("+"))
            result = operand1 + operand2;
      else
      if(thisOp.equals("-"))
            result = operand1 - operand2;
     
      valueStack.push(result);
      }
      result = valueStack.top();
    }
    return result;
  }
}

---

That is what I have so far and it works when there is no parentheses. I need it to work with parentheses and I need the operators to work in the correct precedence which I am having trouble figuring out how to do that.