public class EvaluateExpression {
  public static void main(String[] args) {
    // Check number of arguments passed
    if (args.length < 1) {
      System.out.println(
        "Usage: java EvaluateExpression expression");
      System.exit(0);
    }

    String expression = "";
    for (int i = 0; i < args.length; i++)
      expression += args[i];

    try {
      System.out.println(evaluateExpression(expression));
    }
    catch (Exception ex) {
      System.out.println("Wrong expression");
    }
  }

  /** Evaluate an expression */
  public static int evaluateExpression(String expression) {
    // Create operandStack to store operands
    GenericStack<Integer> operandStack 
      = new GenericStack<Integer>();
  
    // Create operatorStack to store operators
    GenericStack<Character> operatorStack 
      = new GenericStack<Character>();
  
    // Extract operands and operators
    java.util.StringTokenizer tokens =
      new java.util.StringTokenizer(expression, "()+-/*", true);
 
    // Phase 1: Scan tokens
    while (tokens.hasMoreTokens()) {
      String token = tokens.nextToken().trim(); // Extract a token
      if (token.length() == 0) // Blank space
        continue; // Back to the while loop to extract the next token
      else if (token.charAt(0) == '+' || token.charAt(0) == '-') {
        // Process all +, -, *, / in the top of the operator stack 
        while (!operatorStack.isEmpty() &&
          (operatorStack.peek() == '+' ||
           operatorStack.peek() == '-' ||
           operatorStack.peek() == '*' ||
           operatorStack.peek() == '/')) {
          processAnOperator(operandStack, operatorStack);
        }

        // Push the + or - operator into the operator stack
        operatorStack.push(token.charAt(0));
      }
      else if (token.charAt(0) == '*' || token.charAt(0) == '/') {
        // Process all *, / in the top of the operator stack 
        while (!operatorStack.isEmpty() &&
          (operatorStack.peek() == '*' ||
          operatorStack.peek() == '/')) {
          processAnOperator(operandStack, operatorStack);
        }

        // Push the * or / operator into the operator stack
        operatorStack.push(token.charAt(0));
      }
      else if (token.trim().charAt(0) == '(') {
        operatorStack.push('('); // Push '(' to stack
      }
      else if (token.trim().charAt(0) == ')') {
        // Process all the operators in the stack until seeing '('
        while (operatorStack.peek() != '(') {
          processAnOperator(operandStack, operatorStack);
        }
        
        operatorStack.pop(); // Pop the '(' symbol from the stack
      }
      else { // An operand scanned
        // Push an operand to the stack
        operandStack.push(new Integer(token));
      }
    }

    // Phase 2: process all the remaining operators in the stack 
    while (!operatorStack.isEmpty()) {
      processAnOperator(operandStack, operatorStack);
    }

    // Return the result
    return operandStack.pop();
  }

  /** Process one operator: Take an operator from operatorStack and
   *  apply it on the operands in the operandStack */
  public static void processAnOperator(
      GenericStack<Integer> operandStack, 
      GenericStack<Character> operatorStack) {
    char op = operatorStack.pop();
    int op1 = operandStack.pop();
    int op2 = operandStack.pop();
    if (op == '+') 
      operandStack.push(op2 + op1);
    else if (op == '-') 
      operandStack.push(op2 - op1);
    else if (op == '*') 
      operandStack.push(op2 * op1);
    else if (op == '/') 
      operandStack.push(op2 / op1);
  }
}