Creating an Infix Calculator using Stacks

Question

Hi, I am writing code that parses an infix expression input from the user (seperated by white spaces).
I have to use stacklist class. using stringtokenizer to parse the expression.
have to ignore left paren, push operators into opStack push operands into numStack and when right paren occurs pop numbers and combine with operator at top of stack.
I have created this code,but for some reason it gives me the error "
InfixCalulator2.java:30: cannot find symbol
symbol : method push(java.lang.String)
location: class java.util.ArrayList
opStack.push(sx); "
Am i using the push an pop Stack method correctly??
Thanks!!
    class InfixCalulator2{
       private static void main(String[] args){
         String inputline = "(1 + 3)";
         ArrayList opStack = new ArrayList();
         ArrayList numStack = new ArrayList();
               int parenCount = 0;
           StringTokenizer st = new StringTokenizer(inputline, " ", false);
         String sx = st.nextToken();
         while (st.hasMoreTokens()) {
            sx = st.nextToken();
            if (sx.equals("(")) {
               parenCount++;
            else if ( (sx.equals("+")) || (sx.equals("-"))
               || (sx.equals("*")) || (sx.equals("/")) ) {
               opStack.push(sx); //here is where it starts givign me error for push, same with pop
            else if (sx.equals(")")) {
               parenCount--;
               double num2 = ((Double)numStack.pop()).doubleValue();
               double num1 = ((Double)numStack.pop()).doubleValue();
               String op = (String)opStack.pop();
               double result = 0.0d;
               if (op.equals("+")) {
                  result = num1 + num2;
               else if (op.equals("-")) {
                  result = num1 - num2;
               else if (op.equals("*")) {
                  result = num1 * num2;
               else if (op.equals("/")) {
                  result = num1 / num2;
               numStack.push(new Double(result));
            System.out.println("Result of computation: " + ((Double)numStack.pop()).doubleValue());
   }

Answer 1

By the way, youll really learn a lot if you take
pragmatic steps to
solving your problems. One example would be actually
reading
your error messages (theres a reason they dont just
read "BROKEN!").
InfixCalulator2.java:30: cannot find symbol
symbol : method push(java.lang.String)
location: class java.util.ArrayListThat error message is saying CAN NOT FIND SYMBOL
METHOD
"PUSH()" IN ARRAYLIST.
Notice how ArrayList does NOT have a push() or pop()
method
but the List implementation Stack does:
http://java.sun.com/j2se/1.4.2/docs/api/java/util/Stac
k.htmlthanks, stupid mistake....