Problem with referencing nodes

Question

Hey I am having an odd problem writing a program that uses a Stack to build an expression tree. I have the Stack class set up and my main so that I can locate operators and make a new Node with the operator and put it on the top of the stack, and do the same with the operands. However when I go to push the operator Node (i.e. assign the topOfStack field in my LLStack class to the node I pass) it loses the character in the operator field of my Node. Any idea as to why this happens? I can build the operand stack fine. Here are my classes:
public class LLStack {
          private IntSLLNode topOfStack;
          public LLStack(){
               topOfStack=null;
          public boolean isEmpty(){
               return topOfStack==null;
          public void push(IntSLLNode el){
               topOfStack= new IntSLLNode(el, topOfStack);
          public IntSLLNode pop(){
               if(isEmpty())
                    return null;
               else
                    IntSLLNode top=topOfStack;
                    topOfStack=topOfStack.next;
                    return top;
}main method
                        Scanner scanString = new Scanner(System.in);
          System.out.println("Enter a postfix expression: ");
          String inputString= scanString.nextLine();
                        LLStack operatorStack = new LLStack();   //create new stacks
               LLStack treeStack = new LLStack();
               for(int i=0;i<inputString.length();i++){
                    if(inputString.charAt(i)=='+'|inputString.charAt(i)=='*'|inputString.charAt(i)=='-'){
                         IntSLLNode optr= new IntSLLNode(inputString.charAt(i));
                         operatorStack.push(optr);          
                    else
                         IntSLLNode opnd= new IntSLLNode(Integer.parseInt(Character.toString(inputString.charAt(i))));
                         treeStack.push(opnd);
                    }In other words...when I apply this line
topOfStack= new IntSLLNode(el, topOfStack);The data in the operator field in "el" does not get assigned to the same field in topOfStack. In Eclipse it shows it as blank. Any ideas why?

Answer 1

oaklandathletic wrote:
Fixed it.Funny how explaining a problem for others helps you to work out the solution yourself, isn't it?
Don't forget that if you decide on programming as a career.
Winston