Lists & Iterators

3. As another example of iterator on a "virtual" collection, StringTokenizer can be used to get the list of words into a string:

StringTokenizer tok = new StringTokenizer("I love Java."," .");
while (tok.hasMoreTokens())
  System.out.println( tok.nextToken() ); // ["I","love","Java"]

As an application, the next code implements a simple calculator:

public static void main(String[] args) {
  Stack<Integer> stack = new Stack<Integer>();
  StringTokenizer tok  = new StringTokenizer("1 2 + 3 *");
  int v1,v2;
  while(tok.hasMoreTokens()) {
    String val = tok.nextToken();
    switch (val) {
      case "+": 
        v1 = stack.pop();
        v2 = stack.pop();
        stack.push(v1+v2);
        break;
      case "*": 
        v1 = stack.pop();
        v2 = stack.pop();
        stack.push(v1*v2);
        break;
      default: stack.push(Integer.parseInt(val));
    }
  }
  System.out.println(stack);
}

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