Problem Evaluate Reverse Polish Notation

 1 public int evalRPN(String[] tokens) {
 2         Stack<String> operands = new Stack<String>();
 3         for (int i = 0; i < tokens.length; i++) {
 4             if (!(tokens[i].equals("+") || tokens[i].equals("-") || tokens[i].equals("*") || tokens[i].equals("/"))) {
 5                 operands.push(tokens[i]);
 6             } else {
 7                 String opRight = operands.pop();
 8                 String opLeft = operands.pop();
 9                 String result = "";
10                 if (tokens[i].equals("+")) {
11                     result = String.valueOf(Integer.valueOf(opLeft) + Integer.valueOf(opRight));
12                 } else if (tokens[i].equals("-")) {
13                     result = String.valueOf(Integer.valueOf(opLeft) - Integer.valueOf(opRight));
14                 } else if (tokens[i].equals("*")) {
15                     result = String.valueOf(Integer.valueOf(opLeft) * Integer.valueOf(opRight));
16                 } else if (tokens[i].equals("/")) {
17                     result = String.valueOf(Integer.valueOf(opLeft) / Integer.valueOf(opRight));
18                 }    
19                 operands.push(result);
20             }
21         }
22 
23         return Integer.valueOf(operands.pop());
24     }