Problem Evaluate Reverse Polish Notation

Problem Description: 

Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Valid operators are +, -, *, /. Each operand may be an integer or another expression.

Solution:

public int evalRPN(String[] tokens) {
        Stack<String> operands = new Stack<String>();
        for (int i = 0; i < tokens.length; i++) {
            if (!(tokens[i].equals("+") || tokens[i].equals("-") || tokens[i].equals("*") || tokens[i].equals("/"))) {
                operands.push(tokens[i]);
            } else {
                String opRight = operands.pop();
                String opLeft = operands.pop();
                String result = "";
                if (tokens[i].equals("+")) {
                    result = String.valueOf(Integer.valueOf(opLeft) + Integer.valueOf(opRight));
                } else if (tokens[i].equals("-")) {
                    result = String.valueOf(Integer.valueOf(opLeft) - Integer.valueOf(opRight));
                } else if (tokens[i].equals("*")) {
                    result = String.valueOf(Integer.valueOf(opLeft) * Integer.valueOf(opRight));
                } else if (tokens[i].equals("/")) {
                    result = String.valueOf(Integer.valueOf(opLeft) / Integer.valueOf(opRight));
                }    
                operands.push(result);
            }
        }

        return Integer.valueOf(operands.pop());
    }