[Leetcode] Evaluate Reverse Polish Notation

Evaluate the value of an arithmetic expression in Reverse Polish Notation.
Valid operators are +, -, *, /. Each operand may be an integer or another expression.
Some examples:

  ["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9
  ["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6

Use stack to hold the numbers and whenever meet a operator, we pop the top two number and calculate the result then push the result back to the stack. The final result would be remained in the stack.

    public int evalRPN(String[] tokens) {
        int n = tokens.length;
        if(n == 0)
            return 0;
        Stack<Integer> nums = new Stack<Integer>();
        for(int i = 0; i < n; i++) {
            if(tokens[i].equals("+")) {
                int num2 = nums.pop();
                int num1 = nums.pop();
                nums.push(num1 + num2);
            }
            else if(tokens[i].equals("-")) {
                int num2 = nums.pop();
                int num1 = nums.pop();
                nums.push(num1 - num2);
            }
            else if(tokens[i].equals("*")) {
                int num2 = nums.pop();
                int num1 = nums.pop();
                nums.push(num1 * num2);
            }
            else if(tokens[i].equals("/")) {
                int num2 = nums.pop();
                int num1 = nums.pop();
                nums.push(num1 / num2);
            }
            else {
                nums.push(Integer.parseInt(tokens[i]));
            }
        }
        return nums.pop();
    }