Problem Evaluate Reverse Polish Notation

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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:

 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     }