RPN - Reverse Polish Notation calculator

ReversePolishCalculator.java

import java.util.*;

class ReversePolishCalculator {

    interface Operation {
        int calculate(int a, int b);
    }

    enum MathOperation implements Operation {
        ADD('+') {
            @Override
            public int calculate(int a, int b) {
                return a + b;
            }
        },
        SUB('-') {
            @Override
            public int calculate(int a, int b) {
                return a - b;
            }
        },
        MUL('*') {
            @Override
            public int calculate(int a, int b) {
                return a * b;
            }
        },            
        DIV('/') {
            @Override
            public int calculate(int a, int b) {
                return a / b;
            }
        };

        private final char op;
        private MathOperation(char c) {
            this.op = c;
        }
        
        public static MathOperation getByOp(final char op) {
            for (final MathOperation math : values() ) {
                if (math.op == op) return math;
            }
            return null;
        }
    }
    
    final static List<String> OPS = Arrays.asList("+", "-", "*", "/");



    public static void main(String ... args) {
        System.out.println(calculate("2 1 - 8 +")); // 9
        System.out.println(calculate("5 1 2 + 4 * + 3 -")); // 14

    }
    
    private static int calculate(final String input) {
        final String[] elements = input.split(" ");
        final Stack<Integer> stack = new Stack<>();
        for (int index = 0; index < elements.length; index++ ) {
            final String current = elements[index];
            if ( OPS.contains(current) ) {
                // calc
                final int right = stack.pop();
                final int left = stack.pop();
                final MathOperation math = MathOperation.getByOp(current.charAt(0)); 
                final int result = math.calculate(left, right);
                stack.push(result);
            } else {
                stack.push(Integer.valueOf(current));
            }
        }
        return stack.pop();
    }
}