Project Euler, problem 8

scratch_7.java

import java.math.BigInteger;

class Scratch {
    private static String NUMBER = "73167176531330624919225119674426574742355349194934" +
            "96983520312774506326239578318016984801869478851843" +
            "85861560789112949495459501737958331952853208805511" +
            "12540698747158523863050715693290963295227443043557" +
            "66896648950445244523161731856403098711121722383113" +
            "62229893423380308135336276614282806444486645238749" +
            "30358907296290491560440772390713810515859307960866" +
            "70172427121883998797908792274921901699720888093776" +
            "65727333001053367881220235421809751254540594752243" +
            "52584907711670556013604839586446706324415722155397" +
            "53697817977846174064955149290862569321978468622482" +
            "83972241375657056057490261407972968652414535100474" +
            "82166370484403199890008895243450658541227588666881" +
            "16427171479924442928230863465674813919123162824586" +
            "17866458359124566529476545682848912883142607690042" +
            "24219022671055626321111109370544217506941658960408" +
            "07198403850962455444362981230987879927244284909188" +
            "84580156166097919133875499200524063689912560717606" +
            "05886116467109405077541002256983155200055935729725" +
            "71636269561882670428252483600823257530420752963450";
    public static void main(String[] args) {
        long start = System.currentTimeMillis();
        long result = solution(13);
        long end = System.currentTimeMillis();
        System.out.println("Result: " + result + " (done in " + (end - start) + "ms)");
    }

    private static long solution(int size) {
        long currentProduct = calculateProductAtIndex(0, size),
            currentGreatest = currentProduct;

        for (int i = 1; i < NUMBER.length() - size; i++) {
            currentProduct = calculateProductAtIndex(i, size);
            if (currentProduct > currentGreatest)
                currentGreatest = currentProduct;
        }
        return currentGreatest;
    }

    private static long calculateProductAtIndex(int startIndex, int size) {
        long currentProduct = 1;
        for (int i = startIndex; i < size + startIndex; i++) {
            int current = Integer.valueOf(NUMBER.substring(i, i+1));
            currentProduct *= current;
        }
        return currentProduct;
    }
}