Longest Contiguous Subarray

int[] longest(int[] a) {
    if (a == null) return null;
    int longestIndex = -1, longestLength = 0;
    for (int i = 0; i < a.length; ++i) {
        int sum = 0;
        int length = 0;
        for (int j = i; j < a.length; ++j) {
            sum += a[j];
            ++length;
            if (sum >= 0 && length > longestLength) {
                longestIndex = i;
                longestLength = length;
            }
        }
    }
    if (longestIndex == -1) return null;
    int[] b = new int[longestLength];
    for (int i = 0; i < longestLength; ++i) b[i] = a[i + longestIndex];
    return b;
}