Longest Common Substring

LCS.java

public class LCS {
 
    public static void main(String... args) throws Exception {
        System.out.println(lcs("Milexxs", "xxxxxxxM"));
    }

    public static String lcs(String a, String b) {
        if (null == a || null == b) return "";
        String longest = "";
        for (int i = 0; i < a.length(); ++i) {
            for (int j = 0; j < b.length(); ++j) {
                int k;
                for (k = 0; i + k < a.length() && j + k < b.length(); ++k) {
                    if (a.charAt(i+k) != b.charAt(j+k)) {
                        break;
                    }
                }
                if (k > longest.length()) {
                    longest = a.substring(i, i + k);
                }
            }
        }
        return max;
    }
}