public static String getExtension(String filename) {final int idx = filename.indexOf('.');if (idx == -1) {return null;} else {return filename.substring(idx + 1, filename.length());}}
public static string GetExtension(string filename){int idx = filename.IndexOf('.');if (idx == -1){return null;}else{return filename.Substring(idx + 1, filename.Length - (idx + 1));}}