public static String getFileExtension(String _fileName) {
        if (_fileName == null) {
            return null;
        }
        int lastDot = _fileName.lastIndexOf('.');
        if (lastDot == -1) {
            return "";
        }
        return _fileName.substring(lastDot + 1);
    }
public static String getFileExtension ( String _fileName ) { if ( _fileName == null ) { return null ; } int lastDot = _fileName . lastIndexOf ( '.' ) ; if ( lastDot == - 1 ) { return "" ; } return _fileName . substring ( lastDot + 1 ) ; }
Extracts the file extension (part behind last dot of a filename).
Only returns the extension, without the leading dot.

@param _fileName filename
@return extension, empty string if not dot was found in filename or null if given String was null