@NonNull static String createUniqueFilename(String prefix){
  String randomId=Long.toString(System.currentTimeMillis());
  return String.format(Locale.US,FILE_NAME_TEMPLATE,prefix,randomId);
}

@ NonNull static String createUniqueFilename ( String prefix ) { String randomId = Long . toString ( System . currentTimeMillis ( ) ) ; return String . format ( Locale . US , FILE_NAME_TEMPLATE , prefix , randomId ) ; }
create a unique file name starting with the prefix .
