@Override protected String extractKey(final String name){
  final String key=unescape(name.substring(0,name.length() - 4));
  return key.equals("\0") ? null : key;
}

@ Override protected String extractKey ( final String name ) { final String key = unescape ( name . substring ( 0 , name . length ( ) - 4 ) ) ; return key . equals ( "\0" ) ? null : key ; }
given a filename , the unescape method returns the key which originated it .
