code: private synchronized boolean poll(long currentTimeMillis) {
  		long timeDiffMillis = currentTimeMillis - _lastPolled;
  		if (timeDiffMillis > POLL_THRESHOLD_MILLIS) {
  			final long lastModifiedBefore = _lastModified;
  			_lastModified = _file.lastModified();
  			_lastPolled = System.currentTimeMillis();
  
  			return _lastModified != lastModifiedBefore;
  		}
  		return false;
  	}
docs: Polls the file system for a file change (synchronized)
  
  @param currentTimeMillis
  
  @return true if the file has changed