code: void rollOver() throws IOException {
  
  		// If compression is enabled we start a separated thread
  		if (getCompressBackups().equalsIgnoreCase("YES")
  				|| getCompressBackups().equalsIgnoreCase("TRUE")) {
  			File file = new File(fileName);
  			Thread fileCompressor = new Thread(new CompressFile(file));
  			fileCompressor.start();
  		}
  
  		/* Compute filename, but only if datePattern is specified */
  		if (datePattern == null) {
  			errorHandler.error("Missing DatePattern option in rollOver().");
  			return;
  		}
  
  		String datedFilename = baseFileName + sdf.format(now);
  		// It is too early to roll over because we are still within the
  		// bounds of the current interval. Rollover will occur once the
  		// next interval is reached.
  		if (scheduledFilename.equals(datedFilename)) {
  			return;
  		}
  
  		activateOptions();
  	}
docs: Rollover the current file to a new file.