code: private boolean relevant(File currentLogFile, GregorianCalendar lastRelevantDate) {
  		String fileName=currentLogFile.getName();
  		Pattern p = Pattern.compile(APPENER_DATE_DEFAULT_PATTERN);
  		Matcher m = p.matcher(fileName);
  		if(m.find()){
  			int year=Integer.parseInt(m.group(1));
  			int month=Integer.parseInt(m.group(2));
  			int dayOfMonth=Integer.parseInt(m.group(3));
  			GregorianCalendar fileDate=new GregorianCalendar(year, month, dayOfMonth);
  			fileDate.add(Calendar.MONTH,-1); //Because of Calendar save the month such that January is 0
  			return fileDate.compareTo(lastRelevantDate)>0;
  		}
  		else{
  			return false;
  		}
  	}
docs: Get a log file and last relevant date, and check if the log file is relevant
  @param currentLogFile The log file
  @param lastRelevantDate The last date which files should be keeping since
  @return false if the file should be deleted, true if it does not.