code: private void addBackup() {
          // move the current log file to the newly formatted backup name
          String newname = this.fileinfo + this.myFormat.format(new Date(HttpDispatcher.getApproxTime())) + this.extensioninfo;
          File newFile = new File(newname);
          renameFile(this.myFile, newFile);
          // now see if we need to delete an existing backup to make room
          if (this.backups.size() == getMaximumBackupFiles()) {
              File oldest = this.backups.removeLast();
              if (null != oldest && oldest.exists()) {
                  if (TraceComponent.isAnyTracingEnabled() && tc.isDebugEnabled()) {
                      Tr.debug(tc, getFileName() + ": Purging oldest backup-> " + oldest.getName());
                  }
                  oldest.delete();
              }
          }
          this.backups.addFirst(newFile);
          if (TraceComponent.isAnyTracingEnabled() && tc.isDebugEnabled()) {
              Tr.debug(tc, getFileName() + ": number of backup files-> " + this.backups.size());
          }
      }
docs: Move the current logfile to a backup name, taking care of any existing
  backup files according to the configured limit.