code: public void start() {
  		synchronized (this.monitor) {
  			saveInitialSnapshots();
  			if (this.watchThread == null) {
  				Map<File, FolderSnapshot> localFolders = new HashMap<>();
  				localFolders.putAll(this.folders);
  				this.watchThread = new Thread(new Watcher(this.remainingScans,
  						new ArrayList<>(this.listeners), this.triggerFilter,
  						this.pollInterval, this.quietPeriod, localFolders));
  				this.watchThread.setName("File Watcher");
  				this.watchThread.setDaemon(this.daemon);
  				this.watchThread.start();
  			}
  		}
  	}
docs: Start monitoring the source folder for changes.