code: public void addSourceFolders(Iterable<File> folders) {
  		Assert.notNull(folders, "Folders must not be null");
  		synchronized (this.monitor) {
  			for (File folder : folders) {
  				addSourceFolder(folder);
  			}
  		}
  	}
docs: Add source folders to monitor. Cannot be called after the watcher has been
  {@link #start() started}.
  @param folders the folders to monitor