question: public void checkAndNotify ( ) { for ( FileAlterationListener listener : listeners ) { listener . onStart ( this ) ; } File rootFile = rootEntry . getFile ( ) ; if ( rootFile . exists ( ) ) { checkAndNotify ( rootEntry , rootEntry . getChildren ( ) , listFiles ( rootFile ) ) ; } else if ( rootEntry . isExists ( ) ) { checkAndNotify ( rootEntry , rootEntry . getChildren ( ) , FileUtils . EMPTY_FILE_ARRAY ) ; } else { } for ( FileAlterationListener listener : listeners ) { listener . onStop ( this ) ; } }
target:  Check whether the file and its chlidren have been created, modified or deleted.