public boolean isEmpty(){
  if (lastBatch != null) {
    if (!lastBatch.isEmpty()) {
      return false;
    }
  }
  return currentBatch.isEmpty();
}

public boolean isEmpty ( ) { if ( lastBatch != null ) { if ( ! lastBatch . isEmpty ( ) ) { return false ; } } return currentBatch . isEmpty ( ) ; }
returns true if the window is empty , or false if not empty .
