我正在嘗試了解 SplitIterator 的功能并遇到以下情況：public static void main(String[] args) {    Set<Integer> l = new HashSet();    l.add(1);    l.add(2);    l.add(3);    Spliterator<Integer> s= (Spliterator<Integer>) l.spliterator();Spliterator<Integer> s1=s.trySplit();while(s1.tryAdvance(n -> {System.out.print(n+" ");System.out.println("estimateSize "+s.estimateSize()+" getexactsizeifknown "+s.getExactSizeIfKnown());})); 為什么該方法getexactsizeifknown返回-1for HashSet？對于其他集合，它返回與estimateSIze()