我正在寻找一种简洁的方法来将 a 转换Iterator为 aStream或更具体地说是将迭代器“查看”为流。
Iterator
Stream
出于性能原因,我想避免在新列表中复制迭代器:
Iterator<String> sourceIterator = Arrays.asList("A", "B", "C").iterator(); Collection<String> copyList = new ArrayList<String>(); sourceIterator.forEachRemaining(copyList::add); Stream<String> targetStream = copyList.stream();
根据评论中的一些建议,我也尝试使用Stream.generate:
Stream.generate
public static void main(String[] args) throws Exception { Iterator<String> sourceIterator = Arrays.asList("A", "B", "C").iterator(); Stream<String> targetStream = Stream.generate(sourceIterator::next); targetStream.forEach(System.out::println); }
但是,我得到一个NoSuchElementException(因为没有调用hasNext)
NoSuchElementException
hasNext
Exception in thread "main" java.util.NoSuchElementException at java.util.AbstractList$Itr.next(AbstractList.java:364) at Main$$Lambda$1/1175962212.get(Unknown Source) at java.util.stream.StreamSpliterators$InfiniteSupplyingSpliterator$OfRef.tryAdvance(StreamSpliterators.java:1351) at java.util.Spliterator.forEachRemaining(Spliterator.java:326) at java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:580) at Main.main(Main.java:20)
我看过,StreamSupport但Collections我没有找到任何东西。
StreamSupport
Collections
一种方法是从中创建一个Spliterator并将Iterator其用作流的基础:
Spliterator
Iterator<String> sourceIterator = Arrays.asList("A", "B", "C").iterator(); Stream<String> targetStream = StreamSupport.stream( Spliterators.spliteratorUnknownSize(sourceIterator, Spliterator.ORDERED), false);
另一种可能更具可读性的替代方法是使用- 并且使用 lambdas从 anIterable创建一个非常容易,因为它是一个函数式接口:Iterable``Iterator``Iterable
Iterable
Iterable``Iterator``Iterable
Iterator<String> sourceIterator = Arrays.asList("A", "B", "C").iterator(); Iterable<String> iterable = () -> sourceIterator; Stream<String> targetStream = StreamSupport.stream(iterable.spliterator(), false);