上期咱們分析了Java8中的引用,本期咱們將分析Java8中的另外一個重要的新特性:流Stream。 本文
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轉載自併發編程網java
在Java8源代碼中,是這麼定義Stream的:編程
A sequence of elements supporting sequential and parallel aggregate operations.微信
簡單翻譯就是流是支持順序和並行的匯聚操做的一組元素。併發
從這個定義上來講,Stream
能夠說是一個高級版本的Iterator
,Iterator只能一個一個遍歷元素從而對元素進行操做,可是Stream能夠執行很是複雜的查找、過濾和映射數據等操做,而且中間操做能夠一直迭代。app
Collections是存儲元素,Stream是計算。ide
Stream能夠理解爲一個管道(Pipeline
),數據從管道的一邊進入,通過中間各類處理,而後從管道的另外一邊出來新的數據。函數
幾個注意點:性能
default Stream<E> stream() {
return StreamSupport.stream(spliterator(), false);
}
default Stream<E> parallelStream() {
return StreamSupport.stream(spliterator(), true);
}
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public static <T> Stream<T> stream(T[] array) {
return stream(array, 0, array.length);
}
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public static<T> Stream<T> of(T t) {
return StreamSupport.stream(new Streams.StreamBuilderImpl<>(t), false);
}
public static<T> Stream<T> of(T... values) {
return Arrays.stream(values);
}
public static<T> Stream<T> iterate(final T seed, final UnaryOperator<T> f) {
Objects.requireNonNull(f);
final Iterator<T> iterator = new Iterator<T>() {
@SuppressWarnings("unchecked")
T t = (T) Streams.NONE;
@Override
public boolean hasNext() {
return true;
}
@Override
public T next() {
return t = (t == Streams.NONE) ? seed : f.apply(t);
}
};
return StreamSupport.stream(Spliterators.spliteratorUnknownSize(
iterator,
Spliterator.ORDERED | Spliterator.IMMUTABLE), false);
}
public static<T> Stream<T> generate(Supplier<T> s) {
Objects.requireNonNull(s);
return StreamSupport.stream(
new StreamSpliterators.InfiniteSupplyingSpliterator.OfRef<>(Long.MAX_VALUE, s), false);
}
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Stream<T> filter(Predicate<? super T> predicate);
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Stream<T> distinct();
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Stream<T> limit(long maxSize);
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Stream<T> skip(long n);
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是否是有點相似SQL語句呢?測試
<R> Stream<R> map(Function<? super T, ? extends R> mapper);
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mapToIntui
mapToLong
mapToDouble
flatMap
<R> Stream<R> flatMap(Function<? super T, ? extends Stream<? extends R>> mapper);
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Stream<T> sorted();
Stream<T> sorted(Comparator<? super T> comparator);
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Stream<T> peek(Consumer<? super T> action);
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boolean allMatch(Predicate<? super T> predicate);
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boolean anyMatch(Predicate<? super T> predicate);
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boolean noneMatch(Predicate<? super T> predicate);
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Optional<T> findFirst();
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Optional<T> findAny();
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long count();
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Optional<T> max(Comparator<? super T> comparator);
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Optional<T> min(Comparator<? super T> comparator);
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void forEach(Consumer<? super T> action);
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T reduce(T identity, BinaryOperator<T> accumulator);
Optional<T> reduce(BinaryOperator<T> accumulator);
<U> U reduce(U identity, BiFunction<U, ? super T, U> accumulator, BinaryOperator<U> combiner);
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<R, A> R collect(Collector<? super T, A, R> collector);
<R> R collect(Supplier<R> supplier, BiConsumer<R, ? super T> accumulator, BiConsumer<R, R> combiner);
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List<T> toList() Set<T> toSet() Collection<T> toCollection Long counting Integer summingInt Double averagingInt IntSummaryStatistics summarizingInt String joining Optional<T> maxBy Optional<T> minBy ... 複製代碼
Stream是否是很方便呢? 下期咱們將測試下Stream中串行流與並行流的性能