java8 Stream接口简介

首先我们先来认识下一个的接口的意思，流是什么？

流是java API中的新的成员，它可以让你用声明式的方式处理集合，简单点说，可以看成遍历数据的一个高级点的迭代器，也可以看做一个工厂，数据处理的工厂，当然，流还天然的支持并行操作；也就不用去写复杂的多线程的代码，下面我先来看下stream的接口定义

public interface Stream<T> extends BaseStream<T, Stream<T>> {

	Stream<T> filter(Predicate<? super T> predicate);

	<R> Stream<R> map(Function<? super T, ? extends R> mapper);

	IntStream mapToInt(ToIntFunction<? super T> mapper);

	LongStream mapToLong(ToLongFunction<? super T> mapper);

	DoubleStream mapToDouble(ToDoubleFunction<? super T> mapper);

	<R> Stream<R> flatMap(Function<? super T, ? extends Stream<? extends R>> mapper);

	IntStream flatMapToInt(Function<? super T, ? extends IntStream> mapper);

	LongStream flatMapToLong(Function<? super T, ? extends LongStream> mapper);

	DoubleStream flatMapToDouble(Function<? super T, ? extends DoubleStream> mapper);

	Stream<T> distinct();

	Stream<T> sorted();

	Stream<T> sorted(Comparator<? super T> comparator);

	Stream<T> peek(Consumer<? super T> action);

	Stream<T> limit(long maxSize);

	Stream<T> skip(long n);

	void forEach(Consumer<? super T> action);

	void forEachOrdered(Consumer<? super T> action);

	Object[] toArray();

	<A> A[] toArray(IntFunction<A[]> generator);

	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);

	<R> R collect(Supplier<R> supplier, BiConsumer<R, ? super T> accumulator, BiConsumer<R, R> combiner);

	<R, A> R collect(Collector<? super T, A, R> collector);

	Optional<T> min(Comparator<? super T> comparator);

	Optional<T> max(Comparator<? super T> comparator);

	long count();

	boolean anyMatch(Predicate<? super T> predicate);

	boolean allMatch(Predicate<? super T> predicate);

	boolean noneMatch(Predicate<? super T> predicate);

	Optional<T> findFirst();

	Optional<T> findAny();

	public static <T> Builder<T> builder() {
		return new Streams.StreamBuilderImpl<>();
	}

	public static <T> Stream<T> empty() {
		return StreamSupport.stream(Spliterators.<T> emptySpliterator(), false);
	}

	public static <T> Stream<T> of(T t) {
		return StreamSupport.stream(new Streams.StreamBuilderImpl<>(t), false);
	}

	@SafeVarargs
	@SuppressWarnings("varargs") // Creating a stream from an array is safe
	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);
	}

	public static <T> Stream<T> concat(Stream<? extends T> a, Stream<? extends T> b) {
		Objects.requireNonNull(a);
		Objects.requireNonNull(b);

		@SuppressWarnings("unchecked")
		Spliterator<T> split = new Streams.ConcatSpliterator.OfRef<>((Spliterator<T>) a.spliterator(),
				(Spliterator<T>) b.spliterator());
		Stream<T> stream = StreamSupport.stream(split, a.isParallel() || b.isParallel());
		return stream.onClose(Streams.composedClose(a, b));
	}

	public interface Builder<T> extends Consumer<T> {
		@Override
		void accept(T t);

		default Builder<T> add(T t) {
			accept(t);
			return this;
		}

		Stream<T> build();

	}
}

通过接口定义，可以看到，抽象方法，有30多个，里面还有一些其他的接口；后续，我会慢慢给大家介绍，每个抽象方法的作用，以及用法

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