java8-Stream

匿名内部类和lambda表达式

        new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println(Thread.currentThread().getName());
            }
        });

        new Thread(() -> {
            System.out.println(Thread.currentThread().getName());
        }).start();

函数式接口

@FunctionalInterface

只允许有一个抽象方法，例如Runable和Callable接口。

@FunctionalInterface
public interface Runnable {

    public abstract void run();
}

@FunctionalInterface
public interface Callable<V> {
  
    V call() throws Exception;
}

继承关系如图所示

public interface AutoCloseable {

    void close() throws Exception;
}

public interface BaseStream<T, S extends BaseStream<T, S>>
        extends AutoCloseable {
         
    Iterator<T> iterator();
  
    Spliterator<T> spliterator();
      
    boolean isParallel();
  
    S sequential();
    
    S parallel();
    
    S unordered();
  
    S onClose(Runnable closeHandler);
   
    @Override
    void close();
}

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> 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();

    }
}

Stream接口中有内部接口Builder，其继承关系如图所示

注解FunctionalInterface，作用用于标识函数式接口

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface FunctionalInterface {}

Consumer接口是一个函数式接口，

@FunctionalInterface
public interface Consumer<T> {

    void accept(T t);
       
    default Consumer<T> andThen(Consumer<? super T> after) {
        Objects.requireNonNull(after);
        return (T t) -> { accept(t); after.accept(t); };
    }
}

Builder接口

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();

    }

Predicate接口