Package com.google.common.collect

Class Streams

  • @GwtCompatible
public final class Streams
extends Object
    Static utility methods related to Stream instances.
    Since:
    33.4.0 (but since 21.0 in the JRE flavor)

    • Method Detail

      • stream

        public static <T extends @Nullable Object> Stream<T> stream​(Iterator<T> iterator)
        Returns a sequential Stream of the remaining contents of iterator. Do not use iterator directly after passing it to this method.

      • stream

        public static <T> Stream<T> stream​(Optional<T> optional)
        If a value is present in optional, returns a stream containing only that element, otherwise returns an empty stream.

      • stream

        @Beta
@InlineMe(replacement="optional.stream()")
public static <T> Stream<T> stream​(Optional<T> optional)
        If a value is present in optional, returns a stream containing only that element, otherwise returns an empty stream.

        Java 9 users: use optional.stream() instead.

      • stream

        @Beta
@InlineMe(replacement="optional.stream()")
public static IntStream stream​(OptionalInt optional)
        If a value is present in optional, returns a stream containing only that element, otherwise returns an empty stream.

        Java 9 users: use optional.stream() instead.

      • stream

        @Beta
@InlineMe(replacement="optional.stream()")
public static LongStream stream​(OptionalLong optional)
        If a value is present in optional, returns a stream containing only that element, otherwise returns an empty stream.

        Java 9 users: use optional.stream() instead.

      • concat

        public static IntStream concat​(IntStream... streams)
        Returns an IntStream containing the elements of the first stream, followed by the elements of the second stream, and so on.

        This is equivalent to Stream.of(streams).flatMapToInt(stream -> stream), but the returned stream may perform better.

        See Also:
        IntStream.concat(IntStream, IntStream)

      • forEachPair

        @Beta
public static <A extends @Nullable Object,​B extends @Nullable Object> void forEachPair​(Stream<A> streamA,
                                                                                             Stream<B> streamB,
                                                                                             BiConsumer<? super A,​? super B> consumer)
        Invokes consumer once for each pair of corresponding elements in streamA and streamB. If one stream is longer than the other, the extra elements are silently ignored. Elements passed to the consumer are guaranteed to come from the same position in their respective source streams. For example: 
        
 Streams.forEachPair(
   Stream.of("foo1", "foo2", "foo3"),
   Stream.of("bar1", "bar2"),
   (arg1, arg2) -> System.out.println(arg1 + ":" + arg2)

        will print: 

        
 foo1:bar1
 foo2:bar2

        Warning: If either supplied stream is a parallel stream, the same correspondence between elements will be made, but the order in which those pairs of elements are passed to the consumer is not defined.

        Note that many usages of this method can be replaced with simpler calls to zip(java.util.stream.Stream<A>, java.util.stream.Stream<B>, java.util.function.BiFunction<? super A, ? super B, R>). This method behaves equivalently to zipping the stream elements into temporary pair objects and then using Stream.forEach(java.util.function.Consumer<? super T>) on that stream.

        Since:
        33.4.0 (but since 22.0 in the JRE flavor)

      • mapWithIndex

        public static <T extends @Nullable Object,​R extends @Nullable Object> Stream<R> mapWithIndex​(Stream<T> stream,
                                                                                                   Streams.FunctionWithIndex<? super T,​? extends R> function)
        Returns a stream consisting of the results of applying the given function to the elements of stream and their indices in the stream. For example, 
        
 mapWithIndex(
     Stream.of("a", "b", "c"),
     (e, index) -> index + ":" + e)

        would return Stream.of("0:a", "1:b", "2:c").

        The resulting stream is efficiently splittable if and only if stream was efficiently splittable and its underlying spliterator reported Spliterator.SUBSIZED. This is generally the case if the underlying stream comes from a data structure supporting efficient indexed random access, typically an array or list.

        The order of the resulting stream is defined if and only if the order of the original stream was defined.

      • mapWithIndex

        public static <R extends @Nullable Object> Stream<R> mapWithIndex​(IntStream stream,
                                                                  Streams.IntFunctionWithIndex<R> function)
        Returns a stream consisting of the results of applying the given function to the elements of stream and their indexes in the stream. For example, 
        
 mapWithIndex(
     IntStream.of(10, 11, 12),
     (e, index) -> index + ":" + e)

        ...would return Stream.of("0:10", "1:11", "2:12").

        The resulting stream is efficiently splittable if and only if stream was efficiently splittable and its underlying spliterator reported Spliterator.SUBSIZED. This is generally the case if the underlying stream comes from a data structure supporting efficient indexed random access, typically an array or list.

        The order of the resulting stream is defined if and only if the order of the original stream was defined.

      • mapWithIndex

        public static <R extends @Nullable Object> Stream<R> mapWithIndex​(LongStream stream,
                                                                  Streams.LongFunctionWithIndex<R> function)
        Returns a stream consisting of the results of applying the given function to the elements of stream and their indexes in the stream. For example, 
        
 mapWithIndex(
     LongStream.of(10, 11, 12),
     (e, index) -> index + ":" + e)

        ...would return Stream.of("0:10", "1:11", "2:12").

        The resulting stream is efficiently splittable if and only if stream was efficiently splittable and its underlying spliterator reported Spliterator.SUBSIZED. This is generally the case if the underlying stream comes from a data structure supporting efficient indexed random access, typically an array or list.

        The order of the resulting stream is defined if and only if the order of the original stream was defined.

      • mapWithIndex

        public static <R extends @Nullable Object> Stream<R> mapWithIndex​(DoubleStream stream,
                                                                  Streams.DoubleFunctionWithIndex<R> function)
        Returns a stream consisting of the results of applying the given function to the elements of stream and their indexes in the stream. For example, 
        
 mapWithIndex(
     DoubleStream.of(0.0, 1.0, 2.0)
     (e, index) -> index + ":" + e)

        ...would return Stream.of("0:0.0", "1:1.0", "2:2.0").

        The resulting stream is efficiently splittable if and only if stream was efficiently splittable and its underlying spliterator reported Spliterator.SUBSIZED. This is generally the case if the underlying stream comes from a data structure supporting efficient indexed random access, typically an array or list.

        The order of the resulting stream is defined if and only if the order of the original stream was defined.

      • findLast

        public static <T> Optional<T> findLast​(Stream<T> stream)
        Returns the last element of the specified stream, or Optional.empty() if the stream is empty.

        Equivalent to stream.reduce((a, b) -> b), but may perform significantly better. This method's runtime will be between O(log n) and O(n), performing better on efficiently splittable streams.

        If the stream has nondeterministic order, this has equivalent semantics to Stream.findAny() (which you might as well use).

        Throws:
        NullPointerException - if the last element of the stream is null
        See Also:
        Stream.findFirst()