Package com.google.common.collect

Class Streams

com.google.common.collect.Streams

@GwtCompatible
public final class Streams
extends 

Static utility methods related to Stream instances.

Since:

21.0

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static interface	Streams.DoubleFunctionWithIndex<R>	An analogue of also accepting an index.
static interface	Streams.FunctionWithIndex<T,R>	An analogue of also accepting an index.
static interface	Streams.IntFunctionWithIndex<R>	An analogue of also accepting an index.
static interface	Streams.LongFunctionWithIndex<R>	An analogue of also accepting an index.

Method Summary

Modifier and Type	Method	Description
static	... streams)	Returns a containing the elements of the first stream, followed by the elements of the second stream, and so on.
static	... streams)	Returns an containing the elements of the first stream, followed by the elements of the second stream, and so on.
static	... streams)	Returns a containing the elements of the first stream, followed by the elements of the second stream, and so on.
static <T> <T>	<? extends T>... streams)	Returns a containing the elements of the first stream, followed by the elements of the second stream, and so on.
static	stream)	Returns the last element of the specified stream, or if the stream is empty.
static	stream)	Returns the last element of the specified stream, or if the stream is empty.
static	stream)	Returns the last element of the specified stream, or if the stream is empty.
static <T> <T>	<T> stream)	Returns the last element of the specified stream, or if the stream is empty.
static <A,B> void	<A> streamA, <B> streamB, <? super A,? super B> consumer)	Invokes consumer once for each pair of corresponding elements in streamA and streamB.
static <R> <R>	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.
static <R> <R>	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.
static <R> <R>	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.
static <T,R> <R>	<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.
static <T> <T>	stream(Optional<T> optional)	If a value is present in optional, returns a stream containing only that element, otherwise returns an empty stream.
static <T> <T>	<T> iterable)	Returns a sequential of the contents of iterable, delegating to if possible.
static <T> <T>	<T> collection)	Deprecated. There is no reason to use this; just invoke collection.stream() directly.
static <T> <T>	<T> iterator)	Returns a sequential of the remaining contents of iterator.
static <T> <T>	<T> optional)	If a value is present in optional, returns a stream containing only that element, otherwise returns an empty stream.
static	optional)	If a value is present in optional, returns a stream containing only that element, otherwise returns an empty stream.
static	optional)	If a value is present in optional, returns a stream containing only that element, otherwise returns an empty stream.
static	optional)	If a value is present in optional, returns a stream containing only that element, otherwise returns an empty stream.
static <A,B,R> <R>	<A> streamA, <B> streamB, <? super A,? super B,R> function)	Returns a stream in which each element is the result of passing the corresponding element of each of streamA and streamB to function.

Methods inherited from class java.lang.

, , , , , , , , , ,

Method Detail

stream

public static <T> <T> <T> iterable)

Returns a sequential of the contents of iterable, delegating to if possible.

stream

@Beta

public static <T> <T> <T> collection)

Deprecated.

There is no reason to use this; just invoke collection.stream() directly.

Returns .

stream

@Beta
public static <T> <T> <T> iterator)

Returns a sequential of the remaining contents of iterator. Do not use iterator directly after passing it to this method.

stream

@Beta
public static <T> <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
public static <T> <T> <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
public static   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
public static   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
public static   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 <T> <T> <? extends T>... streams)

Returns a 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).flatMap(stream -> stream), but the returned stream may perform better.

See Also:

concat

public static  ... streams)

Returns an 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:

concat

public static  ... streams)

Returns a 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).flatMapToLong(stream -> stream), but the returned stream may perform better.

See Also:

concat

public static  ... streams)

Returns a 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).flatMapToDouble(stream -> stream), but the returned stream may perform better.

See Also:

zip

@Beta
public static <A,B,R> <R> <A> streamA,
                                                <B> streamB,
                                                <? super A,? super B,R> function)

Returns a stream in which each element is the result of passing the corresponding element of each of streamA and streamB to function.

For example:

 Streams.zip(
   Stream.of("foo1", "foo2", "foo3"),
   Stream.of("bar1", "bar2"),
   (arg1, arg2) -> arg1 + ":" + arg2)
 

will return Stream.of("foo1:bar1", "foo2:bar2").

The resulting stream will only be as long as the shorter of the two input streams; if one stream is longer, its extra elements will be ignored.

Note that if you are calling on the resulting stream, you might want to consider using forEachPair(java.util.stream.Stream<A>, java.util.stream.Stream<B>, java.util.function.BiConsumer<? super A, ? super B>) instead of this method.

Performance note: The resulting stream is not . This may harm parallel performance.

forEachPair

@Beta
public static <A,B> void <A> streamA,
                                           <B> streamB,
                                           <? 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 on that stream.

Since:

22.0

mapWithIndex

@Beta
public static <T,R> <R> <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"),
     (str, index) -> str + ":" + index)
 

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

The resulting stream is if and only if stream was efficiently splittable and its underlying spliterator reported . 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

@Beta
public static <R> <R>  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(0, 1, 2),
     (i, index) -> i + ":" + index)
 

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

The resulting stream is if and only if stream was efficiently splittable and its underlying spliterator reported . 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

@Beta
public static <R> <R>  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(0, 1, 2),
     (i, index) -> i + ":" + index)
 

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

The resulting stream is if and only if stream was efficiently splittable and its underlying spliterator reported . 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

@Beta
public static <R> <R>  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, 1, 2),
     (x, index) -> x + ":" + index)
 

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

The resulting stream is if and only if stream was efficiently splittable and its underlying spliterator reported . 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

@Beta
public static <T> <T> <T> stream)

Returns the last element of the specified stream, or 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 streams.

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

Throws:

- if the last element of the stream is null

See Also:

findLast

@Beta
public static   stream)

Returns the last element of the specified stream, or 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 streams.

Throws:

- if the last element of the stream is null

See Also:

findLast

@Beta
public static   stream)

Returns the last element of the specified stream, or 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 streams.

Throws:

- if the last element of the stream is null

See Also:

findLast

@Beta
public static   stream)

Returns the last element of the specified stream, or 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 streams.

Throws:

- if the last element of the stream is null

See Also: