Spec-Zone .ru
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|
public interface DoubleStream
filter
and map
, and terminal
operations (consuming the contents of a stream to produce a result or
side-effect), such as forEach
, findFirst
, and iterator
. Once an operation has been performed on a stream, it
is considered consumed and no longer usable for other operations.
For sequential stream pipelines, all operations are performed in the encounter order of the pipeline source, if the pipeline source has a defined encounter order.
For parallel stream pipelines, unless otherwise specified, intermediate
stream operations preserve the
encounter order of their source, and terminal operations
respect the encounter order of their source, if the source
has an encounter order. Provided that and parameters to stream operations
satisfy the non-interference
requirements, and excepting differences arising from the absence of
a defined encounter order, the result of a stream pipeline should be the
stable across multiple executions of the same operations on the same source.
However, the timing and thread in which side-effects occur (for those
operations which are allowed to produce side-effects, such as
forEach(DoubleConsumer)
), are explicitly nondeterministic for parallel
execution of stream pipelines.
Unless otherwise noted, passing a null
argument to any stream
method may result in a NullPointerException
.
iterator()
or spliterator()
operations to
perform a controlled traversal.Modifier and Type | Method and Description |
---|---|
boolean |
allMatch(DoublePredicate predicate)
Returns whether all elements of this stream match the provided predicate.
|
boolean |
anyMatch(DoublePredicate predicate)
Returns whether any elements of this stream match the provided
predicate.
|
OptionalDouble |
average()
Returns an
OptionalDouble describing the average of elements of
this stream, or an empty optional if this stream is empty. |
Stream<Double> |
boxed()
Returns a
Stream consisting of the elements of this stream,
boxed to Double . |
static StreamBuilder.OfDouble |
builder()
Returns a builder for a
DoubleStream . |
<R> R |
collect(Supplier<R> resultFactory,
ObjDoubleConsumer<R> accumulator,
BiConsumer<R,R> combiner)
Performs a mutable
reduction operation on the elements of this stream.
|
long |
count()
Returns the count of elements in this stream.
|
DoubleStream |
distinct()
Returns a stream consisting of the distinct elements of this stream.
|
static DoubleStream |
empty()
Returns an empty sequential
DoubleStream . |
DoubleStream |
filter(DoublePredicate predicate)
Returns a stream consisting of the elements of this stream that match
the given predicate.
|
OptionalDouble |
findAny()
Returns an
OptionalDouble describing some element of the stream,
or an empty OptionalDouble if the stream is empty. |
OptionalDouble |
findFirst()
Returns an
OptionalDouble describing the first element of this
stream (in the encounter order), or an empty OptionalDouble if
the stream is empty. |
DoubleStream |
flatMap(DoubleFunction<? extends DoubleStream> mapper)
Returns a stream consisting of the results of replacing each element of
this stream with the contents of the stream produced by applying the
provided mapping function to each element.
|
void |
forEach(DoubleConsumer action)
Performs an action for each element of this stream.
|
void |
forEachOrdered(DoubleConsumer action)
Performs an action for each element of this stream, guaranteeing that
each element is processed in encounter order for streams that have a
defined encounter order.
|
static DoubleStream |
generate(DoubleSupplier s)
Returns a sequential
DoubleStream where each element is
generated by an DoubleSupplier . |
boolean |
isParallel()
Returns whether this stream, when executed, would execute in parallel
(assuming no further modification of the stream, such as appending
further intermediate operations or changing its parallelism).
|
static DoubleStream |
iterate(double seed,
DoubleUnaryOperator f)
Returns an infinite sequential
DoubleStream produced by iterative
application of a function f to an initial element seed ,
producing a Stream consisting of seed , f(seed) ,
f(f(seed)) , etc. |
PrimitiveIterator.OfDouble |
iterator()
Returns an iterator for the elements of this stream.
|
DoubleStream |
limit(long maxSize)
Returns a stream consisting of the elements of this stream, truncated
to be no longer than
maxSize in length. |
DoubleStream |
map(DoubleUnaryOperator mapper)
Returns a stream consisting of the results of applying the given
function to the elements of this stream.
|
IntStream |
mapToInt(DoubleToIntFunction mapper)
Returns an
IntStream consisting of the results of applying the
given function to the elements of this stream. |
LongStream |
mapToLong(DoubleToLongFunction mapper)
Returns a
LongStream consisting of the results of applying the
given function to the elements of this stream. |
<U> Stream<U> |
mapToObj(DoubleFunction<? extends U> mapper)
Returns an object-valued
Stream consisting of the results of
applying the given function to the elements of this stream. |
OptionalDouble |
max()
Returns an
OptionalDouble describing the maximum element of this
stream, or an empty OptionalDouble if this stream is empty. |
OptionalDouble |
min()
Returns an
OptionalDouble describing the minimum element of this
stream, or an empty OptionalDouble if this stream is empty. |
boolean |
noneMatch(DoublePredicate predicate)
Returns whether no elements of this stream match the provided predicate.
|
static DoubleStream |
of(double... values)
Returns a sequential stream whose elements are the specified values.
|
static DoubleStream |
of(double t)
Returns a sequential
DoubleStream containing a single element. |
DoubleStream |
parallel()
Returns an equivalent stream that is parallel.
|
DoubleStream |
peek(DoubleConsumer consumer)
Returns a stream consisting of the elements of this stream, additionally
performing the provided action on each element as elements are consumed
from the resulting stream.
|
static DoubleStream |
range(double startInclusive,
double endExclusive)
Returns a sequential
DoubleStream from startInclusive (inclusive)
to endExclusive (exclusive) by an incremental step of 1.0. |
static DoubleStream |
range(double startInclusive,
double endExclusive,
double step)
Returns a sequential
DoubleStream from startInclusive
(inclusive) to endExclusive (exclusive) by step . |
OptionalDouble |
reduce(DoubleBinaryOperator op)
Performs a reduction on the
elements of this stream, using an
associative accumulation
function, and returns an
OptionalDouble describing the reduced
value, if any. |
double |
reduce(double identity,
DoubleBinaryOperator op)
Performs a reduction on the
elements of this stream, using the provided identity value and an
associative
accumulation function, and returns the reduced value.
|
DoubleStream |
sequential()
Returns an equivalent stream that is sequential.
|
DoubleStream |
sorted()
Returns a stream consisting of the elements of this stream in sorted
order.
|
Spliterator.OfDouble |
spliterator()
Returns a spliterator for the elements of this stream.
|
DoubleStream |
substream(long startInclusive)
Returns a stream consisting of the remaining elements of this stream
after indexing
startInclusive elements into the stream. |
DoubleStream |
substream(long startInclusive,
long endExclusive)
Returns a stream consisting of the remaining elements of this stream
after indexing
startInclusive elements into the stream and
truncated to contain no more than endExclusive - startInclusive
elements. |
double |
sum()
Returns the sum of elements in this stream.
|
DoubleSummaryStatistics |
summaryStatistics()
Returns a
DoubleSummaryStatistics describing various summary data
about the elements of this stream. |
double[] |
toArray()
Returns an array containing the elements of this stream.
|
S |
unordered()
Returns an equivalent stream that is
unordered.
|
DoubleStream filter(DoublePredicate predicate)
This is an intermediate operation.
predicate
- a
non-interfering, stateless predicate to apply to
each element to determine if it should be includedDoubleStream map(DoubleUnaryOperator mapper)
This is an intermediate operation.
mapper
- a
non-interfering, stateless function to apply to
each element<U> Stream<U> mapToObj(DoubleFunction<? extends U> mapper)
Stream
consisting of the results of
applying the given function to the elements of this stream.
This is an intermediate operation.
U
- the element type of the new streammapper
- a
non-interfering, stateless function to apply to each
elementIntStream mapToInt(DoubleToIntFunction mapper)
IntStream
consisting of the results of applying the
given function to the elements of this stream.
This is an intermediate operation.
mapper
- a
non-interfering, stateless function to apply to each
elementLongStream mapToLong(DoubleToLongFunction mapper)
LongStream
consisting of the results of applying the
given function to the elements of this stream.
This is an intermediate operation.
mapper
- a
non-interfering, stateless function to apply to each
elementDoubleStream flatMap(DoubleFunction<? extends DoubleStream> mapper)
This is an intermediate operation.
flatMap()
operation has the effect of applying a one-to-many
tranformation to the elements of the stream, and then flattening the
resulting elements into a new stream. For example, if orders
is a stream of purchase orders, and each purchase order contains a
collection of line items, then the following produces a stream of line
items:
orderStream.flatMap(order -> order.getLineItems().stream())...
mapper
- a
non-interfering, stateless function to apply to
each element which produces an DoubleStream
of new
valuesStream.flatMap(Function)
DoubleStream distinct()
Double.compare(double, double)
.
This is a stateful intermediate operation.
DoubleStream sorted()
Double.compare(double, double)
.
This is a stateful intermediate operation.
DoubleStream peek(DoubleConsumer consumer)
This is an intermediate operation.
For parallel stream pipelines, the action may be called at whatever time and in whatever thread the element is made available by the upstream operation. If the action modifies shared state, it is responsible for providing the required synchronization.
list.stream()
.filter(filteringFunction)
.peek(e -> {System.out.println("Filtered value: " + e); });
.map(mappingFunction)
.peek(e -> {System.out.println("Mapped value: " + e); });
.collect(Collectors.toDoubleSummaryStastistics());
consumer
- a
non-interfering action to perform on the elements as
they are consumed from the streamDoubleStream limit(long maxSize)
maxSize
in length.
maxSize
- the number of elements the stream should be limited toIllegalArgumentException
- if maxSize
is negativeDoubleStream substream(long startInclusive)
startInclusive
elements into the stream. If the
startInclusive
index lies past the end of this stream then an
empty stream will be returned.
This is a stateful intermediate operation.
startInclusive
- the number of leading elements to skipIllegalArgumentException
- if startInclusive
is negativeDoubleStream substream(long startInclusive, long endExclusive)
startInclusive
elements into the stream and
truncated to contain no more than endExclusive - startInclusive
elements. If the startInclusive
index lies past the end
of this stream then an empty stream will be returned.
startInclusive
- the starting position of the substream, inclusiveendExclusive
- the ending position of the substream, exclusiveIllegalArgumentException
- if startInclusive
or
endExclusive
is negative or startInclusive
is greater
than endExclusive
void forEach(DoubleConsumer action)
This is a terminal operation.
For parallel stream pipelines, this operation does not guarantee to respect the encounter order of the stream, as doing so would sacrifice the benefit of parallelism. For any given element, the action may be performed at whatever time and in whatever thread the library chooses. If the action accesses shared state, it is responsible for providing the required synchronization.
action
- a
non-interfering action to perform on the elementsvoid forEachOrdered(DoubleConsumer action)
This is a terminal operation.
action
- a
non-interfering action to perform on the elementsforEach(DoubleConsumer)
double[] toArray()
This is a terminal operation.
double reduce(double identity, DoubleBinaryOperator op)
double result = identity;
for (double element : this stream)
result = accumulator.apply(result, element)
return result;
but is not constrained to execute sequentially.
The identity
value must be an identity for the accumulator
function. This means that for all x
,
accumulator.apply(identity, x)
is equal to x
.
The accumulator
function must be an
associative function.
This is a terminal operation.
double sum = numbers.reduce(0, (a, b) -> a+b);
or more compactly:
double sum = numbers.reduce(0, Double::sum);
While this may seem a more roundabout way to perform an aggregation compared to simply mutating a running total in a loop, reduction operations parallelize more gracefully, without needing additional synchronization and with greatly reduced risk of data races.
identity
- the identity value for the accumulating functionop
- an associative
non-interfering,
stateless function for combining two valuessum()
,
min()
,
max()
,
average()
OptionalDouble reduce(DoubleBinaryOperator op)
OptionalDouble
describing the reduced
value, if any. This is equivalent to:
boolean foundAny = false;
double result = null;
for (double element : this stream) {
if (!foundAny) {
foundAny = true;
result = element;
}
else
result = accumulator.apply(result, element);
}
return foundAny ? OptionalDouble.of(result) : OptionalDouble.empty();
but is not constrained to execute sequentially.
The accumulator
function must be an
associative function.
This is a terminal operation.
op
- an associative
non-interfering,
stateless function for combining two valuesreduce(double, DoubleBinaryOperator)
<R> R collect(Supplier<R> resultFactory, ObjDoubleConsumer<R> accumulator, BiConsumer<R,R> combiner)
ArrayList
, and elements are incorporated by updating
the state of the result, rather than by replacing the result. This
produces a result equivalent to:
R result = resultFactory.get();
for (double element : this stream)
accumulator.accept(result, element);
return result;
Like reduce(double, DoubleBinaryOperator)
, collect
operations can be parallelized without requiring additional
synchronization.
This is a terminal operation.
R
- type of the resultresultFactory
- a function that creates a new result container.
For a parallel execution, this function may be
called multiple times and must return a fresh value
each time.accumulator
- an associative
non-interfering,
stateless function for incorporating an additional
element into a resultcombiner
- an associative
non-interfering,
stateless function for combining two values, which
must be compatible with the accumulator functionStream.collect(Supplier, BiConsumer, BiConsumer)
double sum()
NaN
or
the sum is at any point a NaN
then the sum will be NaN
.
This is a special case of a
reduction and is
equivalent to:
return reduce(0, Double::sum);
OptionalDouble min()
OptionalDouble
describing the minimum element of this
stream, or an empty OptionalDouble if this stream is empty. The minimum
element will be Double.NaN
if any stream element was NaN. Unlike
the numerical comparison operators, this method considers negative zero
to be strictly smaller than positive zero. This is a special case of a
reduction and is
equivalent to:
return reduce(Double::min);
OptionalDouble
containing the minimum element of this
stream, or an empty optional if the stream is emptyOptionalDouble max()
OptionalDouble
describing the maximum element of this
stream, or an empty OptionalDouble if this stream is empty. The maximum
element will be Double.NaN
if any stream element was NaN. Unlike
the numerical comparison operators, this method considers negative zero
to be strictly smaller than positive zero. This is a
special case of a
reduction and is
equivalent to:
return reduce(Double::max);
OptionalDouble
containing the maximum element of this
stream, or an empty optional if the stream is emptylong count()
return mapToLong(e -> 1L).sum();
This is a terminal operation.
OptionalDouble average()
OptionalDouble
describing the average of elements of
this stream, or an empty optional if this stream is empty. The average
returned can vary depending upon the order in which elements are
encountered. This is due to accumulated rounding error in addition of
elements of differing magnitudes. Elements sorted by increasing absolute
magnitude tend to yield more accurate results. If any recorded value is
a NaN
or the sum is at any point a NaN
then the average
will be NaN
. This is a special case of a
reduction.OptionalDouble
containing the average element of this
stream, or an empty optional if the stream is emptyDoubleSummaryStatistics summaryStatistics()
DoubleSummaryStatistics
describing various summary data
about the elements of this stream. This is a special
case of a reduction.DoubleSummaryStatistics
describing various summary data
about the elements of this streamboolean anyMatch(DoublePredicate predicate)
This is a short-circuiting terminal operation.
predicate
- a non-interfering,
stateless predicate to apply to elements of this
streamtrue
if any elements of the stream match the provided
predicate otherwise false
boolean allMatch(DoublePredicate predicate)
This is a short-circuiting terminal operation.
predicate
- a non-interfering,
stateless predicate to apply to elements of this
streamtrue
if all elements of the stream match the provided
predicate otherwise false
boolean noneMatch(DoublePredicate predicate)
This is a short-circuiting terminal operation.
predicate
- a non-interfering,
stateless predicate to apply to elements of this
streamtrue
if no elements of the stream match the provided
predicate otherwise false
OptionalDouble findFirst()
OptionalDouble
describing the first element of this
stream (in the encounter order), or an empty OptionalDouble
if
the stream is empty. If the stream has no encounter order, than any
element may be returned.
This is a short-circuiting terminal operation.
OptionalDouble
describing the first element of this
stream, or an empty OptionalDouble
if the stream is emptyOptionalDouble findAny()
OptionalDouble
describing some element of the stream,
or an empty OptionalDouble
if the stream is empty.
This is a short-circuiting terminal operation.
The behavior of this operation is explicitly nondeterministic; it is
free to select any element in the stream. This is to allow for maximal
performance in parallel operations; the cost is that multiple invocations
on the same source may not return the same result. (If the first element
in the encounter order is desired, use findFirst()
instead.)
OptionalDouble
describing some element of this stream,
or an empty OptionalDouble
if the stream is emptyfindFirst()
Stream<Double> boxed()
Stream
consisting of the elements of this stream,
boxed to Double
.Stream
consistent of the elements of this stream,
each boxed to a Double
DoubleStream sequential()
This is an intermediate operation.
DoubleStream parallel()
This is an intermediate operation.
PrimitiveIterator.OfDouble iterator()
This is a terminal operation.
Spliterator.OfDouble spliterator()
This is a terminal operation.
static StreamBuilder.OfDouble builder()
DoubleStream
.static DoubleStream empty()
DoubleStream
.static DoubleStream of(double t)
DoubleStream
containing a single element.t
- the single elementstatic DoubleStream of(double... values)
values
- the elements of the new streamstatic DoubleStream iterate(double seed, DoubleUnaryOperator f)
DoubleStream
produced by iterative
application of a function f
to an initial element seed
,
producing a Stream
consisting of seed
, f(seed)
,
f(f(seed))
, etc.
The first element (position 0
) in the DoubleStream
will be the provided seed
. For n > 0
, the element at
position n
, will be the result of applying the function f
to the element at position n - 1
.
seed
- the initial elementf
- a function to be applied to to the previous element to produce
a new elementDoubleStream
static DoubleStream generate(DoubleSupplier s)
DoubleStream
where each element is
generated by an DoubleSupplier
. This is suitable for generating
constant streams, streams of random elements, etc.s
- the DoubleSupplier
for generated elementsDoubleStream
static DoubleStream range(double startInclusive, double endExclusive)
DoubleStream
from startInclusive
(inclusive)
to endExclusive
(exclusive) by an incremental step of 1.0.
doubleRange(startInclusive, endExclusive, 1.0);
startInclusive
- the (inclusive) initial valueendExclusive
- the exclusive upper boundDoubleStream
for the range of double
elementsstatic DoubleStream range(double startInclusive, double endExclusive, double step)
DoubleStream
from startInclusive
(inclusive) to endExclusive
(exclusive) by step
. If
startInclusive
is greater than or equal to endExclusive
, an empty stream is returned.
An equivalent sequence of increasing values can be produced
sequentially using a for
loop as follows:
long size = (long) Math.ceil((startInclusive - endExclusive) / step);
long i = 0
for (double v = startInclusive; i < size; i++, v = startInclusive + step * i) {
...
}
startInclusive
- the (inclusive) initial valueendExclusive
- the exclusive upper boundstep
- the difference between consecutive valuesDoubleStream
for tne range of double
elementsIllegalArgumentException
- if step
is less than or equal to
0. is NaN
, or the count of elements in the range would be
greater than Long.MAX_VALUE
boolean isParallel()
true
if this stream would execute in parallel if executed
without further modification otherwise false
S unordered()
This is an intermediate operation.
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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