DoubleStream
public
interface
DoubleStream
implements
BaseStream<Double, DoubleStream>
java.util.stream.DoubleStream 
A sequence of primitive doublevalued elements supporting sequential and parallel
aggregate operations. This is the double
primitive specialization of
Stream
.
The following example illustrates an aggregate operation using
Stream
and DoubleStream
, computing the sum of the weights of the
red widgets:
double sum = widgets.stream()
.filter(w > w.getColor() == RED)
.mapToDouble(w > w.getWeight())
.sum();
See the class documentation for Stream
and the package documentation
for java.util.stream for additional
specification of streams, stream operations, stream pipelines, and
parallelism.
See also:
Summary
Nested classes  

interface 
DoubleStream.Builder
A mutable builder for a 
Public methods  

abstract
boolean

allMatch(DoublePredicate predicate)
Returns whether all elements of this stream match the provided predicate. 
abstract
boolean

anyMatch(DoublePredicate predicate)
Returns whether any elements of this stream match the provided predicate. 
abstract
OptionalDouble

average()
Returns an 
abstract
Stream<Double>

boxed()
Returns a 
static
DoubleStream.Builder

builder()
Returns a builder for a 
abstract
<R>
R

collect(Supplier<R> supplier, ObjDoubleConsumer<R> accumulator, BiConsumer<R, R> combiner)
Performs a mutable reduction operation on the elements of this stream. 
static
DoubleStream

concat(DoubleStream a, DoubleStream b)
Creates a lazily concatenated stream whose elements are all the elements of the first stream followed by all the elements of the second stream. 
abstract
long

count()
Returns the count of elements in this stream. 
abstract
DoubleStream

distinct()
Returns a stream consisting of the distinct elements of this stream. 
static
DoubleStream

empty()
Returns an empty sequential 
abstract
DoubleStream

filter(DoublePredicate predicate)
Returns a stream consisting of the elements of this stream that match the given predicate. 
abstract
OptionalDouble

findAny()
Returns an 
abstract
OptionalDouble

findFirst()
Returns an 
abstract
DoubleStream

flatMap(DoubleFunction<? extends DoubleStream> mapper)
Returns a stream consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element. 
abstract
void

forEach(DoubleConsumer action)
Performs an action for each element of this stream. 
abstract
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 an infinite sequential unordered stream where each element is
generated by the provided 
static
DoubleStream

iterate(double seed, DoubleUnaryOperator f)
Returns an infinite sequential ordered 
abstract
PrimitiveIterator.OfDouble

iterator()
Returns an iterator for the elements of this stream. 
abstract
DoubleStream

limit(long maxSize)
Returns a stream consisting of the elements of this stream, truncated
to be no longer than 
abstract
DoubleStream

map(DoubleUnaryOperator mapper)
Returns a stream consisting of the results of applying the given function to the elements of this stream. 
abstract
IntStream

mapToInt(DoubleToIntFunction mapper)
Returns an 
abstract
LongStream

mapToLong(DoubleToLongFunction mapper)
Returns a 
abstract
<U>
Stream<U>

mapToObj(DoubleFunction<? extends U> mapper)
Returns an objectvalued 
abstract
OptionalDouble

max()
Returns an 
abstract
OptionalDouble

min()
Returns an 
abstract
boolean

noneMatch(DoublePredicate predicate)
Returns whether no elements of this stream match the provided predicate. 
static
DoubleStream

of(double... values)
Returns a sequential ordered stream whose elements are the specified values. 
static
DoubleStream

of(double t)
Returns a sequential 
abstract
DoubleStream

parallel()
Returns an equivalent stream that is parallel. 
abstract
DoubleStream

peek(DoubleConsumer action)
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. 
abstract
OptionalDouble

reduce(DoubleBinaryOperator op)
Performs a reduction on the
elements of this stream, using an
associative accumulation
function, and returns an 
abstract
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. 
abstract
DoubleStream

sequential()
Returns an equivalent stream that is sequential. 
abstract
DoubleStream

skip(long n)
Returns a stream consisting of the remaining elements of this stream
after discarding the first 
abstract
DoubleStream

sorted()
Returns a stream consisting of the elements of this stream in sorted order. 
abstract
Spliterator.OfDouble

spliterator()
Returns a spliterator for the elements of this stream. 
abstract
double

sum()
Returns the sum of elements in this stream. 
abstract
DoubleSummaryStatistics

summaryStatistics()
Returns a 
abstract
double[]

toArray()
Returns an array containing the elements of this stream. 
Inherited methods  

Public methods
allMatch
public abstract boolean allMatch (DoublePredicate predicate)
Returns whether all elements of this stream match the provided predicate.
May not evaluate the predicate on all elements if not necessary for
determining the result. If the stream is empty then true
is
returned and the predicate is not evaluated.
This is a shortcircuiting terminal operation.
API Note:
 This method evaluates the universal quantification of the
predicate over the elements of the stream (for all x P(x)). If the
stream is empty, the quantification is said to be vacuously
satisfied and is always
true
(regardless of P(x)).
Parameters  

predicate 
DoublePredicate : a noninterfering,
stateless
predicate to apply to elements of this stream 
Returns  

boolean 
true if either all elements of the stream match the
provided predicate or the stream is empty, otherwise false

anyMatch
public abstract boolean anyMatch (DoublePredicate predicate)
Returns whether any elements of this stream match the provided
predicate. May not evaluate the predicate on all elements if not
necessary for determining the result. If the stream is empty then
false
is returned and the predicate is not evaluated.
This is a shortcircuiting terminal operation.
API Note:
 This method evaluates the existential quantification of the predicate over the elements of the stream (for some x P(x)).
Parameters  

predicate 
DoublePredicate : a noninterfering,
stateless
predicate to apply to elements of this stream 
Returns  

boolean 
true if any elements of the stream match the provided
predicate, otherwise false

average
public abstract OptionalDouble average ()
Returns an OptionalDouble
describing the arithmetic
mean of elements of this stream, or an empty optional if this
stream is empty.
If any recorded value is a NaN or the sum is at any point a NaN
then the average will be NaN.
The average returned can vary depending upon the order in
which values are recorded.
This method may be implemented using compensated summation or
other technique to reduce the error bound in the numerical sum
used to compute the average.
The average is a special case of a reduction.
This is a terminal operation.
API Note:
 Elements sorted by increasing absolute magnitude tend to yield more accurate results.
Returns  

OptionalDouble 
an OptionalDouble containing the average element of this
stream, or an empty optional if the stream is empty

boxed
public abstract Stream<Double> boxed ()
Returns a Stream
consisting of the elements of this stream,
boxed to Double
.
This is an intermediate operation.
Returns  

Stream<Double> 
a Stream consistent of the elements of this stream,
each boxed to a Double

builder
public static DoubleStream.Builder builder ()
Returns a builder for a DoubleStream
.
Returns  

DoubleStream.Builder 
a stream builder 
collect
public abstract R collect (Supplier<R> supplier, ObjDoubleConsumer<R> accumulator, BiConsumer<R, R> combiner)
Performs a mutable
reduction operation on the elements of this stream. A mutable
reduction is one in which the reduced value is a mutable result container,
such as an 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 = supplier.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.
Parameters  

supplier 
Supplier : 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 
ObjDoubleConsumer : an associative,
noninterfering,
stateless
function for incorporating an additional element into a result 
combiner 
BiConsumer : an associative,
noninterfering,
stateless
function for combining two values, which must be
compatible with the accumulator function 
Returns  

R 
the result of the reduction 
concat
public static DoubleStream concat (DoubleStream a, DoubleStream b)
Creates a lazily concatenated stream whose elements are all the elements of the first stream followed by all the elements of the second stream. The resulting stream is ordered if both of the input streams are ordered, and parallel if either of the input streams is parallel. When the resulting stream is closed, the close handlers for both input streams are invoked.
Implementation Note:
 Use caution when constructing streams from repeated concatenation.
Accessing an element of a deeply concatenated stream can result in deep
call chains, or even
StackOverflowException
.
Parameters  

a 
DoubleStream : the first stream 
b 
DoubleStream : the second stream 
Returns  

DoubleStream 
the concatenation of the two input streams 
count
public abstract long count ()
Returns the count of elements in this stream. This is a special case of a reduction and is equivalent to:
return mapToLong(e > 1L).sum();
This is a terminal operation.
Returns  

long 
the count of elements in this stream 
distinct
public abstract DoubleStream distinct ()
Returns a stream consisting of the distinct elements of this stream. The
elements are compared for equality according to
Double.compare(double, double)
.
This is a stateful intermediate operation.
Returns  

DoubleStream 
the result stream 
empty
public static DoubleStream empty ()
Returns an empty sequential DoubleStream
.
Returns  

DoubleStream 
an empty sequential stream 
filter
public abstract DoubleStream filter (DoublePredicate predicate)
Returns a stream consisting of the elements of this stream that match the given predicate.
This is an intermediate operation.
Parameters  

predicate 
DoublePredicate : a noninterfering,
stateless
predicate to apply to each element to determine if it
should be included 
Returns  

DoubleStream 
the new stream 
findAny
public abstract OptionalDouble findAny ()
Returns an OptionalDouble
describing some element of the stream,
or an empty OptionalDouble
if the stream is empty.
This is a shortcircuiting 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 a stable result
is desired, use findFirst()
instead.)
Returns  

OptionalDouble 
an OptionalDouble describing some element of this stream,
or an empty OptionalDouble if the stream is empty 
See also:
findFirst
public abstract OptionalDouble findFirst ()
Returns an OptionalDouble
describing the first element of this
stream, or an empty OptionalDouble
if the stream is empty. If
the stream has no encounter order, then any element may be returned.
This is a shortcircuiting terminal operation.
Returns  

OptionalDouble 
an OptionalDouble describing the first element of this
stream, or an empty OptionalDouble if the stream is empty

flatMap
public abstract DoubleStream flatMap (DoubleFunction<? extends DoubleStream> mapper)
Returns a stream consisting of the results of replacing each element of
this stream with the contents of a mapped stream produced by applying
the provided mapping function to each element. Each mapped stream is
closed
after its contents
have been placed into this stream. (If a mapped stream is null
an empty stream is used, instead.)
This is an intermediate operation.
Parameters  

mapper 
DoubleFunction : a noninterfering,
stateless
function to apply to each element which produces a
DoubleStream of new values 
Returns  

DoubleStream 
the new stream 
See also:
forEach
public abstract void forEach (DoubleConsumer action)
Performs an action for each element of this stream.
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.
Parameters  

action 
DoubleConsumer : a
noninterfering action to perform on the elements

forEachOrdered
public abstract 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.
This is a terminal operation.
Parameters  

action 
DoubleConsumer : a
noninterfering action to perform on the elements 
See also:
generate
public static DoubleStream generate (DoubleSupplier s)
Returns an infinite sequential unordered stream where each element is
generated by the provided DoubleSupplier
. This is suitable for
generating constant streams, streams of random elements, etc.
Parameters  

s 
DoubleSupplier : the DoubleSupplier for generated elements 
Returns  

DoubleStream 
a new infinite sequential unordered DoubleStream

iterate
public static DoubleStream iterate (double seed, DoubleUnaryOperator f)
Returns an infinite sequential ordered 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
.
Parameters  

seed 
double : the initial element 
f 
DoubleUnaryOperator : a function to be applied to to the previous element to produce
a new element 
Returns  

DoubleStream 
a new sequential DoubleStream

iterator
public abstract PrimitiveIterator.OfDouble iterator ()
Returns an iterator for the elements of this stream.
This is a terminal operation.
Returns  

PrimitiveIterator.OfDouble 
the element iterator for this stream 
limit
public abstract DoubleStream limit (long maxSize)
Returns a stream consisting of the elements of this stream, truncated
to be no longer than maxSize
in length.
This is a shortcircuiting stateful intermediate operation.
API Note:
 While
limit()
is generally a cheap operation on sequential stream pipelines, it can be quite expensive on ordered parallel pipelines, especially for large values ofmaxSize
, sincelimit(n)
is constrained to return not just any n elements, but the first n elements in the encounter order. Using an unordered stream source (such asgenerate(DoubleSupplier)
) or removing the ordering constraint withBaseStream.unordered()
may result in significant speedups oflimit()
in parallel pipelines, if the semantics of your situation permit. If consistency with encounter order is required, and you are experiencing poor performance or memory utilization withlimit()
in parallel pipelines, switching to sequential execution withsequential()
may improve performance.
Parameters  

maxSize 
long : the number of elements the stream should be limited to 
Returns  

DoubleStream 
the new stream 
Throws  

IllegalArgumentException 
if maxSize is negative

map
public abstract DoubleStream map (DoubleUnaryOperator mapper)
Returns a stream consisting of the results of applying the given function to the elements of this stream.
This is an intermediate operation.
Parameters  

mapper 
DoubleUnaryOperator : a noninterfering,
stateless
function to apply to each element 
Returns  

DoubleStream 
the new stream 
mapToInt
public abstract IntStream mapToInt (DoubleToIntFunction mapper)
Returns an IntStream
consisting of the results of applying the
given function to the elements of this stream.
This is an intermediate operation.
Parameters  

mapper 
DoubleToIntFunction : a noninterfering,
stateless
function to apply to each element 
Returns  

IntStream 
the new stream 
mapToLong
public abstract LongStream mapToLong (DoubleToLongFunction mapper)
Returns a LongStream
consisting of the results of applying the
given function to the elements of this stream.
This is an intermediate operation.
Parameters  

mapper 
DoubleToLongFunction : a noninterfering,
stateless
function to apply to each element 
Returns  

LongStream 
the new stream 
mapToObj
public abstract Stream<U> mapToObj (DoubleFunction<? extends U> mapper)
Returns an objectvalued Stream
consisting of the results of
applying the given function to the elements of this stream.
This is an intermediate operation.
Parameters  

mapper 
DoubleFunction : a noninterfering,
stateless
function to apply to each element 
Returns  

Stream<U> 
the new stream 
max
public abstract OptionalDouble max ()
Returns an 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);
This is a terminal operation.
Returns  

OptionalDouble 
an OptionalDouble containing the maximum element of this
stream, or an empty optional if the stream is empty

min
public abstract OptionalDouble min ()
Returns an 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);
This is a terminal operation.
Returns  

OptionalDouble 
an OptionalDouble containing the minimum element of this
stream, or an empty optional if the stream is empty

noneMatch
public abstract boolean noneMatch (DoublePredicate predicate)
Returns whether no elements of this stream match the provided predicate.
May not evaluate the predicate on all elements if not necessary for
determining the result. If the stream is empty then true
is
returned and the predicate is not evaluated.
This is a shortcircuiting terminal operation.
API Note:
 This method evaluates the universal quantification of the
negated predicate over the elements of the stream (for all x ~P(x)). If
the stream is empty, the quantification is said to be vacuously satisfied
and is always
true
, regardless of P(x).
Parameters  

predicate 
DoublePredicate : a noninterfering,
stateless
predicate to apply to elements of this stream 
Returns  

boolean 
true if either no elements of the stream match the
provided predicate or the stream is empty, otherwise false

of
public static DoubleStream of (double... values)
Returns a sequential ordered stream whose elements are the specified values.
Parameters  

values 
double : the elements of the new stream 
Returns  

DoubleStream 
the new stream 
of
public static DoubleStream of (double t)
Returns a sequential DoubleStream
containing a single element.
Parameters  

t 
double : the single element 
Returns  

DoubleStream 
a singleton sequential stream 
parallel
public abstract DoubleStream parallel ()
Returns an equivalent stream that is parallel. May return itself, either because the stream was already parallel, or because the underlying stream state was modified to be parallel.
This is an intermediate operation.
Returns  

DoubleStream 
a parallel stream 
peek
public abstract DoubleStream peek (DoubleConsumer action)
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.
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.
API Note:
 This method exists mainly to support debugging, where you want
to see the elements as they flow past a certain point in a pipeline:
DoubleStream.of(1, 2, 3, 4) .filter(e > e > 2) .peek(e > System.out.println("Filtered value: " + e)) .map(e > e * e) .peek(e > System.out.println("Mapped value: " + e)) .sum();
Parameters  

action 
DoubleConsumer : a
noninterfering action to perform on the elements as
they are consumed from the stream 
Returns  

DoubleStream 
the new stream 
reduce
public abstract 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. This is equivalent to:
boolean foundAny = false;
double result = null;
for (double element : this stream) {
if (!foundAny) {
foundAny = true;
result = element;
}
else
result = accumulator.applyAsDouble(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.
Parameters  

op 
DoubleBinaryOperator : an associative,
noninterfering,
stateless
function for combining two values 
Returns  

OptionalDouble 
the result of the reduction 
See also:
reduce
public abstract 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. This is equivalent to:
double result = identity;
for (double element : this stream)
result = accumulator.applyAsDouble(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.
API Note:
 Sum, min, max, and average are all special cases of reduction.
Summing a stream of numbers can be expressed as:
or more compactly:double sum = numbers.reduce(0, (a, b) > a+b);
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.
Parameters  

identity 
double : the identity value for the accumulating function 
op 
DoubleBinaryOperator : an associative,
noninterfering,
stateless
function for combining two values 
Returns  

double 
the result of the reduction 
sequential
public abstract DoubleStream sequential ()
Returns an equivalent stream that is sequential. May return itself, either because the stream was already sequential, or because the underlying stream state was modified to be sequential.
This is an intermediate operation.
Returns  

DoubleStream 
a sequential stream 
skip
public abstract DoubleStream skip (long n)
Returns a stream consisting of the remaining elements of this stream
after discarding the first n
elements of the stream.
If this stream contains fewer than n
elements then an
empty stream will be returned.
This is a stateful intermediate operation.
API Note:
 While
skip()
is generally a cheap operation on sequential stream pipelines, it can be quite expensive on ordered parallel pipelines, especially for large values ofn
, sinceskip(n)
is constrained to skip not just any n elements, but the first n elements in the encounter order. Using an unordered stream source (such asgenerate(DoubleSupplier)
) or removing the ordering constraint withBaseStream.unordered()
may result in significant speedups ofskip()
in parallel pipelines, if the semantics of your situation permit. If consistency with encounter order is required, and you are experiencing poor performance or memory utilization withskip()
in parallel pipelines, switching to sequential execution withsequential()
may improve performance.
Parameters  

n 
long : the number of leading elements to skip 
Returns  

DoubleStream 
the new stream 
Throws  

IllegalArgumentException 
if n is negative

sorted
public abstract DoubleStream sorted ()
Returns a stream consisting of the elements of this stream in sorted
order. The elements are compared for equality according to
Double.compare(double, double)
.
This is a stateful intermediate operation.
Returns  

DoubleStream 
the result stream 
spliterator
public abstract Spliterator.OfDouble spliterator ()
Returns a spliterator for the elements of this stream.
This is a terminal operation.
Returns  

Spliterator.OfDouble 
the element spliterator for this stream 
sum
public abstract double sum ()
Returns the sum of elements in this stream. Summation is a special case of a reduction. If floatingpoint summation were exact, this method would be equivalent to:
return reduce(0, Double::sum);
However, since floatingpoint summation is not exact, the above
code is not necessarily equivalent to the summation computation
done by this method.
If any stream element is a NaN or the sum is at any point a NaN
then the sum will be NaN.
The value of a floatingpoint sum is a function both
of the input values as well as the order of addition
operations. The order of addition operations of this method is
intentionally not defined to allow for implementation
flexibility to improve the speed and accuracy of the computed
result.
In particular, this method may be implemented using compensated
summation or other technique to reduce the error bound in the
numerical sum compared to a simple summation of double
values.
This is a terminal operation.
API Note:
 Elements sorted by increasing absolute magnitude tend to yield more accurate results.
Returns  

double 
the sum of elements in this stream 
summaryStatistics
public abstract DoubleSummaryStatistics summaryStatistics ()
Returns a DoubleSummaryStatistics
describing various summary data
about the elements of this stream. This is a special
case of a reduction.
This is a terminal operation.
Returns  

DoubleSummaryStatistics 
a DoubleSummaryStatistics describing various summary data
about the elements of this stream

toArray
public abstract double[] toArray ()
Returns an array containing the elements of this stream.
This is a terminal operation.
Returns  

double[] 
an array containing the elements of this stream 