DoubleStream

public interface DoubleStream implements BaseStream<Double, DoubleStream>

A sequence of primitive double-valued 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

Nested Class Summary

interface DoubleStream.Builder A mutable builder for a DoubleStream. 

Public Method Summary

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 OptionalDouble describing the arithmetic mean of elements of this stream, or an empty optional if this stream is empty.
abstract Stream<Double>
boxed()
Returns a Stream consisting of the elements of this stream, boxed to Double.
static DoubleStream.Builder
builder()
Returns a builder for a DoubleStream.
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 DoubleStream.
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 OptionalDouble describing some element of the stream, or an empty OptionalDouble if the stream is empty.
abstract OptionalDouble
findFirst()
Returns an OptionalDouble describing the first element of this stream, or an empty OptionalDouble if the stream is empty.
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 DoubleSupplier.
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.
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 maxSize in length.
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 IntStream consisting of the results of applying the given function to the elements of this stream.
abstract LongStream
mapToLong(DoubleToLongFunction mapper)
Returns a LongStream consisting of the results of applying the given function to the elements of this stream.
abstract <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.
abstract OptionalDouble
max()
Returns an OptionalDouble describing the maximum element of this stream, or an empty OptionalDouble if this stream is empty.
abstract OptionalDouble
min()
Returns an OptionalDouble describing the minimum element of this stream, or an empty OptionalDouble if this stream is empty.
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 DoubleStream containing a single element.
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 OptionalDouble describing the reduced value, if any.
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 n elements of the stream.
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 DoubleSummaryStatistics describing various summary data about the elements of this stream.
abstract double[]
toArray()
Returns an array containing the elements of this stream.

Inherited Method Summary

Public Methods

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 short-circuiting terminal operation.

Parameters
predicate a non-interfering, stateless predicate to apply to elements of this stream
Returns
  • true if either all elements of the stream match the provided predicate or the stream is empty, otherwise false

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 short-circuiting terminal operation.

Parameters
predicate a non-interfering, stateless predicate to apply to elements of this stream
Returns
  • true if any elements of the stream match the provided predicate, otherwise false

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.

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

public abstract Stream<Double> boxed ()

Returns a Stream consisting of the elements of this stream, boxed to Double.

This is an intermediate operation.

Returns
  • a Stream consistent of the elements of this stream, each boxed to a Double

public static DoubleStream.Builder builder ()

Returns a builder for a DoubleStream.

Returns
  • a stream builder

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 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 result
combiner an associative, non-interfering, stateless function for combining two values, which must be compatible with the accumulator function
Returns
  • the result of the reduction
See Also

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.

Parameters
a the first stream
b the second stream
Returns
  • the concatenation of the two input streams

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
  • the count of elements in this stream

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
  • the result stream

public static DoubleStream empty ()

Returns an empty sequential DoubleStream.

Returns
  • an empty sequential stream

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 a non-interfering, stateless predicate to apply to each element to determine if it should be included
Returns
  • the new stream

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 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 a stable result is desired, use findFirst() instead.)

Returns
  • an OptionalDouble describing some element of this stream, or an empty OptionalDouble if the stream is empty
See Also

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 short-circuiting terminal operation.

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

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 a non-interfering, stateless function to apply to each element which produces a DoubleStream of new values
Returns
  • the new stream
See Also

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 a non-interfering action to perform on the elements

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 a non-interfering action to perform on the elements
See Also

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 the DoubleSupplier for generated elements
Returns
  • a new infinite sequential unordered DoubleStream

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 the initial element
f a function to be applied to to the previous element to produce a new element
Returns
  • a new sequential DoubleStream

public abstract PrimitiveIterator.OfDouble iterator ()

Returns an iterator for the elements of this stream.

This is a terminal operation.

Returns
  • the element iterator for this stream

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 short-circuiting stateful intermediate operation.

Parameters
maxSize the number of elements the stream should be limited to
Returns
  • the new stream
Throws
IllegalArgumentException if maxSize is negative

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 a non-interfering, stateless function to apply to each element
Returns
  • the new stream

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 a non-interfering, stateless function to apply to each element
Returns
  • the new stream

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 a non-interfering, stateless function to apply to each element
Returns
  • the new stream

public abstract 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.

This is an intermediate operation.

Parameters
mapper a non-interfering, stateless function to apply to each element
Returns
  • the new stream

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

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

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 short-circuiting terminal operation.

Parameters
predicate a non-interfering, stateless predicate to apply to elements of this stream
Returns
  • true if either no elements of the stream match the provided predicate or the stream is empty, otherwise false

public static DoubleStream of (double... values)

Returns a sequential ordered stream whose elements are the specified values.

Parameters
values the elements of the new stream
Returns
  • the new stream

public static DoubleStream of (double t)

Returns a sequential DoubleStream containing a single element.

Parameters
t the single element
Returns
  • a singleton sequential stream

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
  • a parallel stream

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.

Parameters
action a non-interfering action to perform on the elements as they are consumed from the stream
Returns
  • the new stream

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 an associative, non-interfering, stateless function for combining two values
Returns
  • the result of the reduction
See Also

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.

Parameters
identity the identity value for the accumulating function
op an associative, non-interfering, stateless function for combining two values
Returns
  • the result of the reduction
See Also

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
  • a sequential stream

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.

Parameters
n the number of leading elements to skip
Returns
  • the new stream
Throws
IllegalArgumentException if n is negative

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
  • the result stream

public abstract Spliterator.OfDouble spliterator ()

Returns a spliterator for the elements of this stream.

This is a terminal operation.

Returns
  • the element spliterator for this stream

public abstract double sum ()

Returns the sum of elements in this stream. Summation is a special case of a reduction. If floating-point summation were exact, this method would be equivalent to: 

return reduce(0, Double::sum);
However, since floating-point 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 floating-point 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.

Returns
  • the sum of elements in this stream

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

public abstract double[] toArray ()

Returns an array containing the elements of this stream.

This is a terminal operation.

Returns
  • an array containing the elements of this stream