DoubleStream

See also:

• Stream
• java.util.stream

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 short-circuiting terminal operation.

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 short-circuiting terminal operation.

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.

The computed average can vary numerically and have the special case behavior as computing the sum; see sum() for details.

The average is a special case of a reduction.

This is a terminal operation.

boxed

public abstract Stream<Double> boxed ()

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

This is an intermediate operation.

builder

public static DoubleStream.Builder builder ()

Returns a builder for a DoubleStream.

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.

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.

This method operates on the two input streams and binds each stream to its source. As a result subsequent modifications to an input stream source may not be reflected in the concatenated stream result.

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.

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.

dropWhile

public DoubleStream dropWhile (DoublePredicate predicate)

Returns, if this stream is ordered, a stream consisting of the remaining elements of this stream after dropping the longest prefix of elements that match the given predicate. Otherwise returns, if this stream is unordered, a stream consisting of the remaining elements of this stream after dropping a subset of elements that match the given predicate.

If this stream is ordered then the longest prefix is a contiguous sequence of elements of this stream that match the given predicate. The first element of the sequence is the first element of this stream, and the element immediately following the last element of the sequence does not match the given predicate.

If this stream is unordered, and some (but not all) elements of this stream match the given predicate, then the behavior of this operation is nondeterministic; it is free to drop any subset of matching elements (which includes the empty set).

Independent of whether this stream is ordered or unordered if all elements of this stream match the given predicate then this operation drops all elements (the result is an empty stream), or if no elements of the stream match the given predicate then no elements are dropped (the result is the same as the input).

This is a stateful intermediate operation.

empty

public static DoubleStream empty ()

Returns an empty sequential DoubleStream.

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.

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 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.)

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 short-circuiting terminal operation.

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.

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.

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.

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.

iterate

public static DoubleStream iterate (double seed, 
                DoublePredicate hasNext, 
                DoubleUnaryOperator next)

Returns a sequential ordered DoubleStream produced by iterative application of the given next function to an initial element, conditioned on satisfying the given hasNext predicate. The stream terminates as soon as the hasNext predicate returns false.

DoubleStream.iterate should produce the same sequence of elements as produced by the corresponding for-loop:

for (double index=seed; hasNext.test(index); index = next.applyAsDouble(index)) {
         ...
     }
 

The resulting sequence may be empty if the hasNext predicate does not hold on the seed value. Otherwise the first element will be the supplied seed value, the next element (if present) will be the result of applying the next function to the seed value, and so on iteratively until the hasNext predicate indicates that the stream should terminate.

The action of applying the hasNext predicate to an element happens-before the action of applying the next function to that element. The action of applying the next function for one element happens-before the action of applying the hasNext predicate for subsequent elements. For any given element an action may be performed in whatever thread the library chooses.

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.

The action of applying f for one element happens-before the action of applying f for subsequent elements. For any given element the action may be performed in whatever thread the library chooses.

iterator

public abstract PrimitiveIterator.OfDouble iterator ()

Returns an iterator for the elements of this stream.

This is a terminal operation.

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 short-circuiting stateful intermediate operation.

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.

mapMulti

public DoubleStream mapMulti (DoubleStream.DoubleMapMultiConsumer mapper)

Returns a stream consisting of the results of replacing each element of this stream with multiple elements, specifically zero or more elements. Replacement is performed by applying the provided mapping function to each element in conjunction with a consumer argument that accepts replacement elements. The mapping function calls the consumer zero or more times to provide the replacement elements.

This is an intermediate operation.

If the consumer argument is used outside the scope of its application to the mapping function, the results are undefined.

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.

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.

mapToObj

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.

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.

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.

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 short-circuiting terminal operation.

of

public static DoubleStream of (double... values)

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

of

public static DoubleStream of (double t)

Returns a sequential DoubleStream containing a single element.

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.

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.

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();
 

The accumulator function must be an associative function.

This is a terminal operation.

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;
 

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.

See also:

• sum()
• min()
• max()
• average()

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.

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.

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.

spliterator

public abstract Spliterator.OfDouble spliterator ()

Returns a spliterator for the elements of this stream.

This is a terminal operation.

sum

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);
 

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. Because of the unspecified order of operations and the possibility of using differing summation schemes, the output of this method may vary on the same input elements.

Various conditions can result in a non-finite sum being computed. This can occur even if the all the elements being summed are finite. If any element is non-finite, the sum will be non-finite:

• If any element is a NaN, then the final sum will be NaN.
• If the elements contain one or more infinities, the sum will be infinite or NaN.
  • If the elements contain infinities of opposite sign, the sum will be NaN.
  • If the elements contain infinities of one sign and an intermediate sum overflows to an infinity of the opposite sign, the sum may be NaN.

This is a terminal operation.

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.

takeWhile

public DoubleStream takeWhile (DoublePredicate predicate)

Returns, if this stream is ordered, a stream consisting of the longest prefix of elements taken from this stream that match the given predicate. Otherwise returns, if this stream is unordered, a stream consisting of a subset of elements taken from this stream that match the given predicate.

If this stream is ordered then the longest prefix is a contiguous sequence of elements of this stream that match the given predicate. The first element of the sequence is the first element of this stream, and the element immediately following the last element of the sequence does not match the given predicate.

If this stream is unordered, and some (but not all) elements of this stream match the given predicate, then the behavior of this operation is nondeterministic; it is free to take any subset of matching elements (which includes the empty set).

Independent of whether this stream is ordered or unordered if all elements of this stream match the given predicate then this operation takes all elements (the result is the same as the input), or if no elements of the stream match the given predicate then no elements are taken (the result is an empty stream).

This is a short-circuiting stateful intermediate operation.

toArray

public abstract double[] toArray ()

Returns an array containing the elements of this stream.

This is a terminal operation.