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 * {@link #forEach(DoubleConsumer)}), are explicitly nondeterministic for parallel * execution of stream pipelines. * *
Unless otherwise noted, passing a {@code null} argument to any stream
* method may result in a {@link NullPointerException}.
*
* @apiNote
* Streams are not data structures; they do not manage the storage for their
* elements, nor do they support access to individual elements. However,
* you can use the {@link #iterator()} or {@link #spliterator()} operations to
* perform a controlled traversal.
*
* @since 1.8
* @see java.util.stream
*/
public interface DoubleStream extends BaseStream This is an intermediate
* operation.
*
* @param predicate a
* non-interfering, stateless predicate to apply to
* each element to determine if it should be included
* @return the new stream
*/
DoubleStream filter(DoublePredicate predicate);
/**
* Returns a stream consisting of the results of applying the given
* function to the elements of this stream.
*
* This is an intermediate
* operation.
*
* @param mapper a
* non-interfering, stateless function to apply to
* each element
* @return the new stream
*/
DoubleStream map(DoubleUnaryOperator mapper);
/**
* Returns an object-valued {@code Stream} consisting of the results of
* applying the given function to the elements of this stream.
*
* This is an
* intermediate operation.
*
* @param the element type of the new stream
* @param mapper a
* non-interfering, stateless function to apply to each
* element
* @return the new stream
*/
Stream mapToObj(DoubleFunction mapper);
/**
* Returns an {@code IntStream} consisting of the results of applying the
* given function to the elements of this stream.
*
* This is an intermediate
* operation.
*
* @param mapper a
* non-interfering, stateless function to apply to each
* element
* @return the new stream
*/
IntStream mapToInt(DoubleToIntFunction mapper);
/**
* Returns a {@code LongStream} consisting of the results of applying the
* given function to the elements of this stream.
*
* This is an intermediate
* operation.
*
* @param mapper a
* non-interfering, stateless function to apply to each
* element
* @return the new stream
*/
LongStream mapToLong(DoubleToLongFunction 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.
*
* This is an intermediate
* operation.
*
* @apiNote
* The {@code 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 {@code 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:
* This is a stateful
* intermediate operation.
*
* @return the result stream
*/
DoubleStream distinct();
/**
* Returns a stream consisting of the elements of this stream in sorted
* order. The elements are compared for equality according to
* {@link java.lang.Double#compare(double, double)}.
*
* This is a stateful
* intermediate operation.
*
* @return the result stream
*/
DoubleStream sorted();
/**
* 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.
*
* @apiNote This method exists mainly to support debugging, where you want
* to see the elements as they flow past a certain point in a pipeline:
* This is a short-circuiting
* stateful intermediate operation.
*
* @param maxSize the number of elements the stream should be limited to
* @return the new stream
* @throws IllegalArgumentException if {@code maxSize} is negative
*/
DoubleStream limit(long maxSize);
/**
* Returns a stream consisting of the remaining elements of this stream
* after indexing {@code startInclusive} elements into the stream. If the
* {@code startInclusive} index lies past the end of this stream then an
* empty stream will be returned.
*
* This is a stateful
* intermediate operation.
*
* @param startInclusive the number of leading elements to skip
* @return the new stream
* @throws IllegalArgumentException if {@code startInclusive} is negative
*/
DoubleStream substream(long startInclusive);
/**
* Returns a stream consisting of the remaining elements of this stream
* after indexing {@code startInclusive} elements into the stream and
* truncated to contain no more than {@code endExclusive - startInclusive}
* elements. If the {@code startInclusive} index lies past the end
* of this stream then an empty stream will be returned.
*
* This is a short-circuiting
* stateful intermediate operation.
*
* @param startInclusive the starting position of the substream, inclusive
* @param endExclusive the ending position of the substream, exclusive
* @return the new stream
* @throws IllegalArgumentException if {@code startInclusive} or
* {@code endExclusive} is negative or {@code startInclusive} is greater
* than {@code endExclusive}
*/
DoubleStream substream(long startInclusive, long endExclusive);
/**
* 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.
*
* @param action a
* non-interfering action to perform on the elements
*/
void forEach(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.
*
* @param action a
* non-interfering action to perform on the elements
* @see #forEach(DoubleConsumer)
*/
void forEachOrdered(DoubleConsumer action);
/**
* Returns an array containing the elements of this stream.
*
* This is a terminal
* operation.
*
* @return an array containing the elements of this stream
*/
double[] toArray();
/**
* 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:
* The {@code identity} value must be an identity for the accumulator
* function. This means that for all {@code x},
* {@code accumulator.apply(identity, x)} is equal to {@code x}.
* The {@code accumulator} function must be an
* associative function.
*
* This is a terminal
* operation.
*
* @apiNote Sum, min, max, and average are all special cases of reduction.
* Summing a stream of numbers can be expressed as:
* 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.
*
* @param identity the identity value for the accumulating function
* @param op an associative
* non-interfering,
* stateless function for combining two values
* @return the result of the reduction
* @see #sum()
* @see #min()
* @see #max()
* @see #average()
*/
double reduce(double identity, DoubleBinaryOperator op);
/**
* Performs a reduction on the
* elements of this stream, using an
* associative accumulation
* function, and returns an {@code OptionalDouble} describing the reduced
* value, if any. This is equivalent to:
* The {@code accumulator} function must be an
* associative function.
*
* This is a terminal
* operation.
*
* @param op an associative
* non-interfering,
* stateless function for combining two values
* @return the result of the reduction
* @see #reduce(double, DoubleBinaryOperator)
*/
OptionalDouble reduce(DoubleBinaryOperator op);
/**
* Performs a mutable
* reduction operation on the elements of this stream. A mutable
* reduction is one in which the reduced value is a mutable value holder,
* such as an {@code ArrayList}, and elements are incorporated by updating
* the state of the result, rather than by replacing the result. This
* produces a result equivalent to:
* Like {@link #reduce(double, DoubleBinaryOperator)}, {@code collect}
* operations can be parallelized without requiring additional
* synchronization.
*
* This is a terminal
* operation.
*
* @param This is a terminal operation.
*
* @return the count of elements in this stream
*/
long count();
/**
* Returns an {@code OptionalDouble} describing the arithmetic mean 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 {@code NaN} or the sum is at any point a {@code NaN} then the average
* will be {@code NaN}. This is a special case of a
* reduction.
*
* @return an {@code OptionalDouble} containing the average element of this
* stream, or an empty optional if the stream is empty
*/
OptionalDouble average();
/**
* Returns a {@code DoubleSummaryStatistics} describing various summary data
* about the elements of this stream. This is a special
* case of a reduction.
*
* @return a {@code DoubleSummaryStatistics} describing various summary data
* about the elements of this stream
*/
DoubleSummaryStatistics summaryStatistics();
/**
* 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.
*
* This is a short-circuiting
* terminal operation.
*
* @param predicate a non-interfering,
* stateless predicate to apply to elements of this
* stream
* @return {@code true} if any elements of the stream match the provided
* predicate otherwise {@code false}
*/
boolean anyMatch(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.
*
* This is a short-circuiting
* terminal operation.
*
* @param predicate a non-interfering,
* stateless predicate to apply to elements of this
* stream
* @return {@code true} if all elements of the stream match the provided
* predicate otherwise {@code false}
*/
boolean allMatch(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.
*
* This is a short-circuiting
* terminal operation.
*
* @param predicate a non-interfering,
* stateless predicate to apply to elements of this
* stream
* @return {@code true} if no elements of the stream match the provided
* predicate otherwise {@code false}
*/
boolean noneMatch(DoublePredicate predicate);
/**
* Returns an {@link OptionalDouble} describing the first element of this
* stream (in the encounter order), or an empty {@code 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.
*
* @return an {@code OptionalDouble} describing the first element of this
* stream, or an empty {@code OptionalDouble} if the stream is empty
*/
OptionalDouble findFirst();
/**
* Returns an {@link OptionalDouble} describing some element of the stream,
* or an empty {@code 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 {@link #findFirst()} instead.)
*
* @return an {@code OptionalDouble} describing some element of this stream,
* or an empty {@code OptionalDouble} if the stream is empty
* @see #findFirst()
*/
OptionalDouble findAny();
/**
* Returns a {@code Stream} consisting of the elements of this stream,
* boxed to {@code Double}.
*
* @return a {@code Stream} consistent of the elements of this stream,
* each boxed to a {@code Double}
*/
Stream The first element (position {@code 0}) in the {@code DoubleStream}
* will be the provided {@code seed}. For {@code n > 0}, the element at
* position {@code n}, will be the result of applying the function {@code f}
* to the element at position {@code n - 1}.
*
* @param seed the initial element
* @param f a function to be applied to to the previous element to produce
* a new element
* @return a new sequential {@code DoubleStream}
*/
public static DoubleStream iterate(final double seed, final DoubleUnaryOperator f) {
Objects.requireNonNull(f);
final PrimitiveIterator.OfDouble iterator = new PrimitiveIterator.OfDouble() {
double t = seed;
@Override
public boolean hasNext() {
return true;
}
@Override
public double nextDouble() {
double v = t;
t = f.applyAsDouble(t);
return v;
}
};
return StreamSupport.doubleStream(Spliterators.spliteratorUnknownSize(
iterator,
Spliterator.ORDERED | Spliterator.IMMUTABLE | Spliterator.NONNULL), false);
}
/**
* Returns a sequential {@code DoubleStream} where each element is
* generated by an {@code DoubleSupplier}. This is suitable for generating
* constant streams, streams of random elements, etc.
*
* @param s the {@code DoubleSupplier} for generated elements
* @return a new sequential {@code DoubleStream}
*/
public static DoubleStream generate(DoubleSupplier s) {
Objects.requireNonNull(s);
return StreamSupport.doubleStream(
new StreamSpliterators.InfiniteSupplyingSpliterator.OfDouble(Long.MAX_VALUE, s), false);
}
/**
* Creates a lazy concatenated {@code DoubleStream} whose elements are all the
* elements of a first {@code DoubleStream} succeeded by all the elements of the
* second {@code DoubleStream}. 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.
*
* @param a the first stream
* @param b the second stream to concatenate on to end of the first stream
* @return the concatenation of the two streams
*/
public static DoubleStream concat(DoubleStream a, DoubleStream b) {
Objects.requireNonNull(a);
Objects.requireNonNull(b);
Spliterator.OfDouble split = new Streams.ConcatSpliterator.OfDouble(
a.spliterator(), b.spliterator());
DoubleStream stream = StreamSupport.doubleStream(split, a.isParallel() || b.isParallel());
return stream.onClose(Streams.composedClose(a, b));
}
/**
* A mutable builder for a {@code DoubleStream}.
*
* A stream builder has a lifecycle, where it starts in a building
* phase, during which elements can be added, and then transitions to a
* built phase, after which elements may not be added. The built phase
* begins when the {@link #build()} method is called, which creates an
* ordered stream whose elements are the elements that were added to the
* stream builder, in the order they were added.
*
* @see DoubleStream#builder()
* @since 1.8
*/
public interface Builder extends DoubleConsumer {
/**
* Adds an element to the stream being built.
*
* @throws IllegalStateException if the builder has already transitioned
* to the built state
*/
@Override
void accept(double t);
/**
* Adds an element to the stream being built.
*
* @implSpec
* The default implementation behaves as if:
* {@code
* orderStream.flatMap(order -> order.getLineItems().stream())...
* }
*
* @param mapper a
* non-interfering, stateless function to apply to
* each element which produces an {@code DoubleStream} of new
* values
* @return the new stream
* @see Stream#flatMap(Function)
*/
DoubleStream flatMap(DoubleFunction mapper);
/**
* Returns a stream consisting of the distinct elements of this stream. The
* elements are compared for equality according to
* {@link java.lang.Double#compare(double, double)}.
*
* {@code
* 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());
* }
*
* @param consumer a
* non-interfering action to perform on the elements as
* they are consumed from the stream
* @return the new stream
*/
DoubleStream peek(DoubleConsumer consumer);
/**
* Returns a stream consisting of the elements of this stream, truncated
* to be no longer than {@code maxSize} in length.
*
* {@code
* double result = identity;
* for (double element : this stream)
* result = accumulator.apply(result, element)
* return result;
* }
*
* but is not constrained to execute sequentially.
*
* {@code
* double sum = numbers.reduce(0, (a, b) -> a+b);
* }
*
* or more compactly:
*
* {@code
* double sum = numbers.reduce(0, Double::sum);
* }
*
* {@code
* 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.
*
* {@code
* R result = resultFactory.get();
* for (double element : this stream)
* accumulator.accept(result, element);
* return result;
* }
*
* {@code
* return reduce(0, Double::sum);
* }
*
* @return the sum of elements in this stream
*/
double sum();
/**
* Returns an {@code OptionalDouble} describing the minimum element of this
* stream, or an empty OptionalDouble if this stream is empty. The minimum
* element will be {@code 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:
* {@code
* return reduce(Double::min);
* }
*
* @return an {@code OptionalDouble} containing the minimum element of this
* stream, or an empty optional if the stream is empty
*/
OptionalDouble min();
/**
* Returns an {@code OptionalDouble} describing the maximum element of this
* stream, or an empty OptionalDouble if this stream is empty. The maximum
* element will be {@code 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:
* {@code
* return reduce(Double::max);
* }
*
* @return an {@code OptionalDouble} containing the maximum element of this
* stream, or an empty optional if the stream is empty
*/
OptionalDouble max();
/**
* Returns the count of elements in this stream. This is a special case of
* a reduction and is
* equivalent to:
* {@code
* return mapToLong(e -> 1L).sum();
* }
*
* {@code
* accept(t)
* return this;
* }
*
* @param t the element to add
* @return {@code this} builder
* @throws IllegalStateException if the builder has already transitioned
* to the built state
*/
default Builder add(double t) {
accept(t);
return this;
}
/**
* Builds the stream, transitioning this builder to the built state.
* An {@code IllegalStateException} is thrown if there are further
* attempts to operate on the builder after it has entered the built
* state.
*
* @return the built stream
* @throws IllegalStateException if the builder has already transitioned
* to the built state
*/
DoubleStream build();
}
}