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package java.util.stream;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Arrays;
import java.util.Collection;
import java.util.DoubleSummaryStatistics;
import java.util.Objects;
import java.util.OptionalDouble;
import java.util.PrimitiveIterator;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.BiConsumer;
import java.util.function.DoubleBinaryOperator;
import java.util.function.DoubleConsumer;
import java.util.function.DoubleFunction;
import java.util.function.DoublePredicate;
import java.util.function.DoubleSupplier;
import java.util.function.DoubleToIntFunction;
import java.util.function.DoubleToLongFunction;
import java.util.function.DoubleUnaryOperator;
import java.util.function.Function;
import java.util.function.ObjDoubleConsumer;
import java.util.function.Supplier;
/**
* A sequence of elements supporting sequential and parallel aggregate
* operations. The following example illustrates an aggregate operation using
* {@link Stream} and {@link DoubleStream}:
*
* <pre>{@code
* double sum = widgets.stream()
* .filter(w -> w.getColor() == RED)
* .mapToDouble(w -> w.getWeight())
* .sum();
* }</pre>
*
* In this example, {@code widgets} is a {@code Collection<Widget>}. We create
* a stream of {@code Widget} objects via {@link Collection#stream Collection.stream()},
* filter it to produce a stream containing only the red widgets, and then
* transform it into a stream of {@code double} values representing the weight of
* each red widget. Then this stream is summed to produce a total weight.
*
* <p>To perform a computation, stream
* <a href="package-summary.html#StreamOps">operations</a> are composed into a
* <em>stream pipeline</em>. A stream pipeline consists of a source (which
* might be an array, a collection, a generator function, an IO channel,
* etc), zero or more <em>intermediate operations</em> (which transform a
* stream into another stream, such as {@link DoubleStream#filter(DoublePredicate)}), and a
* <em>terminal operation</em> (which produces a result or side-effect, such
* as {@link DoubleStream#sum()} or {@link DoubleStream#forEach(DoubleConsumer)}.
* Streams are lazy; computation on the source data is only performed when the
* terminal operation is initiated, and source elements are consumed only
* as needed.
*
* <p>Collections and streams, while bearing some superficial similarities,
* have different goals. Collections are primarily concerned with the efficient
* management of, and access to, their elements. By contrast, streams do not
* provide a means to directly access or manipulate their elements, and are
* instead concerned with declaratively describing their source and the
* computational operations which will be performed in aggregate on that source.
* However, if the provided stream operations do not offer the desired
* functionality, the {@link #iterator()} and {@link #spliterator()} operations
* can be used to perform a controlled traversal.
*
* <p>A stream pipeline, like the "widgets" example above, can be viewed as
* a <em>query</em> on the stream source. Unless the source was explicitly
* designed for concurrent modification (such as a {@link ConcurrentHashMap}),
* unpredictable or erroneous behavior may result from modifying the stream
* source while it is being queried.
*
* <p>Most stream operations accept parameters that describe user-specified
* behavior, such as the lambda expression {@code w -> w.getWeight()} passed to
* {@code mapToDouble} in the example above. Such parameters are always instances
* of a <a href="../function/package-summary.html">functional interface</a> such
* as {@link java.util.function.Function}, and are often lambda expressions or
* method references. These parameters can never be null, should not modify the
* stream source, and should be
* <a href="package-summary.html#NonInterference">effectively stateless</a>
* (their result should not depend on any state that might change during
* execution of the stream pipeline.)
*
* <p>A stream should be operated on (invoking an intermediate or terminal stream
* operation) only once. This rules out, for example, "forked" streams, where
* the same source feeds two or more pipelines, or multiple traversals of the
* same stream. A stream implementation may throw {@link IllegalStateException}
* if it detects that the stream is being reused. However, since some stream
* operations may return their receiver rather than a new stream object, it may
* not be possible to detect reuse in all cases.
*
* <p>Streams have a {@link #close()} method and implement {@link AutoCloseable},
* but nearly all stream instances do not actually need to be closed after use.
* Generally, only streams whose source is an IO channel (such as those returned
* by {@link Files#lines(Path, Charset)}) will require closing. Most streams
* are backed by collections, arrays, or generating functions, which require no
* special resource management. (If a stream does require closing, it can be
* declared as a resource in a {@code try}-with-resources statement.)
*
* <p>Stream pipelines may execute either sequentially or in
* <a href="package-summary.html#Parallelism">parallel</a>. This
* execution mode is a property of the stream. Streams are created
* with an initial choice of sequential or parallel execution. (For example,
* {@link Collection#stream() Collection.stream()} creates a sequential stream,
* and {@link Collection#parallelStream() Collection.parallelStream()} creates
* a parallel one.) This choice of execution mode may be modified by the
* {@link #sequential()} or {@link #parallel()} methods, and may be queried with
* the {@link #isParallel()} method.
*
* @since 1.8
* @see <a href="package-summary.html">java.util.stream</a>
*/
public interface DoubleStream extends BaseStream<Double, DoubleStream> {
/**
* Returns a stream consisting of the elements of this stream that match
* the given predicate.
*
* <p>This is an <a href="package-summary.html#StreamOps">intermediate
* operation</a>.
*
* @param predicate a <a href="package-summary.html#NonInterference">
* non-interfering, stateless</a> 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.
*
* <p>This is an <a href="package-summary.html#StreamOps">intermediate
* operation</a>.
*
* @param mapper a <a href="package-summary.html#NonInterference">
* non-interfering, stateless</a> 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.
*
* <p>This is an <a href="package-summary.html#StreamOps">
* intermediate operation</a>.
*
* @param <U> the element type of the new stream
* @param mapper a <a href="package-summary.html#NonInterference">
* non-interfering, stateless</a> function to apply to each
* element
* @return the new stream
*/
<U> Stream<U> mapToObj(DoubleFunction<? extends U> mapper);
/**
* Returns an {@code IntStream} consisting of the results of applying the
* given function to the elements of this stream.
*
* <p>This is an <a href="package-summary.html#StreamOps">intermediate
* operation</a>.
*
* @param mapper a <a href="package-summary.html#NonInterference">
* non-interfering, stateless</a> 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.
*
* <p>This is an <a href="package-summary.html#StreamOps">intermediate
* operation</a>.
*
* @param mapper a <a href="package-summary.html#NonInterference">
* non-interfering, stateless</a> 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. (If the result of the mapping
* function is {@code null}, this is treated as if the result was an empty
* stream.)
*
* <p>This is an <a href="package-summary.html#StreamOps">intermediate
* operation</a>.
*
* @param mapper a <a href="package-summary.html#NonInterference">
* non-interfering, stateless</a> 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<? extends DoubleStream> 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)}.
*
* <p>This is a <a href="package-summary.html#StreamOps">stateful
* intermediate operation</a>.
*
* @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)}.
*
* <p>This is a <a href="package-summary.html#StreamOps">stateful
* intermediate operation</a>.
*
* @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.
*
* <p>This is an <a href="package-summary.html#StreamOps">intermediate
* operation</a>.
*
* <p>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:
* <pre>{@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());
* }</pre>
*
* @param action a <a href="package-summary.html#NonInterference">
* non-interfering</a> action to perform on the elements as
* they are consumed from the stream
* @return the new stream
*/
DoubleStream peek(DoubleConsumer action);
/**
* Returns a stream consisting of the elements of this stream, truncated
* to be no longer than {@code maxSize} in length.
*
* <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
* stateful intermediate operation</a>.
*
* @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 discarding the first {@code startInclusive} elements of the stream.
* If this stream contains fewer than {@code startInclusive} elements then an
* empty stream will be returned.
*
* <p>This is a <a href="package-summary.html#StreamOps">stateful
* intermediate operation</a>.
*
* @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 discarding the first {@code startInclusive} elements and truncating
* the result to be no longer than {@code endExclusive - startInclusive}
* elements in length. If this stream contains fewer than
* {@code startInclusive} elements then an empty stream will be returned.
*
* <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
* stateful intermediate operation</a>.
*
* @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.
*
* <p>This is a <a href="package-summary.html#StreamOps">terminal
* operation</a>.
*
* <p>For parallel stream pipelines, this operation does <em>not</em>
* 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 <a href="package-summary.html#NonInterference">
* non-interfering</a> 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.
*
* <p>This is a <a href="package-summary.html#StreamOps">terminal
* operation</a>.
*
* @param action a <a href="package-summary.html#NonInterference">
* non-interfering</a> action to perform on the elements
* @see #forEach(DoubleConsumer)
*/
void forEachOrdered(DoubleConsumer action);
/**
* Returns an array containing the elements of this stream.
*
* <p>This is a <a href="package-summary.html#StreamOps">terminal
* operation</a>.
*
* @return an array containing the elements of this stream
*/
double[] toArray();
/**
* Performs a <a href="package-summary.html#Reduction">reduction</a> on the
* elements of this stream, using the provided identity value and an
* <a href="package-summary.html#Associativity">associative</a>
* accumulation function, and returns the reduced value. This is equivalent
* to:
* <pre>{@code
* double result = identity;
* for (double element : this stream)
* result = accumulator.apply(result, element)
* return result;
* }</pre>
*
* but is not constrained to execute sequentially.
*
* <p>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
* <a href="package-summary.html#Associativity">associative</a> function.
*
* <p>This is a <a href="package-summary.html#StreamOps">terminal
* operation</a>.
*
* @apiNote Sum, min, max, and average are all special cases of reduction.
* Summing a stream of numbers can be expressed as:
* <pre>{@code
* double sum = numbers.reduce(0, (a, b) -> a+b);
* }</pre>
*
* or more compactly:
*
* <pre>{@code
* double sum = numbers.reduce(0, Double::sum);
* }</pre>
*
* <p>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 <a href="package-summary.html#Associativity">associative</a>
* <a href="package-summary.html#NonInterference">non-interfering,
* stateless</a> 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 <a href="package-summary.html#Reduction">reduction</a> on the
* elements of this stream, using an
* <a href="package-summary.html#Associativity">associative</a> accumulation
* function, and returns an {@code OptionalDouble} describing the reduced
* value, if any. This is equivalent to:
* <pre>{@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();
* }</pre>
*
* but is not constrained to execute sequentially.
*
* <p>The {@code accumulator} function must be an
* <a href="package-summary.html#Associativity">associative</a> function.
*
* <p>This is a <a href="package-summary.html#StreamOps">terminal
* operation</a>.
*
* @param op an <a href="package-summary.html#Associativity">associative</a>
* <a href="package-summary.html#NonInterference">non-interfering,
* stateless</a> function for combining two values
* @return the result of the reduction
* @see #reduce(double, DoubleBinaryOperator)
*/
OptionalDouble reduce(DoubleBinaryOperator op);
/**
* Performs a <a href="package-summary.html#MutableReduction">mutable
* reduction</a> 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 {@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:
* <pre>{@code
* R result = supplier.get();
* for (double element : this stream)
* accumulator.accept(result, element);
* return result;
* }</pre>
*
* <p>Like {@link #reduce(double, DoubleBinaryOperator)}, {@code collect}
* operations can be parallelized without requiring additional
* synchronization.
*
* <p>This is a <a href="package-summary.html#StreamOps">terminal
* operation</a>.
*
* @param <R> type of the result
* @param 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.
* @param accumulator an <a href="package-summary.html#Associativity">associative</a>
* <a href="package-summary.html#NonInterference">non-interfering,
* stateless</a> function for incorporating an additional
* element into a result
* @param combiner an <a href="package-summary.html#Associativity">associative</a>
* <a href="package-summary.html#NonInterference">non-interfering,
* stateless</a> function for combining two values, which
* must be compatible with the accumulator function
* @return the result of the reduction
* @see Stream#collect(Supplier, BiConsumer, BiConsumer)
*/
<R> R collect(Supplier<R> supplier,
ObjDoubleConsumer<R> accumulator,
BiConsumer<R, R> combiner);
/**
* Returns the sum of elements in this stream. The sum returned can vary
* depending upon the order in which elements are encountered. This is due
* to accumulated rounding error in addition of values of differing
* magnitudes. Elements sorted by increasing absolute magnitude tend to
* yield more accurate results. If any stream element is a {@code NaN} or
* the sum is at any point a {@code NaN} then the sum will be {@code NaN}.
* This is a special case of a
* <a href="package-summary.html#Reduction">reduction</a> and is
* equivalent to:
* <pre>{@code
* return reduce(0, Double::sum);
* }</pre>
*
* <p>This is a <a href="package-summary.html#StreamOps">terminal
* operation</a>.
*
* @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
* <a href="package-summary.html#Reduction">reduction</a> and is
* equivalent to:
* <pre>{@code
* return reduce(Double::min);
* }</pre>
*
* <p>This is a <a href="package-summary.html#StreamOps">terminal
* operation</a>.
*
* @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
* <a href="package-summary.html#Reduction">reduction</a> and is
* equivalent to:
* <pre>{@code
* return reduce(Double::max);
* }</pre>
*
* <p>This is a <a href="package-summary.html#StreamOps">terminal
* operation</a>.
*
* @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 <a href="package-summary.html#Reduction">reduction</a> and is
* equivalent to:
* <pre>{@code
* return mapToLong(e -> 1L).sum();
* }</pre>
*
* <p>This is a <a href="package-summary.html#StreamOps">terminal operation</a>.
*
* @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
* <a href="package-summary.html#Reduction">reduction</a>.
*
* <p>This is a <a href="package-summary.html#StreamOps">terminal
* operation</a>.
*
* @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 <a href="package-summary.html#Reduction">reduction</a>.
*
* <p>This is a <a href="package-summary.html#StreamOps">terminal
* operation</a>.
*
* @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.
*
* <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
* terminal operation</a>.
*
* @param predicate a <a href="package-summary.html#NonInterference">non-interfering,
* stateless</a> 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.
*
* <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
* terminal operation</a>.
*
* @param predicate a <a href="package-summary.html#NonInterference">non-interfering,
* stateless</a> 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.
*
* <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
* terminal operation</a>.
*
* @param predicate a <a href="package-summary.html#NonInterference">non-interfering,
* stateless</a> 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, or an empty {@code OptionalDouble} if the stream is empty. If
* the stream has no encounter order, then any element may be returned.
*
* <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
* terminal operation</a>.
*
* @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.
*
* <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
* terminal operation</a>.
*
* <p>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 {@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}.
*
* <p>This is an <a href="package-summary.html#StreamOps">intermediate
* operation</a>.
*
* @return a {@code Stream} consistent of the elements of this stream,
* each boxed to a {@code Double}
*/
Stream<Double> boxed();
@Override
DoubleStream sequential();
@Override
DoubleStream parallel();
@Override
PrimitiveIterator.OfDouble iterator();
@Override
Spliterator.OfDouble spliterator();
// Static factories
/**
* Returns a builder for a {@code DoubleStream}.
*
* @return a stream builder
*/
public static Builder builder() {
return new Streams.DoubleStreamBuilderImpl();
}
/**
* Returns an empty sequential {@code DoubleStream}.
*
* @return an empty sequential stream
*/
public static DoubleStream empty() {
return StreamSupport.doubleStream(Spliterators.emptyDoubleSpliterator(), false);
}
/**
* Returns a sequential {@code DoubleStream} containing a single element.
*
* @param t the single element
* @return a singleton sequential stream
*/
public static DoubleStream of(double t) {
return StreamSupport.doubleStream(new Streams.DoubleStreamBuilderImpl(t), false);
}
/**
* Returns a sequential ordered stream whose elements are the specified values.
*
* @param values the elements of the new stream
* @return the new stream
*/
public static DoubleStream of(double... values) {
return Arrays.stream(values);
}
/**
* Returns an infinite sequential ordered {@code DoubleStream} produced by iterative
* application of a function {@code f} to an initial element {@code seed},
* producing a {@code Stream} consisting of {@code seed}, {@code f(seed)},
* {@code f(f(seed))}, etc.
*
* <p>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 stream where each element is generated by
* the provided {@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 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.
*
* @param a the first stream
* @param b the second stream
* @return the concatenation of the two input 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}.
*
* <p>A stream builder has a lifecycle, which 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:
* <pre>{@code
* accept(t)
* return this;
* }</pre>
*
* @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();
}
}