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 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.util.stream;

import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
import java.util.Objects;
import java.util.Optional;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.BiConsumer;
import java.util.function.BiFunction;
import java.util.function.BinaryOperator;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.IntFunction;
import java.util.function.Predicate;
import java.util.function.Supplier;
import java.util.function.ToDoubleFunction;
import java.util.function.ToIntFunction;
import java.util.function.ToLongFunction;
import java.util.function.UnaryOperator;

/**
 * A sequence of elements supporting sequential and parallel aggregate
 * operations. The following example illustrates an aggregate operation using
 * {@link Stream} and {@link IntStream}:
 *
 * <pre>{@code
 * int sum = widgets.stream()
 * .filter(w -> w.getColor() == RED)
 * .mapToInt(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 int} values representing the weight of
 * each red widget. Then this stream is summed to produce a total weight.
 *
 * <p>In addition to {@code Stream}, which is a stream of object references,
 * there are primitive specializations for {@link IntStream}, {@link LongStream},
 * and {@link DoubleStream}, all of which are referred to as "streams" and
 * conform to the characteristics and restrictions described here.
 *
 * <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 I/O channel,
 * etc), zero or more <em>intermediate operations</em> (which transform a
 * stream into another stream, such as {@link Stream#filter(Predicate)}), and a
 * <em>terminal operation</em> (which produces a result or side-effect, such
 * as {@link Stream#count()} or {@link Stream#forEach(Consumer)}).
 * 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>A stream implementation is permitted significant latitude in optimizing
 * the computation of the result. For example, a stream implementation is free
 * to elide operations (or entire stages) from a stream pipeline -- and
 * therefore elide invocation of behavioral parameters -- if it can prove that
 * it would not affect the result of the computation. This means that
 * side-effects of behavioral parameters may not always be executed and should
 * not be relied upon, unless otherwise specified (such as by the terminal
 * operations {@code forEach} and {@code forEachOrdered}). (For a specific
 * example of such an optimization, see the API note documented on the
 * {@link #count} operation. For more detail, see the
 * <a href="package-summary.html#SideEffects">side-effects</a> section of the
 * stream package documentation.)
 *
 * <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 mapToInt} in the example above. To preserve correct behavior,
 * these <em>behavioral parameters</em>:
 * <ul>
 * <li>must be <a href="package-summary.html#NonInterference">non-interfering</a>
 * (they do not modify the stream source); and</li>
 * <li>in most cases must be <a href="package-summary.html#Statelessness">stateless</a>
 * (their result should not depend on any state that might change during execution
 * of the stream pipeline).</li>
 * </ul>
 *
 * <p>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. Unless otherwise specified these parameters must be
 * <em>non-null</em>.
 *
 * <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}.
 * Operating on a stream after it has been closed will throw {@link IllegalStateException}.
 * Most stream instances do not actually need to be closed after use, as they
 * are backed by collections, arrays, or generating functions, which require no
 * special resource management. Generally, only streams whose source is an IO channel,
 * such as those returned by {@link Files#lines(Path)}, will require closing. If a
 * stream does require closing, it must be opened as a resource within a try-with-resources
 * statement or similar control structure to ensure that it is closed promptly after its
 * operations have completed.
 *
 * <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.
 *
 * @param <T> the type of the stream elements
 * @since 1.8
 * @see IntStream
 * @see LongStream
 * @see DoubleStream
 * @see <a href="package-summary.html">java.util.stream</a>
 */
public interface Stream<T> extends BaseStream<T, Stream<T>> {

 /**
 * 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</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * predicate to apply to each element to determine if it
 * should be included
 * @return the new stream
 */
 Stream<T> filter(Predicate<? super T> 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 <R> The element type of the new stream
 * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * function to apply to each element
 * @return the new stream
 */
 <R> Stream<R> map(Function<? super T, ? extends R> 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</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * function to apply to each element
 * @return the new stream
 */
 IntStream mapToInt(ToIntFunction<? super T> 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</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * function to apply to each element
 * @return the new stream
 */
 LongStream mapToLong(ToLongFunction<? super T> mapper);

 /**
 * Returns a {@code DoubleStream} 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</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * function to apply to each element
 * @return the new stream
 */
 DoubleStream mapToDouble(ToDoubleFunction<? super T> 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
 * {@link java.util.stream.BaseStream#close() closed} after its contents
 * have been placed into this stream. (If a mapped stream is {@code null}
 * an empty stream is used, instead.)
 *
 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
 * operation</a>.
 *
 * @apiNote
 * The {@code flatMap()} operation has the effect of applying a one-to-many
 * transformation to the elements of the stream, and then flattening the
 * resulting elements into a new stream.
 *
 * <p><b>Examples.</b>
 *
 * <p>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 containing all the line items in all the orders:
 * <pre>{@code
 * orders.flatMap(order -> order.getLineItems().stream())...
 * }</pre>
 *
 * <p>If {@code path} is the path to a file, then the following produces a
 * stream of the {@code words} contained in that file:
 * <pre>{@code
 * Stream<String> lines = Files.lines(path, StandardCharsets.UTF_8);
 * Stream<String> words = lines.flatMap(line -> Stream.of(line.split(" +")));
 * }</pre>
 * The {@code mapper} function passed to {@code flatMap} splits a line,
 * using a simple regular expression, into an array of words, and then
 * creates a stream of words from that array.
 *
 * @param <R> The element type of the new stream
 * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * function to apply to each element which produces a stream
 * of new values
 * @return the new stream
 */
 <R> Stream<R> flatMap(Function<? super T, ? extends Stream<? extends R>> mapper);

 /**
 * Returns an {@code IntStream} 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 {@link java.util.stream.BaseStream#close() closed} after its
 * contents have been placed into this stream. (If a mapped stream is
 * {@code null} an empty stream is used, instead.)
 *
 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
 * operation</a>.
 *
 * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * function to apply to each element which produces a stream
 * of new values
 * @return the new stream
 * @see #flatMap(Function)
 */
 IntStream flatMapToInt(Function<? super T, ? extends IntStream> mapper);

 /**
 * Returns an {@code LongStream} 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 {@link java.util.stream.BaseStream#close() closed} after its
 * contents have been placed into this stream. (If a mapped stream is
 * {@code null} an empty stream is used, instead.)
 *
 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
 * operation</a>.
 *
 * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * function to apply to each element which produces a stream
 * of new values
 * @return the new stream
 * @see #flatMap(Function)
 */
 LongStream flatMapToLong(Function<? super T, ? extends LongStream> mapper);

 /**
 * Returns an {@code DoubleStream} 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 {@link java.util.stream.BaseStream#close() closed} after its
 * contents have placed been into this stream. (If a mapped stream is
 * {@code null} an empty stream is used, instead.)
 *
 * <p>This is an <a href="package-summary.html#StreamOps">intermediate
 * operation</a>.
 *
 * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * function to apply to each element which produces a stream
 * of new values
 * @return the new stream
 * @see #flatMap(Function)
 */
 DoubleStream flatMapToDouble(Function<? super T, ? extends DoubleStream> mapper);

 /**
 * Returns a stream consisting of the distinct elements (according to
 * {@link Object#equals(Object)}) of this stream.
 *
 * <p>For ordered streams, the selection of distinct elements is stable
 * (for duplicated elements, the element appearing first in the encounter
 * order is preserved.) For unordered streams, no stability guarantees
 * are made.
 *
 * <p>This is a <a href="package-summary.html#StreamOps">stateful
 * intermediate operation</a>.
 *
 * @apiNote
 * Preserving stability for {@code distinct()} in parallel pipelines is
 * relatively expensive (requires that the operation act as a full barrier,
 * with substantial buffering overhead), and stability is often not needed.
 * Using an unordered stream source (such as {@link #generate(Supplier)})
 * or removing the ordering constraint with {@link #unordered()} may result
 * in significantly more efficient execution for {@code distinct()} in parallel
 * pipelines, if the semantics of your situation permit. If consistency
 * with encounter order is required, and you are experiencing poor performance
 * or memory utilization with {@code distinct()} in parallel pipelines,
 * switching to sequential execution with {@link #sequential()} may improve
 * performance.
 *
 * @return the new stream
 */
 Stream<T> distinct();

 /**
 * Returns a stream consisting of the elements of this stream, sorted
 * according to natural order. If the elements of this stream are not
 * {@code Comparable}, a {@code java.lang.ClassCastException} may be thrown
 * when the terminal operation is executed.
 *
 * <p>For ordered streams, the sort is stable. For unordered streams, no
 * stability guarantees are made.
 *
 * <p>This is a <a href="package-summary.html#StreamOps">stateful
 * intermediate operation</a>.
 *
 * @return the new stream
 */
 Stream<T> sorted();

 /**
 * Returns a stream consisting of the elements of this stream, sorted
 * according to the provided {@code Comparator}.
 *
 * <p>For ordered streams, the sort is stable. For unordered streams, no
 * stability guarantees are made.
 *
 * <p>This is a <a href="package-summary.html#StreamOps">stateful
 * intermediate operation</a>.
 *
 * @param comparator a <a href="package-summary.html#NonInterference">non-interfering</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * {@code Comparator} to be used to compare stream elements
 * @return the new stream
 */
 Stream<T> sorted(Comparator<? super T> comparator);

 /**
 * 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
 * Stream.of("one", "two", "three", "four")
 * .filter(e -> e.length() > 3)
 * .peek(e -> System.out.println("Filtered value: " + e))
 * .map(String::toUpperCase)
 * .peek(e -> System.out.println("Mapped value: " + e))
 * .collect(Collectors.toList());
 * }</pre>
 *
 * <p>In cases where the stream implementation is able to optimize away the
 * production of some or all the elements (such as with short-circuiting
 * operations like {@code findFirst}, or in the example described in
 * {@link #count}), the action will not be invoked for those elements.
 *
 * @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
 */
 Stream<T> peek(Consumer<? super T> 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>.
 *
 * @apiNote
 * While {@code limit()} is generally a cheap operation on sequential
 * stream pipelines, it can be quite expensive on ordered parallel pipelines,
 * especially for large values of {@code maxSize}, since {@code limit(n)}
 * is constrained to return not just any <em>n</em> elements, but the
 * <em>first n</em> elements in the encounter order. Using an unordered
 * stream source (such as {@link #generate(Supplier)}) or removing the
 * ordering constraint with {@link #unordered()} may result in significant
 * speedups of {@code limit()} in parallel pipelines, if the semantics of
 * your situation permit. If consistency with encounter order is required,
 * and you are experiencing poor performance or memory utilization with
 * {@code limit()} in parallel pipelines, switching to sequential execution
 * with {@link #sequential()} may improve performance.
 *
 * @param maxSize the number of elements the stream should be limited to
 * @return the new stream
 * @throws IllegalArgumentException if {@code maxSize} is negative
 */
 Stream<T> limit(long maxSize);

 /**
 * Returns a stream consisting of the remaining elements of this stream
 * after discarding the first {@code n} elements of the stream.
 * If this stream contains fewer than {@code n} elements then an
 * empty stream will be returned.
 *
 * <p>This is a <a href="package-summary.html#StreamOps">stateful
 * intermediate operation</a>.
 *
 * @apiNote
 * While {@code skip()} is generally a cheap operation on sequential
 * stream pipelines, it can be quite expensive on ordered parallel pipelines,
 * especially for large values of {@code n}, since {@code skip(n)}
 * is constrained to skip not just any <em>n</em> elements, but the
 * <em>first n</em> elements in the encounter order. Using an unordered
 * stream source (such as {@link #generate(Supplier)}) or removing the
 * ordering constraint with {@link #unordered()} may result in significant
 * speedups of {@code skip()} in parallel pipelines, if the semantics of
 * your situation permit. If consistency with encounter order is required,
 * and you are experiencing poor performance or memory utilization with
 * {@code skip()} in parallel pipelines, switching to sequential execution
 * with {@link #sequential()} may improve performance.
 *
 * @param n the number of leading elements to skip
 * @return the new stream
 * @throws IllegalArgumentException if {@code n} is negative
 */
 Stream<T> skip(long n);

 /**
 * 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.
 *
 * <p>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.
 *
 * <p>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).
 *
 * <p>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).
 *
 * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
 * stateful intermediate operation</a>.
 *
 * @implSpec
 * The default implementation obtains the {@link #spliterator() spliterator}
 * of this stream, wraps that spliterator so as to support the semantics
 * of this operation on traversal, and returns a new stream associated with
 * the wrapped spliterator. The returned stream preserves the execution
 * characteristics of this stream (namely parallel or sequential execution
 * as per {@link #isParallel()}) but the wrapped spliterator may choose to
 * not support splitting. When the returned stream is closed, the close
 * handlers for both the returned and this stream are invoked.
 *
 * @apiNote
 * While {@code takeWhile()} is generally a cheap operation on sequential
 * stream pipelines, it can be quite expensive on ordered parallel
 * pipelines, since the operation is constrained to return not just any
 * valid prefix, but the longest prefix of elements in the encounter order.
 * Using an unordered stream source (such as {@link #generate(Supplier)}) or
 * removing the ordering constraint with {@link #unordered()} may result in
 * significant speedups of {@code takeWhile()} in parallel pipelines, if the
 * semantics of your situation permit. If consistency with encounter order
 * is required, and you are experiencing poor performance or memory
 * utilization with {@code takeWhile()} in parallel pipelines, switching to
 * sequential execution with {@link #sequential()} may improve performance.
 *
 * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * predicate to apply to elements to determine the longest
 * prefix of elements.
 * @return the new stream
 * @since 9
 */
 default Stream<T> takeWhile(Predicate<? super T> predicate) {
 Objects.requireNonNull(predicate);
 // Reuses the unordered spliterator, which, when encounter is present,
 // is safe to use as long as it configured not to split
 return StreamSupport.stream(
 new WhileOps.UnorderedWhileSpliterator.OfRef.Taking<>(spliterator(), true, predicate),
 isParallel()).onClose(this::close);
 }

 /**
 * 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.
 *
 * <p>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.
 *
 * <p>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).
 *
 * <p>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).
 *
 * <p>This is a <a href="package-summary.html#StreamOps">stateful
 * intermediate operation</a>.
 *
 * @implSpec
 * The default implementation obtains the {@link #spliterator() spliterator}
 * of this stream, wraps that spliterator so as to support the semantics
 * of this operation on traversal, and returns a new stream associated with
 * the wrapped spliterator. The returned stream preserves the execution
 * characteristics of this stream (namely parallel or sequential execution
 * as per {@link #isParallel()}) but the wrapped spliterator may choose to
 * not support splitting. When the returned stream is closed, the close
 * handlers for both the returned and this stream are invoked.
 *
 * @apiNote
 * While {@code dropWhile()} is generally a cheap operation on sequential
 * stream pipelines, it can be quite expensive on ordered parallel
 * pipelines, since the operation is constrained to return not just any
 * valid prefix, but the longest prefix of elements in the encounter order.
 * Using an unordered stream source (such as {@link #generate(Supplier)}) or
 * removing the ordering constraint with {@link #unordered()} may result in
 * significant speedups of {@code dropWhile()} in parallel pipelines, if the
 * semantics of your situation permit. If consistency with encounter order
 * is required, and you are experiencing poor performance or memory
 * utilization with {@code dropWhile()} in parallel pipelines, switching to
 * sequential execution with {@link #sequential()} may improve performance.
 *
 * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * predicate to apply to elements to determine the longest
 * prefix of elements.
 * @return the new stream
 * @since 9
 */
 default Stream<T> dropWhile(Predicate<? super T> predicate) {
 Objects.requireNonNull(predicate);
 // Reuses the unordered spliterator, which, when encounter is present,
 // is safe to use as long as it configured not to split
 return StreamSupport.stream(
 new WhileOps.UnorderedWhileSpliterator.OfRef.Dropping<>(spliterator(), true, predicate),
 isParallel()).onClose(this::close);
 }

 /**
 * Performs an action for each element of this stream.
 *
 * <p>This is a <a href="package-summary.html#StreamOps">terminal
 * operation</a>.
 *
 * <p>The behavior of this operation is explicitly nondeterministic.
 * 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(Consumer<? super T> action);

 /**
 * Performs an action for each element of this stream, in the encounter
 * order of the stream if the stream has a defined encounter order.
 *
 * <p>This is a <a href="package-summary.html#StreamOps">terminal
 * operation</a>.
 *
 * <p>This operation processes the elements one at a time, in encounter
 * order if one exists. Performing the action for one element
 * <a href="../concurrent/package-summary.html#MemoryVisibility"><i>happens-before</i></a>
 * performing the action for subsequent elements, but for any given element,
 * the action may be performed in whatever thread the library chooses.
 *
 * @param action a <a href="package-summary.html#NonInterference">
 * non-interfering</a> action to perform on the elements
 * @see #forEach(Consumer)
 */
 void forEachOrdered(Consumer<? super T> 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, whose {@linkplain Class#getComponentType runtime component
 * type} is {@code Object}, containing the elements of this stream
 */
 Object[] toArray();

 /**
 * Returns an array containing the elements of this stream, using the
 * provided {@code generator} function to allocate the returned array, as
 * well as any additional arrays that might be required for a partitioned
 * execution or for resizing.
 *
 * <p>This is a <a href="package-summary.html#StreamOps">terminal
 * operation</a>.
 *
 * @apiNote
 * The generator function takes an integer, which is the size of the
 * desired array, and produces an array of the desired size. This can be
 * concisely expressed with an array constructor reference:
 * <pre>{@code
 * Person[] men = people.stream()
 * .filter(p -> p.getGender() == MALE)
 * .toArray(Person[]::new);
 * }</pre>
 *
 * @param <A> the component type of the resulting array
 * @param generator a function which produces a new array of the desired
 * type and the provided length
 * @return an array containing the elements in this stream
 * @throws ArrayStoreException if the runtime type of any element of this
 * stream is not assignable to the {@linkplain Class#getComponentType
 * runtime component type} of the generated array
 */
 <A> A[] toArray(IntFunction<A[]> generator);

 /**
 * 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
 * T result = identity;
 * for (T 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 t},
 * {@code accumulator.apply(identity, t)} is equal to {@code t}.
 * 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, average, and string concatenation are all special
 * cases of reduction. Summing a stream of numbers can be expressed as:
 *
 * <pre>{@code
 * Integer sum = integers.reduce(0, (a, b) -> a+b);
 * }</pre>
 *
 * or:
 *
 * <pre>{@code
 * Integer sum = integers.reduce(0, Integer::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 accumulator an <a href="package-summary.html#Associativity">associative</a>,
 * <a href="package-summary.html#NonInterference">non-interfering</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * function for combining two values
 * @return the result of the reduction
 */
 T reduce(T identity, BinaryOperator<T> accumulator);

 /**
 * 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 Optional} describing the reduced value,
 * if any. This is equivalent to:
 * <pre>{@code
 * boolean foundAny = false;
 * T result = null;
 * for (T element : this stream) {
 * if (!foundAny) {
 * foundAny = true;
 * result = element;
 * }
 * else
 * result = accumulator.apply(result, element);
 * }
 * return foundAny ? Optional.of(result) : Optional.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 accumulator an <a href="package-summary.html#Associativity">associative</a>,
 * <a href="package-summary.html#NonInterference">non-interfering</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * function for combining two values
 * @return an {@link Optional} describing the result of the reduction
 * @throws NullPointerException if the result of the reduction is null
 * @see #reduce(Object, BinaryOperator)
 * @see #min(Comparator)
 * @see #max(Comparator)
 */
 Optional<T> reduce(BinaryOperator<T> accumulator);

 /**
 * Performs a <a href="package-summary.html#Reduction">reduction</a> on the
 * elements of this stream, using the provided identity, accumulation and
 * combining functions. This is equivalent to:
 * <pre>{@code
 * U result = identity;
 * for (T 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 combiner
 * function. This means that for all {@code u}, {@code combiner(identity, u)}
 * is equal to {@code u}. Additionally, the {@code combiner} function
 * must be compatible with the {@code accumulator} function; for all
 * {@code u} and {@code t}, the following must hold:
 * <pre>{@code
 * combiner.apply(u, accumulator.apply(identity, t)) == accumulator.apply(u, t)
 * }</pre>
 *
 * <p>This is a <a href="package-summary.html#StreamOps">terminal
 * operation</a>.
 *
 * @apiNote Many reductions using this form can be represented more simply
 * by an explicit combination of {@code map} and {@code reduce} operations.
 * The {@code accumulator} function acts as a fused mapper and accumulator,
 * which can sometimes be more efficient than separate mapping and reduction,
 * such as when knowing the previously reduced value allows you to avoid
 * some computation.
 *
 * @param <U> The type of the result
 * @param identity the identity value for the combiner function
 * @param accumulator an <a href="package-summary.html#Associativity">associative</a>,
 * <a href="package-summary.html#NonInterference">non-interfering</a>,
 * <a href="package-summary.html#Statelessness">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</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * function for combining two values, which must be
 * compatible with the accumulator function
 * @return the result of the reduction
 * @see #reduce(BinaryOperator)
 * @see #reduce(Object, BinaryOperator)
 */
 <U> U reduce(U identity,
 BiFunction<U, ? super T, U> accumulator,
 BinaryOperator<U> combiner);

 /**
 * 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 (T element : this stream)
 * accumulator.accept(result, element);
 * return result;
 * }</pre>
 *
 * <p>Like {@link #reduce(Object, BinaryOperator)}, {@code collect} operations
 * can be parallelized without requiring additional synchronization.
 *
 * <p>This is a <a href="package-summary.html#StreamOps">terminal
 * operation</a>.
 *
 * @apiNote There are many existing classes in the JDK whose signatures are
 * well-suited for use with method references as arguments to {@code collect()}.
 * For example, the following will accumulate strings into an {@code ArrayList}:
 * <pre>{@code
 * List<String> asList = stringStream.collect(ArrayList::new, ArrayList::add,
 * ArrayList::addAll);
 * }</pre>
 *
 * <p>The following will take a stream of strings and concatenates them into a
 * single string:
 * <pre>{@code
 * String concat = stringStream.collect(StringBuilder::new, StringBuilder::append,
 * StringBuilder::append)
 * .toString();
 * }</pre>
 *
 * @param <R> the type of the mutable result container
 * @param supplier a function that creates a new mutable 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</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * function that must fold an element into a result
 * container.
 * @param combiner an <a href="package-summary.html#Associativity">associative</a>,
 * <a href="package-summary.html#NonInterference">non-interfering</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * function that accepts two partial result containers
 * and merges them, which must be compatible with the
 * accumulator function. The combiner function must fold
 * the elements from the second result container into the
 * first result container.
 * @return the result of the reduction
 */
 <R> R collect(Supplier<R> supplier,
 BiConsumer<R, ? super T> accumulator,
 BiConsumer<R, R> combiner);

 /**
 * Performs a <a href="package-summary.html#MutableReduction">mutable
 * reduction</a> operation on the elements of this stream using a
 * {@code Collector}. A {@code Collector}
 * encapsulates the functions used as arguments to
 * {@link #collect(Supplier, BiConsumer, BiConsumer)}, allowing for reuse of
 * collection strategies and composition of collect operations such as
 * multiple-level grouping or partitioning.
 *
 * <p>If the stream is parallel, and the {@code Collector}
 * is {@link Collector.Characteristics#CONCURRENT concurrent}, and
 * either the stream is unordered or the collector is
 * {@link Collector.Characteristics#UNORDERED unordered},
 * then a concurrent reduction will be performed (see {@link Collector} for
 * details on concurrent reduction.)
 *
 * <p>This is a <a href="package-summary.html#StreamOps">terminal
 * operation</a>.
 *
 * <p>When executed in parallel, multiple intermediate results may be
 * instantiated, populated, and merged so as to maintain isolation of
 * mutable data structures. Therefore, even when executed in parallel
 * with non-thread-safe data structures (such as {@code ArrayList}), no
 * additional synchronization is needed for a parallel reduction.
 *
 * @apiNote
 * The following will accumulate strings into an ArrayList:
 * <pre>{@code
 * List<String> asList = stringStream.collect(Collectors.toList());
 * }</pre>
 *
 * <p>The following will classify {@code Person} objects by city:
 * <pre>{@code
 * Map<String, List<Person>> peopleByCity
 * = personStream.collect(Collectors.groupingBy(Person::getCity));
 * }</pre>
 *
 * <p>The following will classify {@code Person} objects by state and city,
 * cascading two {@code Collector}s together:
 * <pre>{@code
 * Map<String, Map<String, List<Person>>> peopleByStateAndCity
 * = personStream.collect(Collectors.groupingBy(Person::getState,
 * Collectors.groupingBy(Person::getCity)));
 * }</pre>
 *
 * @param <R> the type of the result
 * @param <A> the intermediate accumulation type of the {@code Collector}
 * @param collector the {@code Collector} describing the reduction
 * @return the result of the reduction
 * @see #collect(Supplier, BiConsumer, BiConsumer)
 * @see Collectors
 */
 <R, A> R collect(Collector<? super T, A, R> collector);

 /**
 * Returns the minimum element of this stream according to the provided
 * {@code Comparator}. 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>.
 *
 * @param comparator a <a href="package-summary.html#NonInterference">non-interfering</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * {@code Comparator} to compare elements of this stream
 * @return an {@code Optional} describing the minimum element of this stream,
 * or an empty {@code Optional} if the stream is empty
 * @throws NullPointerException if the minimum element is null
 */
 Optional<T> min(Comparator<? super T> comparator);

 /**
 * Returns the maximum element of this stream according to the provided
 * {@code Comparator}. 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>.
 *
 * @param comparator a <a href="package-summary.html#NonInterference">non-interfering</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * {@code Comparator} to compare elements of this stream
 * @return an {@code Optional} describing the maximum element of this stream,
 * or an empty {@code Optional} if the stream is empty
 * @throws NullPointerException if the maximum element is null
 */
 Optional<T> max(Comparator<? super T> comparator);

 /**
 * 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>.
 *
 * @apiNote
 * An implementation may choose to not execute the stream pipeline (either
 * sequentially or in parallel) if it is capable of computing the count
 * directly from the stream source. In such cases no source elements will
 * be traversed and no intermediate operations will be evaluated.
 * Behavioral parameters with side-effects, which are strongly discouraged
 * except for harmless cases such as debugging, may be affected. For
 * example, consider the following stream:
 * <pre>{@code
 * List<String> l = Arrays.asList("A", "B", "C", "D");
 * long count = l.stream().peek(System.out::println).count();
 * }</pre>
 * The number of elements covered by the stream source, a {@code List}, is
 * known and the intermediate operation, {@code peek}, does not inject into
 * or remove elements from the stream (as may be the case for
 * {@code flatMap} or {@code filter} operations). Thus the count is the
 * size of the {@code List} and there is no need to execute the pipeline
 * and, as a side-effect, print out the list elements.
 *
 * @return the count of elements in this stream
 */
 long count();

 /**
 * 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
 * {@code false} is returned and the predicate is not evaluated.
 *
 * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
 * terminal operation</a>.
 *
 * @apiNote
 * This method evaluates the <em>existential quantification</em> of the
 * predicate over the elements of the stream (for some x P(x)).
 *
 * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>,
 * <a href="package-summary.html#Statelessness">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(Predicate<? super T> 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 {@code true} is
 * returned and the predicate is not evaluated.
 *
 * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
 * terminal operation</a>.
 *
 * @apiNote
 * This method evaluates the <em>universal quantification</em> of the
 * predicate over the elements of the stream (for all x P(x)). If the
 * stream is empty, the quantification is said to be <em>vacuously
 * satisfied</em> and is always {@code true} (regardless of P(x)).
 *
 * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * predicate to apply to elements of this stream
 * @return {@code true} if either all elements of the stream match the
 * provided predicate or the stream is empty, otherwise {@code false}
 */
 boolean allMatch(Predicate<? super T> 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 {@code true} is
 * returned and the predicate is not evaluated.
 *
 * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
 * terminal operation</a>.
 *
 * @apiNote
 * This method evaluates the <em>universal quantification</em> of the
 * negated predicate over the elements of the stream (for all x ~P(x)). If
 * the stream is empty, the quantification is said to be vacuously satisfied
 * and is always {@code true}, regardless of P(x).
 *
 * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>,
 * <a href="package-summary.html#Statelessness">stateless</a>
 * predicate to apply to elements of this stream
 * @return {@code true} if either no elements of the stream match the
 * provided predicate or the stream is empty, otherwise {@code false}
 */
 boolean noneMatch(Predicate<? super T> predicate);

 /**
 * Returns an {@link Optional} describing the first element of this stream,
 * or an empty {@code Optional} 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 Optional} describing the first element of this stream,
 * or an empty {@code Optional} if the stream is empty
 * @throws NullPointerException if the element selected is null
 */
 Optional<T> findFirst();

 /**
 * Returns an {@link Optional} describing some element of the stream, or an
 * empty {@code Optional} 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 Optional} describing some element of this stream, or an
 * empty {@code Optional} if the stream is empty
 * @throws NullPointerException if the element selected is null
 * @see #findFirst()
 */
 Optional<T> findAny();

 // Static factories

 /**
 * Returns a builder for a {@code Stream}.
 *
 * @param <T> type of elements
 * @return a stream builder
 */
 public static<T> Builder<T> builder() {
 return new Streams.StreamBuilderImpl<>();
 }

 /**
 * Returns an empty sequential {@code Stream}.
 *
 * @param <T> the type of stream elements
 * @return an empty sequential stream
 */
 public static<T> Stream<T> empty() {
 return StreamSupport.stream(Spliterators.<T>emptySpliterator(), false);
 }

 /**
 * Returns a sequential {@code Stream} containing a single element.
 *
 * @param t the single element
 * @param <T> the type of stream elements
 * @return a singleton sequential stream
 */
 public static<T> Stream<T> of(T t) {
 return StreamSupport.stream(new Streams.StreamBuilderImpl<>(t), false);
 }

 /**
 * Returns a sequential {@code Stream} containing a single element, if
 * non-null, otherwise returns an empty {@code Stream}.
 *
 * @param t the single element
 * @param <T> the type of stream elements
 * @return a stream with a single element if the specified element
 * is non-null, otherwise an empty stream
 * @since 9
 */
 public static<T> Stream<T> ofNullable(T t) {
 return t == null ? Stream.empty()
 : StreamSupport.stream(new Streams.StreamBuilderImpl<>(t), false);
 }

 /**
 * Returns a sequential ordered stream whose elements are the specified values.
 *
 * @param <T> the type of stream elements
 * @param values the elements of the new stream
 * @return the new stream
 */
 @SafeVarargs
 @SuppressWarnings("varargs") // Creating a stream from an array is safe
 public static<T> Stream<T> of(T... values) {
 return Arrays.stream(values);
 }

 /**
 * Returns an infinite sequential ordered {@code Stream} 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 Stream} 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}.
 *
 * <p>The action of applying {@code f} for one element
 * <a href="../concurrent/package-summary.html#MemoryVisibility"><i>happens-before</i></a>
 * the action of applying {@code f} for subsequent elements. For any given
 * element the action may be performed in whatever thread the library
 * chooses.
 *
 * @param <T> the type of stream elements
 * @param seed the initial element
 * @param f a function to be applied to the previous element to produce
 * a new element
 * @return a new sequential {@code Stream}
 */
 public static<T> Stream<T> iterate(final T seed, final UnaryOperator<T> f) {
 Objects.requireNonNull(f);
 Spliterator<T> spliterator = new Spliterators.AbstractSpliterator<>(Long.MAX_VALUE,
 Spliterator.ORDERED | Spliterator.IMMUTABLE) {
 T prev;
 boolean started;

 @Override
 public boolean tryAdvance(Consumer<? super T> action) {
 Objects.requireNonNull(action);
 T t;
 if (started)
 t = f.apply(prev);
 else {
 t = seed;
 started = true;
 }
 action.accept(prev = t);
 return true;
 }
 };
 return StreamSupport.stream(spliterator, false);
 }

 /**
 * Returns a sequential ordered {@code Stream} produced by iterative
 * application of the given {@code next} function to an initial element,
 * conditioned on satisfying the given {@code hasNext} predicate. The
 * stream terminates as soon as the {@code hasNext} predicate returns false.
 *
 * <p>{@code Stream.iterate} should produce the same sequence of elements as
 * produced by the corresponding for-loop:
 * <pre>{@code
 * for (T index=seed; hasNext.test(index); index = next.apply(index)) {
 * ...
 * }
 * }</pre>
 *
 * <p>The resulting sequence may be empty if the {@code hasNext} predicate
 * does not hold on the seed value. Otherwise the first element will be the
 * supplied {@code seed} value, the next element (if present) will be the
 * result of applying the {@code next} function to the {@code seed} value,
 * and so on iteratively until the {@code hasNext} predicate indicates that
 * the stream should terminate.
 *
 * <p>The action of applying the {@code hasNext} predicate to an element
 * <a href="../concurrent/package-summary.html#MemoryVisibility"><i>happens-before</i></a>
 * the action of applying the {@code next} function to that element. The
 * action of applying the {@code next} function for one element
 * <i>happens-before</i> the action of applying the {@code hasNext}
 * predicate for subsequent elements. For any given element an action may
 * be performed in whatever thread the library chooses.
 *
 * @param <T> the type of stream elements
 * @param seed the initial element
 * @param hasNext a predicate to apply to elements to determine when the
 * stream must terminate.
 * @param next a function to be applied to the previous element to produce
 * a new element
 * @return a new sequential {@code Stream}
 * @since 9
 */
 public static<T> Stream<T> iterate(T seed, Predicate<? super T> hasNext, UnaryOperator<T> next) {
 Objects.requireNonNull(next);
 Objects.requireNonNull(hasNext);
 Spliterator<T> spliterator = new Spliterators.AbstractSpliterator<>(Long.MAX_VALUE,
 Spliterator.ORDERED | Spliterator.IMMUTABLE) {
 T prev;
 boolean started, finished;

 @Override
 public boolean tryAdvance(Consumer<? super T> action) {
 Objects.requireNonNull(action);
 if (finished)
 return false;
 T t;
 if (started)
 t = next.apply(prev);
 else {
 t = seed;
 started = true;
 }
 if (!hasNext.test(t)) {
 prev = null;
 finished = true;
 return false;
 }
 action.accept(prev = t);
 return true;
 }

 @Override
 public void forEachRemaining(Consumer<? super T> action) {
 Objects.requireNonNull(action);
 if (finished)
 return;
 finished = true;
 T t = started ? next.apply(prev) : seed;
 prev = null;
 while (hasNext.test(t)) {
 action.accept(t);
 t = next.apply(t);
 }
 }
 };
 return StreamSupport.stream(spliterator, false);
 }

 /**
 * Returns an infinite sequential unordered stream where each element is
 * generated by the provided {@code Supplier}. This is suitable for
 * generating constant streams, streams of random elements, etc.
 *
 * @param <T> the type of stream elements
 * @param s the {@code Supplier} of generated elements
 * @return a new infinite sequential unordered {@code Stream}
 */
 public static<T> Stream<T> generate(Supplier<? extends T> s) {
 Objects.requireNonNull(s);
 return StreamSupport.stream(
 new StreamSpliterators.InfiniteSupplyingSpliterator.OfRef<>(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.
 *
 * <p>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.
 *
 * @implNote
 * Use caution when constructing streams from repeated concatenation.
 * Accessing an element of a deeply concatenated stream can result in deep
 * call chains, or even {@code StackOverflowError}.
 *
 * <p>Subsequent changes to the sequential/parallel execution mode of the
 * returned stream are not guaranteed to be propagated to the input streams.
 *
 * @apiNote
 * To preserve optimization opportunities this method binds each stream to
 * its source and accepts only two streams as parameters. For example, the
 * exact size of the concatenated stream source can be computed if the exact
 * size of each input stream source is known.
 * To concatenate more streams without binding, or without nested calls to
 * this method, try creating a stream of streams and flat-mapping with the
 * identity function, for example:
 * <pre>{@code
 * Stream<T> concat = Stream.of(s1, s2, s3, s4).flatMap(s -> s);
 * }</pre>
 *
 * @param <T> The type of stream elements
 * @param a the first stream
 * @param b the second stream
 * @return the concatenation of the two input streams
 */
 public static <T> Stream<T> concat(Stream<? extends T> a, Stream<? extends T> b) {
 Objects.requireNonNull(a);
 Objects.requireNonNull(b);

 @SuppressWarnings("unchecked")
 Spliterator<T> split = new Streams.ConcatSpliterator.OfRef<>(
 (Spliterator<T>) a.spliterator(), (Spliterator<T>) b.spliterator());
 Stream<T> stream = StreamSupport.stream(split, a.isParallel() || b.isParallel());
 return stream.onClose(Streams.composedClose(a, b));
 }

 /**
 * A mutable builder for a {@code Stream}. This allows the creation of a
 * {@code Stream} by generating elements individually and adding them to the
 * {@code Builder} (without the copying overhead that comes from using
 * an {@code ArrayList} as a temporary buffer.)
 *
 * <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
 * {@code Stream} whose elements are the elements that were added to the stream
 * builder, in the order they were added.
 *
 * @param <T> the type of stream elements
 * @see Stream#builder()
 * @since 1.8
 */
 public interface Builder<T> extends Consumer<T> {

 /**
 * Adds an element to the stream being built.
 *
 * @throws IllegalStateException if the builder has already transitioned to
 * the built state
 */
 @Override
 void accept(T 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<T> add(T 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
 */
 Stream<T> build();

 }
}