8012987: Optimizations for Stream.limit/substream
Reviewed-by: mduigou
Contributed-by: Brian Goetz <brian.goetz@oracle.com>, Paul Sandoz <paul.sandoz@oracle.com>
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*
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* accompanied this code).
*
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*
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package java.util.stream;
import java.util.Arrays;
import java.util.IntSummaryStatistics;
import java.util.Objects;
import java.util.OptionalDouble;
import java.util.OptionalInt;
import java.util.PrimitiveIterator;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.BiConsumer;
import java.util.function.Function;
import java.util.function.IntBinaryOperator;
import java.util.function.IntConsumer;
import java.util.function.IntFunction;
import java.util.function.IntPredicate;
import java.util.function.IntSupplier;
import java.util.function.IntToDoubleFunction;
import java.util.function.IntToLongFunction;
import java.util.function.IntUnaryOperator;
import java.util.function.ObjIntConsumer;
import java.util.function.Supplier;
/**
* A sequence of primitive integer elements supporting sequential and parallel
* bulk operations. Streams support lazy intermediate operations (transforming
* a stream to another stream) such as {@code filter} and {@code map}, and terminal
* operations (consuming the contents of a stream to produce a result or
* side-effect), such as {@code forEach}, {@code findFirst}, and {@code
* iterator}. Once an operation has been performed on a stream, it
* is considered <em>consumed</em> and no longer usable for other operations.
*
* <p>For sequential stream pipelines, all operations are performed in the
* <a href="package-summary.html#Ordering">encounter order</a> of the pipeline
* source, if the pipeline source has a defined encounter order.
*
* <p>For parallel stream pipelines, unless otherwise specified, intermediate
* stream operations preserve the <a href="package-summary.html#Ordering">
* encounter order</a> 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 <a href="package-summary.html#NonInterference">non-interference
* requirements</a>, 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(IntConsumer)}), are explicitly nondeterministic for parallel
* execution of stream pipelines.
*
* <p>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 <a href="package-summary.html">java.util.stream</a>
*/
public interface IntStream extends BaseStream<Integer, IntStream> {
/**
* 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
*/
IntStream filter(IntPredicate 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
*/
IntStream map(IntUnaryOperator 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(IntFunction<? extends U> 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(IntToLongFunction 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, stateless</a> function to apply to each
* element
* @return the new stream
*/
DoubleStream mapToDouble(IntToDoubleFunction 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.
*
* <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
* 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:
* <pre>{@code
* orderStream.flatMap(order -> order.getLineItems().stream())...
* }</pre>
*
* @param mapper a <a href="package-summary.html#NonInterference">
* non-interfering, stateless</a> function to apply to
* each element which produces an {@code IntStream} of new
* values
* @return the new stream
* @see Stream#flatMap(Function)
*/
IntStream flatMap(IntFunction<? extends IntStream> mapper);
/**
* Returns a stream consisting of the distinct elements of this stream.
*
* <p>This is a <a href="package-summary.html#StreamOps">stateful
* intermediate operation</a>.
*
* @return the new stream
*/
IntStream distinct();
/**
* Returns a stream consisting of the elements of this stream in sorted
* order.
*
* <p>This is a <a href="package-summary.html#StreamOps">stateful
* intermediate operation</a>.
*
* @return the new stream
*/
IntStream 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.toIntSummaryStastistics());
* }</pre>
*
* @param consumer 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
*/
IntStream peek(IntConsumer consumer);
/**
* 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
*/
IntStream 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.
*
* <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
*/
IntStream 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.
*
* <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}
*/
IntStream 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(IntConsumer 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(IntConsumer)
*/
void forEachOrdered(IntConsumer 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
*/
int[] 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
* int result = identity;
* for (int 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
* int sum = integers.reduce(0, (a, b) -> a+b);
* }</pre>
*
* or more compactly:
*
* <pre>{@code
* int 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 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()
*/
int reduce(int identity, IntBinaryOperator 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 OptionalInt} describing the reduced value,
* if any. This is equivalent to:
* <pre>{@code
* boolean foundAny = false;
* int result = null;
* for (int element : this stream) {
* if (!foundAny) {
* foundAny = true;
* result = element;
* }
* else
* result = accumulator.apply(result, element);
* }
* return foundAny ? OptionalInt.of(result) : OptionalInt.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(int, IntBinaryOperator)
*/
OptionalInt reduce(IntBinaryOperator 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 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:
* <pre>{@code
* R result = resultFactory.get();
* for (int element : this stream)
* accumulator.accept(result, element);
* return result;
* }</pre>
*
* <p>Like {@link #reduce(int, IntBinaryOperator)}, {@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 resultFactory 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> resultFactory,
ObjIntConsumer<R> accumulator,
BiConsumer<R, R> combiner);
/**
* Returns the sum of elements in this stream. This is a special case
* of a <a href="package-summary.html#MutableReduction">reduction</a>
* and is equivalent to:
* <pre>{@code
* return reduce(0, Integer::sum);
* }</pre>
*
* @return the sum of elements in this stream
*/
int sum();
/**
* Returns an {@code OptionalInt} describing the minimum element of this
* stream, or an empty optional if this stream is empty. This is a special
* case of a <a href="package-summary.html#MutableReduction">reduction</a>
* and is equivalent to:
* <pre>{@code
* return reduce(Integer::min);
* }</pre>
*
* <p>This is a <a href="package-summary.html#StreamOps">terminal operation</a>.
*
* @return an {@code OptionalInt} containing the minimum element of this
* stream, or an empty {@code OptionalInt} if the stream is empty
*/
OptionalInt min();
/**
* Returns an {@code OptionalInt} describing the maximum element of this
* stream, or an empty optional if this stream is empty. This is a special
* case of a <a href="package-summary.html#MutableReduction">reduction</a>
* and is equivalent to:
* <pre>{@code
* return reduce(Integer::max);
* }</pre>
*
* <p>This is a <a href="package-summary.html#StreamOps">terminal
* operation</a>.
*
* @return an {@code OptionalInt} containing the maximum element of this
* stream, or an empty {@code OptionalInt} if the stream is empty
*/
OptionalInt max();
/**
* Returns the count of elements in this stream. This is a special case of
* a <a href="package-summary.html#MutableReduction">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 average of elements of
* this stream, or an empty optional if this stream is empty. This is a
* special case of a
* <a href="package-summary.html#MutableReduction">reduction</a>.
*
* @return an {@code OptionalDouble} containing the average element of this
* stream, or an empty optional if the stream is empty
*/
OptionalDouble average();
/**
* Returns an {@code IntSummaryStatistics} describing various
* summary data about the elements of this stream. This is a special
* case of a <a href="package-summary.html#MutableReduction">reduction</a>.
*
* @return an {@code IntSummaryStatistics} describing various summary data
* about the elements of this stream
*/
IntSummaryStatistics 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(IntPredicate 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(IntPredicate 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(IntPredicate predicate);
/**
* Returns an {@link OptionalInt} describing the first element of this
* stream (in the encounter order), or an empty {@code OptionalInt} 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 OptionalInt} describing the first element of this stream,
* or an empty {@code OptionalInt} if the stream is empty
*/
OptionalInt findFirst();
/**
* Returns an {@link OptionalInt} describing some element of the stream, or
* an empty {@code OptionalInt} 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 the first element
* in the encounter order is desired, use {@link #findFirst()} instead.)
*
* @return an {@code OptionalInt} describing some element of this stream, or
* an empty {@code OptionalInt} if the stream is empty
* @see #findFirst()
*/
OptionalInt findAny();
/**
* Returns a {@code LongStream} consisting of the elements of this stream,
* converted to {@code long}.
*
* @return a {@code LongStream} consisting of the elements of this stream,
* converted to {@code long}
*/
LongStream asLongStream();
/**
* Returns a {@code DoubleStream} consisting of the elements of this stream,
* converted to {@code double}.
*
* @return a {@code DoubleStream} consisting of the elements of this stream,
* converted to {@code double}
*/
DoubleStream asDoubleStream();
/**
* Returns a {@code Stream} consisting of the elements of this stream,
* each boxed to an {@code Integer}.
*
* @return a {@code Stream} consistent of the elements of this stream,
* each boxed to an {@code Integer}
*/
Stream<Integer> boxed();
@Override
IntStream sequential();
@Override
IntStream parallel();
@Override
PrimitiveIterator.OfInt iterator();
@Override
Spliterator.OfInt spliterator();
// Static factories
/**
* Returns a builder for an {@code IntStream}.
*
* @return a stream builder
*/
public static StreamBuilder.OfInt builder() {
return new Streams.IntStreamBuilderImpl();
}
/**
* Returns an empty sequential {@code IntStream}.
*
* @return an empty sequential stream
*/
public static IntStream empty() {
return StreamSupport.intStream(Spliterators.emptyIntSpliterator());
}
/**
* Returns a sequential {@code IntStream} containing a single element.
*
* @param t the single element
* @return a singleton sequential stream
*/
public static IntStream of(int t) {
return StreamSupport.intStream(new Streams.IntStreamBuilderImpl(t));
}
/**
* Returns a sequential stream whose elements are the specified values.
*
* @param values the elements of the new stream
* @return the new stream
*/
public static IntStream of(int... values) {
return Arrays.stream(values);
}
/**
* Returns an infinite sequential {@code IntStream} 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 IntStream} 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 IntStream}
*/
public static IntStream iterate(final int seed, final IntUnaryOperator f) {
Objects.requireNonNull(f);
final PrimitiveIterator.OfInt iterator = new PrimitiveIterator.OfInt() {
int t = seed;
@Override
public boolean hasNext() {
return true;
}
@Override
public int nextInt() {
int v = t;
t = f.applyAsInt(t);
return v;
}
};
return StreamSupport.intStream(Spliterators.spliteratorUnknownSize(
iterator,
Spliterator.ORDERED | Spliterator.IMMUTABLE | Spliterator.NONNULL));
}
/**
* Returns a sequential {@code IntStream} where each element is
* generated by an {@code IntSupplier}. This is suitable for generating
* constant streams, streams of random elements, etc.
*
* @param s the {@code IntSupplier} for generated elements
* @return a new sequential {@code IntStream}
*/
public static IntStream generate(IntSupplier s) {
Objects.requireNonNull(s);
return StreamSupport.intStream(
new StreamSpliterators.InfiniteSupplyingSpliterator.OfInt(Long.MAX_VALUE, s));
}
/**
* Returns a sequential {@code IntStream} from {@code startInclusive}
* (inclusive) to {@code endExclusive} (exclusive) by an incremental step of
* {@code 1}.
*
* @apiNote
* <p>An equivalent sequence of increasing values can be produced
* sequentially using a {@code for} loop as follows:
* <pre>{@code
* for (int i = startInclusive; i < endExclusive ; i++) { ... }
* }</pre>
*
* @param startInclusive the (inclusive) initial value
* @param endExclusive the exclusive upper bound
* @return a sequential {@code IntStream} for the range of {@code int}
* elements
*/
public static IntStream range(int startInclusive, int endExclusive) {
if (startInclusive >= endExclusive) {
return empty();
} else {
return StreamSupport.intStream(
new Streams.RangeIntSpliterator(startInclusive, endExclusive, false));
}
}
/**
* Returns a sequential {@code IntStream} from {@code startInclusive}
* (inclusive) to {@code endInclusive} (inclusive) by an incremental step of
* {@code 1}.
*
* @apiNote
* <p>An equivalent sequence of increasing values can be produced
* sequentially using a {@code for} loop as follows:
* <pre>{@code
* for (int i = startInclusive; i <= endInclusive ; i++) { ... }
* }</pre>
*
* @param startInclusive the (inclusive) initial value
* @param endInclusive the inclusive upper bound
* @return a sequential {@code IntStream} for the range of {@code int}
* elements
*/
public static IntStream rangeClosed(int startInclusive, int endInclusive) {
if (startInclusive > endInclusive) {
return empty();
} else {
return StreamSupport.intStream(
new Streams.RangeIntSpliterator(startInclusive, endInclusive, true));
}
}
}