Back to index...

	/*
	* Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/
	package java.util.stream;

	import java.util.Objects;
	import java.util.Optional;
	import java.util.OptionalDouble;
	import java.util.OptionalInt;
	import java.util.OptionalLong;
	import java.util.Spliterator;
	import java.util.concurrent.CountedCompleter;
	import java.util.function.BiConsumer;
	import java.util.function.BiFunction;
	import java.util.function.BinaryOperator;
	import java.util.function.DoubleBinaryOperator;
	import java.util.function.IntBinaryOperator;
	import java.util.function.LongBinaryOperator;
	import java.util.function.ObjDoubleConsumer;
	import java.util.function.ObjIntConsumer;
	import java.util.function.ObjLongConsumer;
	import java.util.function.Supplier;

	/**
	* Factory for creating instances of {@code TerminalOp} that implement
	* reductions.
	*
	* @since 1.8
	*/
	final class ReduceOps {

	private ReduceOps() { }

	/**
	* Constructs a {@code TerminalOp} that implements a functional reduce on
	* reference values.
	*
	* @param <T> the type of the input elements
	* @param <U> the type of the result
	* @param seed the identity element for the reduction
	* @param reducer the accumulating function that incorporates an additional
	* input element into the result
	* @param combiner the combining function that combines two intermediate
	* results
	* @return a {@code TerminalOp} implementing the reduction
	*/
	public static <T, U> TerminalOp<T, U>
	makeRef(U seed, BiFunction<U, ? super T, U> reducer, BinaryOperator<U> combiner) {
	Objects.requireNonNull(reducer);
	Objects.requireNonNull(combiner);
	class ReducingSink extends Box<U> implements AccumulatingSink<T, U, ReducingSink> {
	@Override
	public void begin(long size) {
	state = seed;
	}

	@Override
	public void accept(T t) {
	state = reducer.apply(state, t);
	}

	@Override
	public void combine(ReducingSink other) {
	state = combiner.apply(state, other.state);
	}
	}
	return new ReduceOp<T, U, ReducingSink>(StreamShape.REFERENCE) {
	@Override
	public ReducingSink makeSink() {
	return new ReducingSink();
	}
	};
	}

	/**
	* Constructs a {@code TerminalOp} that implements a functional reduce on
	* reference values producing an optional reference result.
	*
	* @param <T> The type of the input elements, and the type of the result
	* @param operator The reducing function
	* @return A {@code TerminalOp} implementing the reduction
	*/
	public static <T> TerminalOp<T, Optional<T>>
	makeRef(BinaryOperator<T> operator) {
	Objects.requireNonNull(operator);
	class ReducingSink
	implements AccumulatingSink<T, Optional<T>, ReducingSink> {
	private boolean empty;
	private T state;

	public void begin(long size) {
	empty = true;
	state = null;
	}

	@Override
	public void accept(T t) {
	if (empty) {
	empty = false;
	state = t;
	} else {
	state = operator.apply(state, t);
	}
	}

	@Override
	public Optional<T> get() {
	return empty ? Optional.empty() : Optional.of(state);
	}

	@Override
	public void combine(ReducingSink other) {
	if (!other.empty)
	accept(other.state);
	}
	}
	return new ReduceOp<T, Optional<T>, ReducingSink>(StreamShape.REFERENCE) {
	@Override
	public ReducingSink makeSink() {
	return new ReducingSink();
	}
	};
	}

	/**
	* Constructs a {@code TerminalOp} that implements a mutable reduce on
	* reference values.
	*
	* @param <T> the type of the input elements
	* @param <I> the type of the intermediate reduction result
	* @param collector a {@code Collector} defining the reduction
	* @return a {@code ReduceOp} implementing the reduction
	*/
	public static <T, I> TerminalOp<T, I>
	makeRef(Collector<? super T, I, ?> collector) {
	Supplier<I> supplier = Objects.requireNonNull(collector).supplier();
	BiConsumer<I, ? super T> accumulator = collector.accumulator();
	BinaryOperator<I> combiner = collector.combiner();
	class ReducingSink extends Box<I>
	implements AccumulatingSink<T, I, ReducingSink> {
	@Override
	public void begin(long size) {
	state = supplier.get();
	}

	@Override
	public void accept(T t) {
	accumulator.accept(state, t);
	}

	@Override
	public void combine(ReducingSink other) {
	state = combiner.apply(state, other.state);
	}
	}
	return new ReduceOp<T, I, ReducingSink>(StreamShape.REFERENCE) {
	@Override
	public ReducingSink makeSink() {
	return new ReducingSink();
	}

	@Override
	public int getOpFlags() {
	return collector.characteristics().contains(Collector.Characteristics.UNORDERED)
	? StreamOpFlag.NOT_ORDERED
	: 0;
	}
	};
	}

	/**
	* Constructs a {@code TerminalOp} that implements a mutable reduce on
	* reference values.
	*
	* @param <T> the type of the input elements
	* @param <R> the type of the result
	* @param seedFactory a factory to produce a new base accumulator
	* @param accumulator a function to incorporate an element into an
	* accumulator
	* @param reducer a function to combine an accumulator into another
	* @return a {@code TerminalOp} implementing the reduction
	*/
	public static <T, R> TerminalOp<T, R>
	makeRef(Supplier<R> seedFactory,
	BiConsumer<R, ? super T> accumulator,
	BiConsumer<R,R> reducer) {
	Objects.requireNonNull(seedFactory);
	Objects.requireNonNull(accumulator);
	Objects.requireNonNull(reducer);
	class ReducingSink extends Box<R>
	implements AccumulatingSink<T, R, ReducingSink> {
	@Override
	public void begin(long size) {
	state = seedFactory.get();
	}

	@Override
	public void accept(T t) {
	accumulator.accept(state, t);
	}

	@Override
	public void combine(ReducingSink other) {
	reducer.accept(state, other.state);
	}
	}
	return new ReduceOp<T, R, ReducingSink>(StreamShape.REFERENCE) {
	@Override
	public ReducingSink makeSink() {
	return new ReducingSink();
	}
	};
	}

	/**
	* Constructs a {@code TerminalOp} that counts the number of stream
	* elements. If the size of the pipeline is known then count is the size
	* and there is no need to evaluate the pipeline. If the size of the
	* pipeline is non known then count is produced, via reduction, using a
	* {@link CountingSink}.
	*
	* @param <T> the type of the input elements
	* @return a {@code TerminalOp} implementing the counting
	*/
	public static <T> TerminalOp<T, Long>
	makeRefCounting() {
	return new ReduceOp<T, Long, CountingSink<T>>(StreamShape.REFERENCE) {
	@Override
	public CountingSink<T> makeSink() { return new CountingSink.OfRef<>(); }

	@Override
	public <P_IN> Long evaluateSequential(PipelineHelper<T> helper,
	Spliterator<P_IN> spliterator) {
	if (StreamOpFlag.SIZED.isKnown(helper.getStreamAndOpFlags()))
	return spliterator.getExactSizeIfKnown();
	return super.evaluateSequential(helper, spliterator);
	}

	@Override
	public <P_IN> Long evaluateParallel(PipelineHelper<T> helper,
	Spliterator<P_IN> spliterator) {
	if (StreamOpFlag.SIZED.isKnown(helper.getStreamAndOpFlags()))
	return spliterator.getExactSizeIfKnown();
	return super.evaluateParallel(helper, spliterator);
	}

	@Override
	public int getOpFlags() {
	return StreamOpFlag.NOT_ORDERED;
	}
	};
	}

	/**
	* Constructs a {@code TerminalOp} that implements a functional reduce on
	* {@code int} values.
	*
	* @param identity the identity for the combining function
	* @param operator the combining function
	* @return a {@code TerminalOp} implementing the reduction
	*/
	public static TerminalOp<Integer, Integer>
	makeInt(int identity, IntBinaryOperator operator) {
	Objects.requireNonNull(operator);
	class ReducingSink
	implements AccumulatingSink<Integer, Integer, ReducingSink>, Sink.OfInt {
	private int state;

	@Override
	public void begin(long size) {
	state = identity;
	}

	@Override
	public void accept(int t) {
	state = operator.applyAsInt(state, t);
	}

	@Override
	public Integer get() {
	return state;
	}

	@Override
	public void combine(ReducingSink other) {
	accept(other.state);
	}
	}
	return new ReduceOp<Integer, Integer, ReducingSink>(StreamShape.INT_VALUE) {
	@Override
	public ReducingSink makeSink() {
	return new ReducingSink();
	}
	};
	}

	/**
	* Constructs a {@code TerminalOp} that implements a functional reduce on
	* {@code int} values, producing an optional integer result.
	*
	* @param operator the combining function
	* @return a {@code TerminalOp} implementing the reduction
	*/
	public static TerminalOp<Integer, OptionalInt>
	makeInt(IntBinaryOperator operator) {
	Objects.requireNonNull(operator);
	class ReducingSink
	implements AccumulatingSink<Integer, OptionalInt, ReducingSink>, Sink.OfInt {
	private boolean empty;
	private int state;

	public void begin(long size) {
	empty = true;
	state = 0;
	}

	@Override
	public void accept(int t) {
	if (empty) {
	empty = false;
	state = t;
	}
	else {
	state = operator.applyAsInt(state, t);
	}
	}

	@Override
	public OptionalInt get() {
	return empty ? OptionalInt.empty() : OptionalInt.of(state);
	}

	@Override
	public void combine(ReducingSink other) {
	if (!other.empty)
	accept(other.state);
	}
	}
	return new ReduceOp<Integer, OptionalInt, ReducingSink>(StreamShape.INT_VALUE) {
	@Override
	public ReducingSink makeSink() {
	return new ReducingSink();
	}
	};
	}

	/**
	* Constructs a {@code TerminalOp} that implements a mutable reduce on
	* {@code int} values.
	*
	* @param <R> The type of the result
	* @param supplier a factory to produce a new accumulator of the result type
	* @param accumulator a function to incorporate an int into an
	* accumulator
	* @param combiner a function to combine an accumulator into another
	* @return A {@code ReduceOp} implementing the reduction
	*/
	public static <R> TerminalOp<Integer, R>
	makeInt(Supplier<R> supplier,
	ObjIntConsumer<R> accumulator,
	BinaryOperator<R> combiner) {
	Objects.requireNonNull(supplier);
	Objects.requireNonNull(accumulator);
	Objects.requireNonNull(combiner);
	class ReducingSink extends Box<R>
	implements AccumulatingSink<Integer, R, ReducingSink>, Sink.OfInt {
	@Override
	public void begin(long size) {
	state = supplier.get();
	}

	@Override
	public void accept(int t) {
	accumulator.accept(state, t);
	}

	@Override
	public void combine(ReducingSink other) {
	state = combiner.apply(state, other.state);
	}
	}
	return new ReduceOp<Integer, R, ReducingSink>(StreamShape.INT_VALUE) {
	@Override
	public ReducingSink makeSink() {
	return new ReducingSink();
	}
	};
	}

	/**
	* Constructs a {@code TerminalOp} that counts the number of stream
	* elements. If the size of the pipeline is known then count is the size
	* and there is no need to evaluate the pipeline. If the size of the
	* pipeline is non known then count is produced, via reduction, using a
	* {@link CountingSink}.
	*
	* @return a {@code TerminalOp} implementing the counting
	*/
	public static TerminalOp<Integer, Long>
	makeIntCounting() {
	return new ReduceOp<Integer, Long, CountingSink<Integer>>(StreamShape.INT_VALUE) {
	@Override
	public CountingSink<Integer> makeSink() { return new CountingSink.OfInt(); }

	@Override
	public <P_IN> Long evaluateSequential(PipelineHelper<Integer> helper,
	Spliterator<P_IN> spliterator) {
	if (StreamOpFlag.SIZED.isKnown(helper.getStreamAndOpFlags()))
	return spliterator.getExactSizeIfKnown();
	return super.evaluateSequential(helper, spliterator);
	}

	@Override
	public <P_IN> Long evaluateParallel(PipelineHelper<Integer> helper,
	Spliterator<P_IN> spliterator) {
	if (StreamOpFlag.SIZED.isKnown(helper.getStreamAndOpFlags()))
	return spliterator.getExactSizeIfKnown();
	return super.evaluateParallel(helper, spliterator);
	}

	@Override
	public int getOpFlags() {
	return StreamOpFlag.NOT_ORDERED;
	}
	};
	}

	/**
	* Constructs a {@code TerminalOp} that implements a functional reduce on
	* {@code long} values.
	*
	* @param identity the identity for the combining function
	* @param operator the combining function
	* @return a {@code TerminalOp} implementing the reduction
	*/
	public static TerminalOp<Long, Long>
	makeLong(long identity, LongBinaryOperator operator) {
	Objects.requireNonNull(operator);
	class ReducingSink
	implements AccumulatingSink<Long, Long, ReducingSink>, Sink.OfLong {
	private long state;

	@Override
	public void begin(long size) {
	state = identity;
	}

	@Override
	public void accept(long t) {
	state = operator.applyAsLong(state, t);
	}

	@Override
	public Long get() {
	return state;
	}

	@Override
	public void combine(ReducingSink other) {
	accept(other.state);
	}
	}
	return new ReduceOp<Long, Long, ReducingSink>(StreamShape.LONG_VALUE) {
	@Override
	public ReducingSink makeSink() {
	return new ReducingSink();
	}
	};
	}

	/**
	* Constructs a {@code TerminalOp} that implements a functional reduce on
	* {@code long} values, producing an optional long result.
	*
	* @param operator the combining function
	* @return a {@code TerminalOp} implementing the reduction
	*/
	public static TerminalOp<Long, OptionalLong>
	makeLong(LongBinaryOperator operator) {
	Objects.requireNonNull(operator);
	class ReducingSink
	implements AccumulatingSink<Long, OptionalLong, ReducingSink>, Sink.OfLong {
	private boolean empty;
	private long state;

	public void begin(long size) {
	empty = true;
	state = 0;
	}

	@Override
	public void accept(long t) {
	if (empty) {
	empty = false;
	state = t;
	}
	else {
	state = operator.applyAsLong(state, t);
	}
	}

	@Override
	public OptionalLong get() {
	return empty ? OptionalLong.empty() : OptionalLong.of(state);
	}

	@Override
	public void combine(ReducingSink other) {
	if (!other.empty)
	accept(other.state);
	}
	}
	return new ReduceOp<Long, OptionalLong, ReducingSink>(StreamShape.LONG_VALUE) {
	@Override
	public ReducingSink makeSink() {
	return new ReducingSink();
	}
	};
	}

	/**
	* Constructs a {@code TerminalOp} that implements a mutable reduce on
	* {@code long} values.
	*
	* @param <R> the type of the result
	* @param supplier a factory to produce a new accumulator of the result type
	* @param accumulator a function to incorporate an int into an
	* accumulator
	* @param combiner a function to combine an accumulator into another
	* @return a {@code TerminalOp} implementing the reduction
	*/
	public static <R> TerminalOp<Long, R>
	makeLong(Supplier<R> supplier,
	ObjLongConsumer<R> accumulator,
	BinaryOperator<R> combiner) {
	Objects.requireNonNull(supplier);
	Objects.requireNonNull(accumulator);
	Objects.requireNonNull(combiner);
	class ReducingSink extends Box<R>
	implements AccumulatingSink<Long, R, ReducingSink>, Sink.OfLong {
	@Override
	public void begin(long size) {
	state = supplier.get();
	}

	@Override
	public void accept(long t) {
	accumulator.accept(state, t);
	}

	@Override
	public void combine(ReducingSink other) {
	state = combiner.apply(state, other.state);
	}
	}
	return new ReduceOp<Long, R, ReducingSink>(StreamShape.LONG_VALUE) {
	@Override
	public ReducingSink makeSink() {
	return new ReducingSink();
	}
	};
	}

	/**
	* Constructs a {@code TerminalOp} that counts the number of stream
	* elements. If the size of the pipeline is known then count is the size
	* and there is no need to evaluate the pipeline. If the size of the
	* pipeline is non known then count is produced, via reduction, using a
	* {@link CountingSink}.
	*
	* @return a {@code TerminalOp} implementing the counting
	*/
	public static TerminalOp<Long, Long>
	makeLongCounting() {
	return new ReduceOp<Long, Long, CountingSink<Long>>(StreamShape.LONG_VALUE) {
	@Override
	public CountingSink<Long> makeSink() { return new CountingSink.OfLong(); }

	@Override
	public <P_IN> Long evaluateSequential(PipelineHelper<Long> helper,
	Spliterator<P_IN> spliterator) {
	if (StreamOpFlag.SIZED.isKnown(helper.getStreamAndOpFlags()))
	return spliterator.getExactSizeIfKnown();
	return super.evaluateSequential(helper, spliterator);
	}

	@Override
	public <P_IN> Long evaluateParallel(PipelineHelper<Long> helper,
	Spliterator<P_IN> spliterator) {
	if (StreamOpFlag.SIZED.isKnown(helper.getStreamAndOpFlags()))
	return spliterator.getExactSizeIfKnown();
	return super.evaluateParallel(helper, spliterator);
	}

	@Override
	public int getOpFlags() {
	return StreamOpFlag.NOT_ORDERED;
	}
	};
	}

	/**
	* Constructs a {@code TerminalOp} that implements a functional reduce on
	* {@code double} values.
	*
	* @param identity the identity for the combining function
	* @param operator the combining function
	* @return a {@code TerminalOp} implementing the reduction
	*/
	public static TerminalOp<Double, Double>
	makeDouble(double identity, DoubleBinaryOperator operator) {
	Objects.requireNonNull(operator);
	class ReducingSink
	implements AccumulatingSink<Double, Double, ReducingSink>, Sink.OfDouble {
	private double state;

	@Override
	public void begin(long size) {
	state = identity;
	}

	@Override
	public void accept(double t) {
	state = operator.applyAsDouble(state, t);
	}

	@Override
	public Double get() {
	return state;
	}

	@Override
	public void combine(ReducingSink other) {
	accept(other.state);
	}
	}
	return new ReduceOp<Double, Double, ReducingSink>(StreamShape.DOUBLE_VALUE) {
	@Override
	public ReducingSink makeSink() {
	return new ReducingSink();
	}
	};
	}

	/**
	* Constructs a {@code TerminalOp} that implements a functional reduce on
	* {@code double} values, producing an optional double result.
	*
	* @param operator the combining function
	* @return a {@code TerminalOp} implementing the reduction
	*/
	public static TerminalOp<Double, OptionalDouble>
	makeDouble(DoubleBinaryOperator operator) {
	Objects.requireNonNull(operator);
	class ReducingSink
	implements AccumulatingSink<Double, OptionalDouble, ReducingSink>, Sink.OfDouble {
	private boolean empty;
	private double state;

	public void begin(long size) {
	empty = true;
	state = 0;
	}

	@Override
	public void accept(double t) {
	if (empty) {
	empty = false;
	state = t;
	}
	else {
	state = operator.applyAsDouble(state, t);
	}
	}

	@Override
	public OptionalDouble get() {
	return empty ? OptionalDouble.empty() : OptionalDouble.of(state);
	}

	@Override
	public void combine(ReducingSink other) {
	if (!other.empty)
	accept(other.state);
	}
	}
	return new ReduceOp<Double, OptionalDouble, ReducingSink>(StreamShape.DOUBLE_VALUE) {
	@Override
	public ReducingSink makeSink() {
	return new ReducingSink();
	}
	};
	}

	/**
	* Constructs a {@code TerminalOp} that implements a mutable reduce on
	* {@code double} values.
	*
	* @param <R> the type of the result
	* @param supplier a factory to produce a new accumulator of the result type
	* @param accumulator a function to incorporate an int into an
	* accumulator
	* @param combiner a function to combine an accumulator into another
	* @return a {@code TerminalOp} implementing the reduction
	*/
	public static <R> TerminalOp<Double, R>
	makeDouble(Supplier<R> supplier,
	ObjDoubleConsumer<R> accumulator,
	BinaryOperator<R> combiner) {
	Objects.requireNonNull(supplier);
	Objects.requireNonNull(accumulator);
	Objects.requireNonNull(combiner);
	class ReducingSink extends Box<R>
	implements AccumulatingSink<Double, R, ReducingSink>, Sink.OfDouble {
	@Override
	public void begin(long size) {
	state = supplier.get();
	}

	@Override
	public void accept(double t) {
	accumulator.accept(state, t);
	}

	@Override
	public void combine(ReducingSink other) {
	state = combiner.apply(state, other.state);
	}
	}
	return new ReduceOp<Double, R, ReducingSink>(StreamShape.DOUBLE_VALUE) {
	@Override
	public ReducingSink makeSink() {
	return new ReducingSink();
	}
	};
	}

	/**
	* Constructs a {@code TerminalOp} that counts the number of stream
	* elements. If the size of the pipeline is known then count is the size
	* and there is no need to evaluate the pipeline. If the size of the
	* pipeline is non known then count is produced, via reduction, using a
	* {@link CountingSink}.
	*
	* @return a {@code TerminalOp} implementing the counting
	*/
	public static TerminalOp<Double, Long>
	makeDoubleCounting() {
	return new ReduceOp<Double, Long, CountingSink<Double>>(StreamShape.DOUBLE_VALUE) {
	@Override
	public CountingSink<Double> makeSink() { return new CountingSink.OfDouble(); }

	@Override
	public <P_IN> Long evaluateSequential(PipelineHelper<Double> helper,
	Spliterator<P_IN> spliterator) {
	if (StreamOpFlag.SIZED.isKnown(helper.getStreamAndOpFlags()))
	return spliterator.getExactSizeIfKnown();
	return super.evaluateSequential(helper, spliterator);
	}

	@Override
	public <P_IN> Long evaluateParallel(PipelineHelper<Double> helper,
	Spliterator<P_IN> spliterator) {
	if (StreamOpFlag.SIZED.isKnown(helper.getStreamAndOpFlags()))
	return spliterator.getExactSizeIfKnown();
	return super.evaluateParallel(helper, spliterator);
	}

	@Override
	public int getOpFlags() {
	return StreamOpFlag.NOT_ORDERED;
	}
	};
	}

	/**
	* A sink that counts elements
	*/
	abstract static class CountingSink<T>
	extends Box<Long>
	implements AccumulatingSink<T, Long, CountingSink<T>> {
	long count;

	@Override
	public void begin(long size) {
	count = 0L;
	}

	@Override
	public Long get() {
	return count;
	}

	@Override
	public void combine(CountingSink<T> other) {
	count += other.count;
	}

	static final class OfRef<T> extends CountingSink<T> {
	@Override
	public void accept(T t) {
	count++;
	}
	}

	static final class OfInt extends CountingSink<Integer> implements Sink.OfInt {
	@Override
	public void accept(int t) {
	count++;
	}
	}

	static final class OfLong extends CountingSink<Long> implements Sink.OfLong {
	@Override
	public void accept(long t) {
	count++;
	}
	}

	static final class OfDouble extends CountingSink<Double> implements Sink.OfDouble {
	@Override
	public void accept(double t) {
	count++;
	}
	}
	}

	/**
	* A type of {@code TerminalSink} that implements an associative reducing
	* operation on elements of type {@code T} and producing a result of type
	* {@code R}.
	*
	* @param <T> the type of input element to the combining operation
	* @param <R> the result type
	* @param <K> the type of the {@code AccumulatingSink}.
	*/
	private interface AccumulatingSink<T, R, K extends AccumulatingSink<T, R, K>>
	extends TerminalSink<T, R> {
	void combine(K other);
	}

	/**
	* State box for a single state element, used as a base class for
	* {@code AccumulatingSink} instances
	*
	* @param <U> The type of the state element
	*/
	private abstract static class Box<U> {
	U state;

	Box() {} // Avoid creation of special accessor

	public U get() {
	return state;
	}
	}

	/**
	* A {@code TerminalOp} that evaluates a stream pipeline and sends the
	* output into an {@code AccumulatingSink}, which performs a reduce
	* operation. The {@code AccumulatingSink} must represent an associative
	* reducing operation.
	*
	* @param <T> the output type of the stream pipeline
	* @param <R> the result type of the reducing operation
	* @param <S> the type of the {@code AccumulatingSink}
	*/
	private abstract static class ReduceOp<T, R, S extends AccumulatingSink<T, R, S>>
	implements TerminalOp<T, R> {
	private final StreamShape inputShape;

	/**
	* Create a {@code ReduceOp} of the specified stream shape which uses
	* the specified {@code Supplier} to create accumulating sinks.
	*
	* @param shape The shape of the stream pipeline
	*/
	ReduceOp(StreamShape shape) {
	inputShape = shape;
	}

	public abstract S makeSink();

	@Override
	public StreamShape inputShape() {
	return inputShape;
	}

	@Override
	public <P_IN> R evaluateSequential(PipelineHelper<T> helper,
	Spliterator<P_IN> spliterator) {
	return helper.wrapAndCopyInto(makeSink(), spliterator).get();
	}

	@Override
	public <P_IN> R evaluateParallel(PipelineHelper<T> helper,
	Spliterator<P_IN> spliterator) {
	return new ReduceTask<>(this, helper, spliterator).invoke().get();
	}
	}

	/**
	* A {@code ForkJoinTask} for performing a parallel reduce operation.
	*/
	@SuppressWarnings("serial")
	private static final class ReduceTask<P_IN, P_OUT, R,
	S extends AccumulatingSink<P_OUT, R, S>>
	extends AbstractTask<P_IN, P_OUT, S, ReduceTask<P_IN, P_OUT, R, S>> {
	private final ReduceOp<P_OUT, R, S> op;

	ReduceTask(ReduceOp<P_OUT, R, S> op,
	PipelineHelper<P_OUT> helper,
	Spliterator<P_IN> spliterator) {
	super(helper, spliterator);
	this.op = op;
	}

	ReduceTask(ReduceTask<P_IN, P_OUT, R, S> parent,
	Spliterator<P_IN> spliterator) {
	super(parent, spliterator);
	this.op = parent.op;
	}

	@Override
	protected ReduceTask<P_IN, P_OUT, R, S> makeChild(Spliterator<P_IN> spliterator) {
	return new ReduceTask<>(this, spliterator);
	}

	@Override
	protected S doLeaf() {
	return helper.wrapAndCopyInto(op.makeSink(), spliterator);
	}

	@Override
	public void onCompletion(CountedCompleter<?> caller) {
	if (!isLeaf()) {
	S leftResult = leftChild.getLocalResult();
	leftResult.combine(rightChild.getLocalResult());
	setLocalResult(leftResult);
	}
	// GC spliterator, left and right child
	super.onCompletion(caller);
	}
	}
	}

Back to index...