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	/*
	* Licensed to the Apache Software Foundation (ASF) under one or more
	* contributor license agreements. See the NOTICE file distributed with
	* this work for additional information regarding copyright ownership.
	* The ASF licenses this file to You under the Apache License, Version 2.0
	* (the "License"); you may not use this file except in compliance with
	* the License. You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/
	package org.apache.commons.lang3.stream;

	import java.lang.reflect.Array;
	import java.util.ArrayList;
	import java.util.Collection;
	import java.util.Collections;
	import java.util.List;
	import java.util.Set;
	import java.util.function.BiConsumer;
	import java.util.function.BinaryOperator;
	import java.util.function.Consumer;
	import java.util.function.Function;
	import java.util.function.Predicate;
	import java.util.function.Supplier;
	import java.util.stream.Collector;
	import java.util.stream.Collectors;
	import java.util.stream.Stream;

	import org.apache.commons.lang3.function.Failable;
	import org.apache.commons.lang3.function.FailableConsumer;
	import org.apache.commons.lang3.function.FailableFunction;
	import org.apache.commons.lang3.function.FailablePredicate;

	/**
	* Provides utility functions, and classes for working with the
	* {@code java.util.stream} package, or more generally, with Java 8 lambdas. More
	* specifically, it attempts to address the fact that lambdas are supposed
	* not to throw Exceptions, at least not checked Exceptions, AKA instances
	* of {@link Exception}. This enforces the use of constructs like
	* <pre>
	* Consumer<java.lang.reflect.Method> consumer = (m) -> {
	* try {
	* m.invoke(o, args);
	* } catch (Throwable t) {
	* throw Failable.rethrow(t);
	* }
	* };
	* stream.forEach(consumer);
	* </pre>
	* Using a {@link FailableStream}, this can be rewritten as follows:
	* <pre>
	* Streams.failable(stream).forEach((m) -> m.invoke(o, args));
	* </pre>
	* Obviously, the second version is much more concise and the spirit of
	* Lambda expressions is met better than in the first version.
	*
	* @see Stream
	* @see Failable
	* @since 3.11
	*/
	public class Streams {

	public static class ArrayCollector<O> implements Collector<O, List<O>, O[]> {
	private static final Set<Characteristics> characteristics = Collections.emptySet();
	private final Class<O> elementType;

	public ArrayCollector(final Class<O> elementType) {
	this.elementType = elementType;
	}

	@Override
	public BiConsumer<List<O>, O> accumulator() {
	return List::add;
	}

	@Override
	public Set<Characteristics> characteristics() {
	return characteristics;
	}

	@Override
	public BinaryOperator<List<O>> combiner() {
	return (left, right) -> {
	left.addAll(right);
	return left;
	};
	}

	@Override
	public Function<List<O>, O[]> finisher() {
	return list -> {
	@SuppressWarnings("unchecked")
	final O[] array = (O[]) Array.newInstance(elementType, list.size());
	return list.toArray(array);
	};
	}

	@Override
	public Supplier<List<O>> supplier() {
	return ArrayList::new;
	}
	}

	/**
	* A reduced, and simplified version of a {@link Stream} with failable method signatures.
	*
	* @param <O> The streams element type.
	*/
	public static class FailableStream<O extends Object> {

	private Stream<O> stream;
	private boolean terminated;

	/**
	* Constructs a new instance with the given {@code stream}.
	*
	* @param stream The stream.
	*/
	public FailableStream(final Stream<O> stream) {
	this.stream = stream;
	}

	/**
	* 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 short-circuiting terminal operation.
	*
	* Note 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 non-interfering, stateless 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}.
	*/
	public boolean allMatch(final FailablePredicate<O, ?> predicate) {
	assertNotTerminated();
	return stream().allMatch(Failable.asPredicate(predicate));
	}

	/**
	* 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 short-circuiting terminal operation.
	*
	* Note 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 non-interfering, stateless predicate to apply to elements of this stream
	* @return {@code true} if any elements of the stream match the provided predicate, otherwise {@code false}
	*/
	public boolean anyMatch(final FailablePredicate<O, ?> predicate) {
	assertNotTerminated();
	return stream().anyMatch(Failable.asPredicate(predicate));
	}

	protected void assertNotTerminated() {
	if (terminated) {
	throw new IllegalStateException("This stream is already terminated.");
	}
	}

	/**
	* Performs a mutable reduction 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 underlying stream is parallel, and the {@code Collector} is concurrent, and either the stream is
	* unordered or the collector is unordered, then a concurrent reduction will be performed (see {@link Collector}
	* for details on concurrent reduction.)
	*
	* <p>
	* This is a terminal operation.
	*
	* <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.
	*
	* Note 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
	*/
	public <A, R> R collect(final Collector<? super O, A, R> collector) {
	makeTerminated();
	return stream().collect(collector);
	}

	/**
	* Performs a mutable reduction operation on the elements of this FailableStream. 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 terminal operation.
	*
	* Note 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> type of the result
	* @param <A> Type of the accumulator.
	* @param pupplier 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 associative, non-interfering, stateless function for incorporating an additional
	* element into a result
	* @param combiner An associative, non-interfering, stateless function for combining two values, which must be
	* compatible with the accumulator function
	* @return The result of the reduction
	*/
	public <A, R> R collect(final Supplier<R> pupplier, final BiConsumer<R, ? super O> accumulator,
	final BiConsumer<R, R> combiner) {
	makeTerminated();
	return stream().collect(pupplier, accumulator, combiner);
	}

	/**
	* Returns a FailableStream consisting of the elements of this stream that match the given FailablePredicate.
	*
	* <p>
	* This is an intermediate operation.
	*
	* @param predicate a non-interfering, stateless predicate to apply to each element to determine if it should be
	* included.
	* @return the new stream
	*/
	public FailableStream<O> filter(final FailablePredicate<O, ?> predicate) {
	assertNotTerminated();
	stream = stream.filter(Failable.asPredicate(predicate));
	return this;
	}

	/**
	* Performs an action for each element of this stream.
	*
	* <p>
	* This is a terminal operation.
	*
	* <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 non-interfering action to perform on the elements
	*/
	public void forEach(final FailableConsumer<O, ?> action) {
	makeTerminated();
	stream().forEach(Failable.asConsumer(action));
	}

	protected void makeTerminated() {
	assertNotTerminated();
	terminated = true;
	}

	/**
	* Returns a stream consisting of the results of applying the given function to the elements of this stream.
	*
	* <p>
	* This is an intermediate operation.
	*
	* @param <R> The element type of the new stream
	* @param mapper A non-interfering, stateless function to apply to each element
	* @return the new stream
	*/
	public <R> FailableStream<R> map(final FailableFunction<O, R, ?> mapper) {
	assertNotTerminated();
	return new FailableStream<>(stream.map(Failable.asFunction(mapper)));
	}

	/**
	* Performs a reduction on the elements of this stream, using the provided identity value and an associative
	* accumulation function, and returns the reduced value. This is equivalent to:
	*
	* <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 associative function.
	*
	* <p>
	* This is a terminal operation.
	*
	* Note 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 associative, non-interfering, stateless function for combining two values
	* @return the result of the reduction
	*/
	public O reduce(final O identity, final BinaryOperator<O> accumulator) {
	makeTerminated();
	return stream().reduce(identity, accumulator);
	}

	/**
	* Converts the FailableStream into an equivalent stream.
	*
	* @return A stream, which will return the same elements, which this FailableStream would return.
	*/
	public Stream<O> stream() {
	return stream;
	}
	}

	/**
	* Converts the given {@link Collection} into a {@link FailableStream}. This is basically a simplified, reduced
	* version of the {@link Stream} class, with the same underlying element stream, except that failable objects, like
	* {@link FailablePredicate}, {@link FailableFunction}, or {@link FailableConsumer} may be applied, instead of
	* {@link Predicate}, {@link Function}, or {@link Consumer}. The idea is to rewrite a code snippet like this:
	*
	* <pre>
	* final List<O> list;
	* final Method m;
	* final Function<O, String> mapper = (o) -> {
	* try {
	* return (String) m.invoke(o);
	* } catch (Throwable t) {
	* throw Failable.rethrow(t);
	* }
	* };
	* final List<String> strList = list.stream().map(mapper).collect(Collectors.toList());
	* </pre>
	*
	* as follows:
	*
	* <pre>
	* final List<O> list;
	* final Method m;
	* final List<String> strList = Failable.stream(list.stream()).map((o) -> (String) m.invoke(o))
	* .collect(Collectors.toList());
	* </pre>
	*
	* While the second version may not be <em>quite</em> as efficient (because it depends on the creation of
	* additional, intermediate objects, of type FailableStream), it is much more concise, and readable, and meets the
	* spirit of Lambdas better than the first version.
	*
	* @param <O> The streams element type.
	* @param stream The stream, which is being converted.
	* @return The {@link FailableStream}, which has been created by converting the stream.
	*/
	public static <O> FailableStream<O> stream(final Collection<O> stream) {
	return stream(stream.stream());
	}

	/**
	* Converts the given {@link Stream stream} into a {@link FailableStream}. This is basically a simplified, reduced
	* version of the {@link Stream} class, with the same underlying element stream, except that failable objects, like
	* {@link FailablePredicate}, {@link FailableFunction}, or {@link FailableConsumer} may be applied, instead of
	* {@link Predicate}, {@link Function}, or {@link Consumer}. The idea is to rewrite a code snippet like this:
	*
	* <pre>
	* final List<O> list;
	* final Method m;
	* final Function<O, String> mapper = (o) -> {
	* try {
	* return (String) m.invoke(o);
	* } catch (Throwable t) {
	* throw Failable.rethrow(t);
	* }
	* };
	* final List<String> strList = list.stream().map(mapper).collect(Collectors.toList());
	* </pre>
	*
	* as follows:
	*
	* <pre>
	* final List<O> list;
	* final Method m;
	* final List<String> strList = Failable.stream(list.stream()).map((o) -> (String) m.invoke(o))
	* .collect(Collectors.toList());
	* </pre>
	*
	* While the second version may not be <em>quite</em> as efficient (because it depends on the creation of
	* additional, intermediate objects, of type FailableStream), it is much more concise, and readable, and meets the
	* spirit of Lambdas better than the first version.
	*
	* @param <O> The streams element type.
	* @param stream The stream, which is being converted.
	* @return The {@link FailableStream}, which has been created by converting the stream.
	*/
	public static <O> FailableStream<O> stream(final Stream<O> stream) {
	return new FailableStream<>(stream);
	}

	/**
	* Returns a {@code Collector} that accumulates the input elements into a new array.
	*
	* @param pElementType Type of an element in the array.
	* @param <O> the type of the input elements
	* @return a {@code Collector} which collects all the input elements into an array, in encounter order
	*/
	public static <O extends Object> Collector<O, ?, O[]> toArray(final Class<O> pElementType) {
	return new ArrayCollector<>(pElementType);
	}
	}

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