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A lightweight alternative to Java 8 sequential Stream
There is a newer version: 2.3.0
/*
 * Copyright 2016 Daniel Skogquist Åborg
 *
 * Licensed 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.d2ab.iterable;

import org.d2ab.collection.Maps;
import org.d2ab.iterator.ArrayIterator;
import org.d2ab.util.Pair;

import java.util.*;
import java.util.function.Predicate;
import java.util.stream.Stream;

/**
 * Utility methods for {@link Iterable} instances.
 */
public class Iterables {
	private Iterables() {
	}

	/**
	 * @return an {@link Iterable} containing the given objects.
	 */
	@SafeVarargs
	public static  Iterable of(T... objects) {
		return () -> new ArrayIterator<>(objects);
	}

	/**
	 * @return a once-only {@link Iterable} over the given {@link Iterator}, after which the iterable will be empty.
	 */
	public static  Iterable once(Iterator iterator) {
		return () -> iterator;
	}

	/**
	 * Converts a container of some kind into a possibly once-only {@link Iterable}.
	 *
	 * @param container the non-null container to turn into an {@link Iterable}, can be one of {@link Iterable}, {@link
	 *                  Iterator}, {@link Stream}, {@code Array}, {@link Pair} or {@link Map.Entry}.
	 *
	 * @return the container as an iterable.
	 *
	 * @throws ClassCastException if the container is not one of {@link Iterable}, {@link Iterator}, {@link Stream},
	 *                            {@code Array}, {@link Pair} or {@link Map.Entry}
	 */
	@SuppressWarnings("unchecked")
	public static  Iterable from(Object container) {
		if (container instanceof Iterable)
			return (Iterable) container;
		else if (container instanceof Iterator)
			return once((Iterator) container);
		else if (container instanceof Stream)
			return once(((Stream) container).iterator());
		else if (container instanceof Object[])
			return of((T[]) container);
		else if (container instanceof Pair)
			return ((Pair) container)::iterator;
		else if (container instanceof Map.Entry)
			return () -> Maps.iterator((Map.Entry) container);
		else
			throw new ClassCastException(
					"Required an Iterable, Iterator, Array, Stream, Pair or Entry but got: " + container.getClass());
	}

	/**
	 * @return true if all elements in this {@code Sequence} satisfy the given predicate, false otherwise.
	 */
	public static  boolean all(Iterable iterable, Predicate predicate) {
		for (T each : iterable) {
			if (!predicate.test(each))
				return false;
		}
		return true;
	}

	/**
	 * @return true if no elements in this {@code Sequence} satisfy the given predicate, false otherwise.
	 */
	public static  boolean none(Iterable iterable, Predicate predicate) {
		return !any(iterable, predicate);
	}

	/**
	 * @return true if any element in this {@code Sequence} satisfies the given predicate, false otherwise.
	 */
	public static  boolean any(Iterable iterable, Predicate predicate) {
		for (T each : iterable) {
			if (predicate.test(each))
				return true;
		}
		return false;
	}

	/**
	 * Remove all elements in the given {@link Iterable} using {@link Iterator#remove()}.
	 */
	public static  void removeAll(Iterable iterable) {
		for (Iterator iterator = iterable.iterator(); iterator.hasNext(); ) {
			iterator.next();
			iterator.remove();
		}
	}

	/**
	 * @return the given {@link Iterable} collected into a {@link List}.
	 */
	public static  List toList(Iterable iterable) {
		List list = new ArrayList<>();
		if (iterable instanceof Collection)
			list.addAll((Collection) iterable);
		else
			iterable.forEach(list::add);
		return list;
	}
}