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Almost Functional is very low impact functional classes inspired by guava, jdk 1.8 and various others.

There is a newer version: 1.8

/*
 * Copyright (c) 2013-2014, [email protected]
 *
 * Permission to use, copy, modify, and/or distribute this software for any purpose with or
 * without fee is hereby granted, provided that the above copyright notice and this permission
 * notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO
 * THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR
 * ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF
 * CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE
 * OR PERFORMANCE OF THIS SOFTWARE.
 */

package almost.functional.utils;

import almost.functional.Optional;
import almost.functional.Supplier;

import java.util.Iterator;
import java.util.NoSuchElementException;

import static almost.functional.utils.Preconditions.checkNotNull;

/**
 * Creates an Iterable from any Supplier of Optionals. The resulting Iterator hasNext until the
 * Supplier returns and empty Optional.
 * @param  type of the Iterable and the Suppliers Optional
 */
public class SupplierIterable implements Iterable {
	private final Supplier> supplier;

	/**
	 * Constructor accepting the Supplier. Supplier must return non null Optionals.
	 * @param supplier a Supplier of Optionals of type T
	 */
	public SupplierIterable(Supplier> supplier) {
		checkNotNull(supplier, "Supplier must not be null");
		this.supplier = supplier;
	}

	@Override
	public Iterator iterator() {
		return new ImmutableIterator() {
			private Optional next = null;

			@Override
			public boolean hasNext() {
                if (next == null) {
                    next = supplier.get();
                    checkNotNull(next, "supplier returned null");
                }
                return next.isPresent();
			}

			@Override
			public T next() {
				if (!hasNext()) {
					throw new NoSuchElementException("next invoke on iterator where hasNext is false.");
				}
				T value = next.get();
				next = null;
				return value;
			}
		};
	}
}