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Implementation Maybe monad in Java

There is a newer version: 1.1.0

/*
 * Copyright (c) 2015-2016, Ivan Sokolov. All rights reserved.
 * This code is licensed under MIT license (see LICENSE for details)
 */

package com.github.sirikid.iterators;

import java.util.Spliterator;
import java.util.function.Consumer;
import javax.annotation.Nullable;

import static java.util.Objects.requireNonNull;

/**
 * Spliterator, that contains only one element.
 *
 * @author Ivan Sokolov
 * @version 1.0.0
 * @param  type of element
 * @see SingletonIterator
 * @since 1.0.0
 */

public class SingletonSpliterator implements Spliterator {
	@Nullable private final T value;
	private boolean alreadyUsed;

	/**
	 * Sole constructor.
	 *
	 * @param value the value to be in spliterator
	 */
	public SingletonSpliterator(@Nullable T value) {
		this.value = value;
		alreadyUsed = false;
	}

	/** {@inheritDoc} */
	@Override
	public boolean tryAdvance(Consumer action) {
		requireNonNull(action);
		if (!alreadyUsed) {
			action.accept(value);
//			value = null; // See line 48 in SingletonIterator.java
			alreadyUsed = true;
			return true;
		}
		return false;
	}

	/** {@inheritDoc} */
	@Nullable
	@Override
	public Spliterator trySplit() {
		return null;
	}

	/** {@inheritDoc} */
	@Override
	public long estimateSize() {
		return alreadyUsed ? 0 : 1;
	}

	/** {@inheritDoc} */
	@Override
	public int characteristics() {
		return DISTINCT | SIZED | SUBSIZED | IMMUTABLE;
	}
}