/*
 * $Id$
 * This file is a part of the Arakhne Foundation Classes, http://www.arakhne.org/afc
 *
 * Copyright (c) 2000-2012 Stephane GALLAND.
 * Copyright (c) 2005-10, Multiagent Team, Laboratoire Systemes et Transports,
 *                        Universite de Technologie de Belfort-Montbeliard.
 * Copyright (c) 2013-2016 The original authors, and other authors.
 *
 * 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.arakhne.afc.references;

import java.lang.ref.WeakReference;
import java.util.Collection;
import java.util.HashSet;
import java.util.WeakHashMap;

/**
 * A <tt>Set</tt> implementation with {@link WeakReference weak values}. An entry in a
 * <tt>WeakHashSet</tt> will automatically be removed when its value is no
 * longer in ordinary use or null.
 *
 * <p>This class was inspirated from {@link WeakHashMap} and uses a {@link HashSet}
 * as its internal data structure.
 *
 * <p>This class has a special flag which permits to control the
 * way how the released references are expurged: {@link #isDeeplyExpurge()},
 * {@link #setDeeplyExpurge(boolean)}. If this flag is <code>true</code>,
 * all the released references will be immediately removed from the map even
 * if they are not enqueued by the virtual machine (see {@link #expurge()}.
 * If this flag is <code>false</code>,
 * only the enqueued references will be removed from the map
 * (see {@link #expurgeQueuedReferences()}.
 *
 * <p>If this map does not use a "deep expurge" of the released references,
 * it could contains <code>null</code> values that corresponds to
 * values that are released by the garbage collector. If a "deep expurge"
 * is used, all the values released by the garbage collector will be
 * removed from the map.
 *
 * <p>"Deep expurge" consumes much more time that "No deep expurge". This is the
 * reason why this feature is not activated by default.
 *
 * <p>The "deep expurge" feature was added to fix the uncoherent behavior
 * of the garbage collector which seems to not always enqueued the
 * released values (sometimes the queue is empty even if a value was released).
 *
 * @param <E> is the type of the values.
 * @author $Author: sgalland$
 * @version $FullVersion$
 * @mavengroupid $GroupId$
 * @mavenartifactid $ArtifactId$
 * @since 5.9
 */
public class WeakHashSet<E> extends AbstractReferencedSet<E, WeakReference<E>> {

	/**
	 * Constructs an empty <tt>HashSet</tt>.
	 */
	public WeakHashSet() {
		super(new HashSet<WeakReference<E>>(), WeakReference.class);
	}

	/**
	 * Constructs a new, empty set; the backing <tt>HashSet</tt> instance has
	 * the specified initial capacity and default load factor (0.75).
	 *
	 * @param      initialCapacity   the initial capacity of the hash table
	 * @throws     IllegalArgumentException if the initial capacity is less
	 *             than zero
	 */
	public WeakHashSet(int initialCapacity) {
		super(new HashSet<WeakReference<E>>(initialCapacity), WeakReference.class);
	}

	/**
	 * Constructs a new, empty set; the backing <tt>HashSet</tt> instance has
	 * the specified initial capacity and the specified load factor.
	 *
	 * @param      initialCapacity   the initial capacity of the hash map
	 * @param      loadFactor        the load factor of the hash map
	 * @throws     IllegalArgumentException if the initial capacity is less
	 *             than zero, or if the load factor is nonpositive
	 */
	public WeakHashSet(int initialCapacity, float loadFactor) {
		super(new HashSet<WeakReference<E>>(initialCapacity, loadFactor), WeakReference.class);
	}

	/**
	 * Constructs a new set containing the elements in the specified
	 * collection.  The <tt>HashSet</tt> is created with default load factor
	 * (0.75) and an initial capacity sufficient to contain the elements in
	 * the specified collection.
	 *
	 * @param collection the collection whose elements are to be placed into this set
	 * @throws NullPointerException if the specified collection is null
	 */
	public WeakHashSet(Collection<? extends E> collection) {
		super(new HashSet<WeakReference<E>>(), WeakReference.class);
		addAll(collection);
	}

	@Override
	protected final WeakReference<E> createReference(E element) {
		return new WeakReference<>(element);
	}

}