/*

 * Copyright 2000-2006 Sun Microsystems, Inc.  All Rights Reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package java.util;

/**

 * <p>Hash table and linked list implementation of the <tt>Set</tt> interface,

 * with predictable iteration order.  This implementation differs from

 * <tt>HashSet</tt> in that it maintains a doubly-linked list running through

 * all of its entries.  This linked list defines the iteration ordering,

 * which is the order in which elements were inserted into the set

 * (<i>insertion-order</i>).  Note that insertion order is <i>not</i> affected

 * if an element is <i>re-inserted</i> into the set.  (An element <tt>e</tt>

 * is reinserted into a set <tt>s</tt> if <tt>s.add(e)</tt> is invoked when

 * <tt>s.contains(e)</tt> would return <tt>true</tt> immediately prior to

 * the invocation.)

 *

 * <p>This implementation spares its clients from the unspecified, generally

 * chaotic ordering provided by {@link HashSet}, without incurring the

 * increased cost associated with {@link TreeSet}.  It can be used to

 * produce a copy of a set that has the same order as the original, regardless

 * of the original set's implementation:

 * <pre>

 *     void foo(Set s) {

 *         Set copy = new LinkedHashSet(s);

 *         ...

 *     }

 * </pre>

 * This technique is particularly useful if a module takes a set on input,

 * copies it, and later returns results whose order is determined by that of

 * the copy.  (Clients generally appreciate having things returned in the same

 * order they were presented.)

 *

 * <p>This class provides all of the optional <tt>Set</tt> operations, and

 * permits null elements.  Like <tt>HashSet</tt>, it provides constant-time

 * performance for the basic operations (<tt>add</tt>, <tt>contains</tt> and

 * <tt>remove</tt>), assuming the hash function disperses elements

 * properly among the buckets.  Performance is likely to be just slightly

 * below that of <tt>HashSet</tt>, due to the added expense of maintaining the

 * linked list, with one exception: Iteration over a <tt>LinkedHashSet</tt>

 * requires time proportional to the <i>size</i> of the set, regardless of

 * its capacity.  Iteration over a <tt>HashSet</tt> is likely to be more

 * expensive, requiring time proportional to its <i>capacity</i>.

 *

 * <p>A linked hash set has two parameters that affect its performance:

 * <i>initial capacity</i> and <i>load factor</i>.  They are defined precisely

 * as for <tt>HashSet</tt>.  Note, however, that the penalty for choosing an

 * excessively high value for initial capacity is less severe for this class

 * than for <tt>HashSet</tt>, as iteration times for this class are unaffected

 * by capacity.

 *

 * <p><strong>Note that this implementation is not synchronized.</strong>

 * If multiple threads access a linked hash set concurrently, and at least

 * one of the threads modifies the set, it <em>must</em> be synchronized

 * externally.  This is typically accomplished by synchronizing on some

 * object that naturally encapsulates the set.

 *

 * If no such object exists, the set should be "wrapped" using the

 * {@link Collections#synchronizedSet Collections.synchronizedSet}

 * method.  This is best done at creation time, to prevent accidental

 * unsynchronized access to the set: <pre>

 *   Set s = Collections.synchronizedSet(new LinkedHashSet(...));</pre>

 *

 * <p>The iterators returned by this class's <tt>iterator</tt> method are

 * <em>fail-fast</em>: if the set is modified at any time after the iterator

 * is created, in any way except through the iterator's own <tt>remove</tt>

 * method, the iterator will throw a {@link ConcurrentModificationException}.

 * Thus, in the face of concurrent modification, the iterator fails quickly

 * and cleanly, rather than risking arbitrary, non-deterministic behavior at

 * an undetermined time in the future.

 *

 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed

 * as it is, generally speaking, impossible to make any hard guarantees in the

 * presence of unsynchronized concurrent modification.  Fail-fast iterators

 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.

 * Therefore, it would be wrong to write a program that depended on this

 * exception for its correctness:   <i>the fail-fast behavior of iterators

 * should be used only to detect bugs.</i>

 *

 * <p>This class is a member of the

 * <a href="{@docRoot}/../technotes/guides/collections/index.html">

 * Java Collections Framework</a>.

 *

 * @param <E> the type of elements maintained by this set

 *

 * @author  Josh Bloch

 * @see     Object#hashCode()

 * @see     Collection

 * @see     Set

 * @see     HashSet

 * @see     TreeSet

 * @see     Hashtable

 * @since   1.4

 */

public class LinkedHashSet<E>

    extends HashSet<E>

    implements Set<E>, Cloneable, java.io.Serializable {

    private static final long serialVersionUID = -2851667679971038690L;

    /**

     * Constructs a new, empty linked hash set with the specified initial

     * capacity and load factor.

     *

     * @param      initialCapacity the initial capacity of the linked hash set

     * @param      loadFactor      the load factor of the linked hash set

     * @throws     IllegalArgumentException  if the initial capacity is less

     *               than zero, or if the load factor is nonpositive

     */

    public LinkedHashSet(int initialCapacity, float loadFactor) {

        super(initialCapacity, loadFactor, true);

    }

    /**

     * Constructs a new, empty linked hash set with the specified initial

     * capacity and the default load factor (0.75).

     *

     * @param   initialCapacity   the initial capacity of the LinkedHashSet

     * @throws  IllegalArgumentException if the initial capacity is less

     *              than zero

     */

    public LinkedHashSet(int initialCapacity) {

        super(initialCapacity, .75f, true);

    }

    /**

     * Constructs a new, empty linked hash set with the default initial

     * capacity (16) and load factor (0.75).

     */

    public LinkedHashSet() {

        super(16, .75f, true);

    }

    /**

     * Constructs a new linked hash set with the same elements as the

     * specified collection.  The linked hash set is created with an initial

     * capacity sufficient to hold the elements in the specified collection

     * and the default load factor (0.75).

     *

     * @param c  the collection whose elements are to be placed into

     *           this set

     * @throws NullPointerException if the specified collection is null

     */

    public LinkedHashSet(Collection<? extends E> c) {

        super(Math.max(2*c.size(), 11), .75f, true);

        addAll(c);

    }

}