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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);
 }

 /**
 * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
 * and <em>fail-fast</em> {@code Spliterator} over the elements in this set.
 *
 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
 * {@link Spliterator#DISTINCT}, and {@code ORDERED}. Implementations
 * should document the reporting of additional characteristic values.
 *
 * @implNote
 * The implementation creates a
 * <em><a href="Spliterator.html#binding">late-binding</a></em> spliterator
 * from the set's {@code Iterator}. The spliterator inherits the
 * <em>fail-fast</em> properties of the set's iterator.
 * The created {@code Spliterator} additionally reports
 * {@link Spliterator#SUBSIZED}.
 *
 * @return a {@code Spliterator} over the elements in this set
 * @since 1.8
 */
 @Override
 public Spliterator<E> spliterator() {
 return Spliterators.spliterator(this, Spliterator.DISTINCT | Spliterator.ORDERED);
 }
}