| /* |
| * Copyright (c) 2000, 2023, Oracle and/or its affiliates. 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. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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| * questions. |
| */ |
| |
| package java.util; |
| |
| /** |
| * <p>Hash table and linked list implementation of the {@code Set} interface, |
| * with well-defined encounter order. This implementation differs from |
| * {@code HashSet} in that it maintains a doubly-linked list running through |
| * all of its entries. This linked list defines the encounter order (iteration |
| * order), which is the order in which elements were inserted into the set |
| * (<i>insertion-order</i>). The least recently inserted element (the eldest) is |
| * first, and the youngest element is last. Note that encounter order is <i>not</i> affected |
| * if an element is <i>re-inserted</i> into the set with the {@code add} method. |
| * (An element {@code e} is reinserted into a set {@code s} if {@code s.add(e)} is |
| * invoked when {@code s.contains(e)} would return {@code true} immediately prior to |
| * the invocation.) The reverse-ordered view of this set is in the opposite order, with |
| * the youngest element appearing first and the eldest element appearing last. The encounter |
| * order of elements already in the set can be changed by using the |
| * {@link #addFirst addFirst} and {@link #addLast addLast} methods. |
| * |
| * <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>{@code |
| * void foo(Set<String> s) { |
| * Set<String> 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 {@link Set} and {@link SequencedSet} |
| * operations, and it permits null elements. Like {@code HashSet}, it provides constant-time |
| * performance for the basic operations ({@code add}, {@code contains} and |
| * {@code remove}), assuming the hash function disperses elements |
| * properly among the buckets. Performance is likely to be just slightly |
| * below that of {@code HashSet}, due to the added expense of maintaining the |
| * linked list, with one exception: Iteration over a {@code LinkedHashSet} |
| * requires time proportional to the <i>size</i> of the set, regardless of |
| * its capacity. Iteration over a {@code HashSet} 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 {@code HashSet}. Note, however, that the penalty for choosing an |
| * excessively high value for initial capacity is less severe for this class |
| * than for {@code HashSet}, 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 {@code iterator} 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 {@code remove} |
| * 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 {@code ConcurrentModificationException} 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}/java.base/java/util/package-summary.html#CollectionsFramework"> |
| * 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 SequencedSet<E>, Set<E>, Cloneable, java.io.Serializable { |
| |
| @java.io.Serial |
| private static final long serialVersionUID = -2851667679971038690L; |
| |
| /** |
| * Constructs a new, empty linked hash set with the specified initial |
| * capacity and load factor. |
| * |
| * @apiNote |
| * To create a {@code LinkedHashSet} with an initial capacity that accommodates |
| * an expected number of elements, use {@link #newLinkedHashSet(int) newLinkedHashSet}. |
| * |
| * @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). |
| * |
| * @apiNote |
| * To create a {@code LinkedHashSet} with an initial capacity that accommodates |
| * an expected number of elements, use {@link #newLinkedHashSet(int) newLinkedHashSet}. |
| * |
| * @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(HashMap.calculateHashMapCapacity(Math.max(c.size(), 12)), .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); |
| } |
| |
| /** |
| * Creates a new, empty LinkedHashSet suitable for the expected number of elements. |
| * The returned set uses the default load factor of 0.75, and its initial capacity is |
| * generally large enough so that the expected number of elements can be added |
| * without resizing the set. |
| * |
| * @param numElements the expected number of elements |
| * @param <T> the type of elements maintained by the new set |
| * @return the newly created set |
| * @throws IllegalArgumentException if numElements is negative |
| * @since 19 |
| */ |
| public static <T> LinkedHashSet<T> newLinkedHashSet(int numElements) { |
| if (numElements < 0) { |
| throw new IllegalArgumentException("Negative number of elements: " + numElements); |
| } |
| return new LinkedHashSet<>(HashMap.calculateHashMapCapacity(numElements)); |
| } |
| |
| @SuppressWarnings("unchecked") |
| LinkedHashMap<E, Object> map() { |
| return (LinkedHashMap<E, Object>) map; |
| } |
| |
| /** |
| * {@inheritDoc} |
| * <p> |
| * If this set already contains the element, it is relocated if necessary so that it is |
| * first in encounter order. |
| * |
| * @since 21 |
| */ |
| public void addFirst(E e) { |
| map().putFirst(e, PRESENT); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * <p> |
| * If this set already contains the element, it is relocated if necessary so that it is |
| * last in encounter order. |
| * |
| * @since 21 |
| */ |
| public void addLast(E e) { |
| map().putLast(e, PRESENT); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * @throws NoSuchElementException {@inheritDoc} |
| * @since 21 |
| */ |
| public E getFirst() { |
| return map().sequencedKeySet().getFirst(); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * @throws NoSuchElementException {@inheritDoc} |
| * @since 21 |
| */ |
| public E getLast() { |
| return map().sequencedKeySet().getLast(); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * @throws NoSuchElementException {@inheritDoc} |
| * @since 21 |
| */ |
| public E removeFirst() { |
| return map().sequencedKeySet().removeFirst(); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * @throws NoSuchElementException {@inheritDoc} |
| * @since 21 |
| */ |
| public E removeLast() { |
| return map().sequencedKeySet().removeLast(); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * <p> |
| * Modifications to the reversed view are permitted and will be propagated to this set. |
| * In addition, modifications to this set will be visible in the reversed view. |
| * |
| * @return {@inheritDoc} |
| * @since 21 |
| */ |
| public SequencedSet<E> reversed() { |
| class ReverseLinkedHashSetView extends AbstractSet<E> implements SequencedSet<E> { |
| public int size() { return LinkedHashSet.this.size(); } |
| public Iterator<E> iterator() { return map().sequencedKeySet().reversed().iterator(); } |
| public boolean add(E e) { return LinkedHashSet.this.add(e); } |
| public void addFirst(E e) { LinkedHashSet.this.addLast(e); } |
| public void addLast(E e) { LinkedHashSet.this.addFirst(e); } |
| public E getFirst() { return LinkedHashSet.this.getLast(); } |
| public E getLast() { return LinkedHashSet.this.getFirst(); } |
| public E removeFirst() { return LinkedHashSet.this.removeLast(); } |
| public E removeLast() { return LinkedHashSet.this.removeFirst(); } |
| public SequencedSet<E> reversed() { return LinkedHashSet.this; } |
| public Object[] toArray() { return map().keysToArray(new Object[map.size()], true); } |
| public <T> T[] toArray(T[] a) { return map().keysToArray(map.prepareArray(a), true); } |
| } |
| |
| return new ReverseLinkedHashSetView(); |
| } |
| } |
