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/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/*
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* This file is available under and governed by the GNU General Public
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* License version 2 only, as published by the Free Software Foundation.
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* However, the following notice accompanied the original version of this
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* file:
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*
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/licenses/publicdomain
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*/
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package java.util.concurrent;
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import java.util.*;
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import sun.misc.Unsafe;
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/**
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* A scalable concurrent {@link NavigableSet} implementation based on
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* a {@link ConcurrentSkipListMap}. The elements of the set are kept
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* sorted according to their {@linkplain Comparable natural ordering},
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* or by a {@link Comparator} provided at set creation time, depending
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* on which constructor is used.
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*
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* <p>This implementation provides expected average <i>log(n)</i> time
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* cost for the <tt>contains</tt>, <tt>add</tt>, and <tt>remove</tt>
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* operations and their variants. Insertion, removal, and access
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* operations safely execute concurrently by multiple threads.
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* Iterators are <i>weakly consistent</i>, returning elements
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* reflecting the state of the set at some point at or since the
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* creation of the iterator. They do <em>not</em> throw {@link
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* ConcurrentModificationException}, and may proceed concurrently with
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* other operations. Ascending ordered views and their iterators are
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* faster than descending ones.
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*
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* <p>Beware that, unlike in most collections, the <tt>size</tt>
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* method is <em>not</em> a constant-time operation. Because of the
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* asynchronous nature of these sets, determining the current number
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* of elements requires a traversal of the elements. Additionally, the
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* bulk operations <tt>addAll</tt>, <tt>removeAll</tt>,
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* <tt>retainAll</tt>, and <tt>containsAll</tt> are <em>not</em>
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* guaranteed to be performed atomically. For example, an iterator
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* operating concurrently with an <tt>addAll</tt> operation might view
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* only some of the added elements.
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*
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* <p>This class and its iterators implement all of the
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* <em>optional</em> methods of the {@link Set} and {@link Iterator}
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* interfaces. Like most other concurrent collection implementations,
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* this class does not permit the use of <tt>null</tt> elements,
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* because <tt>null</tt> arguments and return values cannot be reliably
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* distinguished from the absence of elements.
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*
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* <p>This class is a member of the
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* <a href="{@docRoot}/../technotes/guides/collections/index.html">
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* Java Collections Framework</a>.
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*
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* @author Doug Lea
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* @param <E> the type of elements maintained by this set
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* @since 1.6
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*/
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public class ConcurrentSkipListSet<E>
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extends AbstractSet<E>
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implements NavigableSet<E>, Cloneable, java.io.Serializable {
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private static final long serialVersionUID = -2479143111061671589L;
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/**
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* The underlying map. Uses Boolean.TRUE as value for each
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* element. This field is declared final for the sake of thread
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* safety, which entails some ugliness in clone()
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*/
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private final ConcurrentNavigableMap<E,Object> m;
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/**
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* Constructs a new, empty set that orders its elements according to
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* their {@linkplain Comparable natural ordering}.
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*/
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public ConcurrentSkipListSet() {
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m = new ConcurrentSkipListMap<E,Object>();
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}
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/**
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* Constructs a new, empty set that orders its elements according to
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* the specified comparator.
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*
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* @param comparator the comparator that will be used to order this set.
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* If <tt>null</tt>, the {@linkplain Comparable natural
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* ordering} of the elements will be used.
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*/
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public ConcurrentSkipListSet(Comparator<? super E> comparator) {
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m = new ConcurrentSkipListMap<E,Object>(comparator);
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}
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/**
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* Constructs a new set containing the elements in the specified
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* collection, that orders its elements according to their
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* {@linkplain Comparable natural ordering}.
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*
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* @param c The elements that will comprise the new set
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* @throws ClassCastException if the elements in <tt>c</tt> are
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* not {@link Comparable}, or are not mutually comparable
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* @throws NullPointerException if the specified collection or any
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* of its elements are null
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*/
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public ConcurrentSkipListSet(Collection<? extends E> c) {
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m = new ConcurrentSkipListMap<E,Object>();
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addAll(c);
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}
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/**
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* Constructs a new set containing the same elements and using the
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* same ordering as the specified sorted set.
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*
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* @param s sorted set whose elements will comprise the new set
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* @throws NullPointerException if the specified sorted set or any
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* of its elements are null
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*/
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public ConcurrentSkipListSet(SortedSet<E> s) {
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m = new ConcurrentSkipListMap<E,Object>(s.comparator());
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addAll(s);
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}
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/**
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* For use by submaps
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*/
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ConcurrentSkipListSet(ConcurrentNavigableMap<E,Object> m) {
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this.m = m;
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}
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/**
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* Returns a shallow copy of this <tt>ConcurrentSkipListSet</tt>
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* instance. (The elements themselves are not cloned.)
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*
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* @return a shallow copy of this set
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*/
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public ConcurrentSkipListSet<E> clone() {
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ConcurrentSkipListSet<E> clone = null;
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try {
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clone = (ConcurrentSkipListSet<E>) super.clone();
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clone.setMap(new ConcurrentSkipListMap(m));
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} catch (CloneNotSupportedException e) {
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throw new InternalError();
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}
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return clone;
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}
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/* ---------------- Set operations -------------- */
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/**
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* Returns the number of elements in this set. If this set
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* contains more than <tt>Integer.MAX_VALUE</tt> elements, it
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* returns <tt>Integer.MAX_VALUE</tt>.
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*
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* <p>Beware that, unlike in most collections, this method is
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* <em>NOT</em> a constant-time operation. Because of the
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* asynchronous nature of these sets, determining the current
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* number of elements requires traversing them all to count them.
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* Additionally, it is possible for the size to change during
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* execution of this method, in which case the returned result
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* will be inaccurate. Thus, this method is typically not very
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* useful in concurrent applications.
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*
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* @return the number of elements in this set
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*/
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public int size() {
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return m.size();
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}
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/**
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* Returns <tt>true</tt> if this set contains no elements.
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* @return <tt>true</tt> if this set contains no elements
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*/
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public boolean isEmpty() {
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return m.isEmpty();
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}
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/**
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* Returns <tt>true</tt> if this set contains the specified element.
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* More formally, returns <tt>true</tt> if and only if this set
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* contains an element <tt>e</tt> such that <tt>o.equals(e)</tt>.
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*
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* @param o object to be checked for containment in this set
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* @return <tt>true</tt> if this set contains the specified element
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* @throws ClassCastException if the specified element cannot be
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* compared with the elements currently in this set
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* @throws NullPointerException if the specified element is null
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*/
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public boolean contains(Object o) {
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return m.containsKey(o);
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}
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/**
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* Adds the specified element to this set if it is not already present.
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* More formally, adds the specified element <tt>e</tt> to this set if
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* the set contains no element <tt>e2</tt> such that <tt>e.equals(e2)</tt>.
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* If this set already contains the element, the call leaves the set
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* unchanged and returns <tt>false</tt>.
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*
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* @param e element to be added to this set
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* @return <tt>true</tt> if this set did not already contain the
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* specified element
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* @throws ClassCastException if <tt>e</tt> cannot be compared
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* with the elements currently in this set
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* @throws NullPointerException if the specified element is null
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*/
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public boolean add(E e) {
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return m.putIfAbsent(e, Boolean.TRUE) == null;
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}
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/**
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* Removes the specified element from this set if it is present.
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* More formally, removes an element <tt>e</tt> such that
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* <tt>o.equals(e)</tt>, if this set contains such an element.
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* Returns <tt>true</tt> if this set contained the element (or
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* equivalently, if this set changed as a result of the call).
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* (This set will not contain the element once the call returns.)
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*
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* @param o object to be removed from this set, if present
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* @return <tt>true</tt> if this set contained the specified element
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* @throws ClassCastException if <tt>o</tt> cannot be compared
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* with the elements currently in this set
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* @throws NullPointerException if the specified element is null
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*/
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public boolean remove(Object o) {
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return m.remove(o, Boolean.TRUE);
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}
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/**
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* Removes all of the elements from this set.
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*/
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public void clear() {
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m.clear();
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}
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/**
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* Returns an iterator over the elements in this set in ascending order.
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*
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* @return an iterator over the elements in this set in ascending order
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*/
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public Iterator<E> iterator() {
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return m.navigableKeySet().iterator();
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}
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/**
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* Returns an iterator over the elements in this set in descending order.
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*
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* @return an iterator over the elements in this set in descending order
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*/
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public Iterator<E> descendingIterator() {
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return m.descendingKeySet().iterator();
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}
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/* ---------------- AbstractSet Overrides -------------- */
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/**
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* Compares the specified object with this set for equality. Returns
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* <tt>true</tt> if the specified object is also a set, the two sets
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* have the same size, and every member of the specified set is
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* contained in this set (or equivalently, every member of this set is
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* contained in the specified set). This definition ensures that the
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* equals method works properly across different implementations of the
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* set interface.
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*
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* @param o the object to be compared for equality with this set
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* @return <tt>true</tt> if the specified object is equal to this set
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*/
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public boolean equals(Object o) {
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// Override AbstractSet version to avoid calling size()
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if (o == this)
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return true;
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if (!(o instanceof Set))
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return false;
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Collection<?> c = (Collection<?>) o;
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try {
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return containsAll(c) && c.containsAll(this);
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} catch (ClassCastException unused) {
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return false;
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} catch (NullPointerException unused) {
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return false;
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}
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}
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/**
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* Removes from this set all of its elements that are contained in
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* the specified collection. If the specified collection is also
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* a set, this operation effectively modifies this set so that its
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* value is the <i>asymmetric set difference</i> of the two sets.
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*
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* @param c collection containing elements to be removed from this set
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* @return <tt>true</tt> if this set changed as a result of the call
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* @throws ClassCastException if the types of one or more elements in this
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* set are incompatible with the specified collection
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* @throws NullPointerException if the specified collection or any
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* of its elements are null
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*/
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public boolean removeAll(Collection<?> c) {
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// Override AbstractSet version to avoid unnecessary call to size()
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boolean modified = false;
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for (Iterator<?> i = c.iterator(); i.hasNext(); )
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if (remove(i.next()))
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modified = true;
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return modified;
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}
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329 |
/* ---------------- Relational operations -------------- */
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/**
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* @throws ClassCastException {@inheritDoc}
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* @throws NullPointerException if the specified element is null
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*/
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public E lower(E e) {
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return m.lowerKey(e);
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}
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339 |
/**
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* @throws ClassCastException {@inheritDoc}
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341 |
* @throws NullPointerException if the specified element is null
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*/
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public E floor(E e) {
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return m.floorKey(e);
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}
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346 |
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347 |
/**
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348 |
* @throws ClassCastException {@inheritDoc}
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349 |
* @throws NullPointerException if the specified element is null
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350 |
*/
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public E ceiling(E e) {
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return m.ceilingKey(e);
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}
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354 |
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355 |
/**
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356 |
* @throws ClassCastException {@inheritDoc}
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|
357 |
* @throws NullPointerException if the specified element is null
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358 |
*/
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public E higher(E e) {
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return m.higherKey(e);
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}
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363 |
public E pollFirst() {
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Map.Entry<E,Object> e = m.pollFirstEntry();
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return (e == null) ? null : e.getKey();
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}
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368 |
public E pollLast() {
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Map.Entry<E,Object> e = m.pollLastEntry();
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return (e == null) ? null : e.getKey();
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}
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373 |
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374 |
/* ---------------- SortedSet operations -------------- */
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375 |
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376 |
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|
377 |
public Comparator<? super E> comparator() {
|
|
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return m.comparator();
|
|
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}
|
|
380 |
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|
381 |
/**
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|
382 |
* @throws NoSuchElementException {@inheritDoc}
|
|
383 |
*/
|
|
384 |
public E first() {
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|
385 |
return m.firstKey();
|
|
386 |
}
|
|
387 |
|
|
388 |
/**
|
|
389 |
* @throws NoSuchElementException {@inheritDoc}
|
|
390 |
*/
|
|
391 |
public E last() {
|
|
392 |
return m.lastKey();
|
|
393 |
}
|
|
394 |
|
|
395 |
/**
|
|
396 |
* @throws ClassCastException {@inheritDoc}
|
|
397 |
* @throws NullPointerException if {@code fromElement} or
|
|
398 |
* {@code toElement} is null
|
|
399 |
* @throws IllegalArgumentException {@inheritDoc}
|
|
400 |
*/
|
|
401 |
public NavigableSet<E> subSet(E fromElement,
|
|
402 |
boolean fromInclusive,
|
|
403 |
E toElement,
|
|
404 |
boolean toInclusive) {
|
|
405 |
return new ConcurrentSkipListSet<E>
|
|
406 |
(m.subMap(fromElement, fromInclusive,
|
|
407 |
toElement, toInclusive));
|
|
408 |
}
|
|
409 |
|
|
410 |
/**
|
|
411 |
* @throws ClassCastException {@inheritDoc}
|
|
412 |
* @throws NullPointerException if {@code toElement} is null
|
|
413 |
* @throws IllegalArgumentException {@inheritDoc}
|
|
414 |
*/
|
|
415 |
public NavigableSet<E> headSet(E toElement, boolean inclusive) {
|
|
416 |
return new ConcurrentSkipListSet<E>(m.headMap(toElement, inclusive));
|
|
417 |
}
|
|
418 |
|
|
419 |
/**
|
|
420 |
* @throws ClassCastException {@inheritDoc}
|
|
421 |
* @throws NullPointerException if {@code fromElement} is null
|
|
422 |
* @throws IllegalArgumentException {@inheritDoc}
|
|
423 |
*/
|
|
424 |
public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
|
|
425 |
return new ConcurrentSkipListSet<E>(m.tailMap(fromElement, inclusive));
|
|
426 |
}
|
|
427 |
|
|
428 |
/**
|
|
429 |
* @throws ClassCastException {@inheritDoc}
|
|
430 |
* @throws NullPointerException if {@code fromElement} or
|
|
431 |
* {@code toElement} is null
|
|
432 |
* @throws IllegalArgumentException {@inheritDoc}
|
|
433 |
*/
|
|
434 |
public NavigableSet<E> subSet(E fromElement, E toElement) {
|
|
435 |
return subSet(fromElement, true, toElement, false);
|
|
436 |
}
|
|
437 |
|
|
438 |
/**
|
|
439 |
* @throws ClassCastException {@inheritDoc}
|
|
440 |
* @throws NullPointerException if {@code toElement} is null
|
|
441 |
* @throws IllegalArgumentException {@inheritDoc}
|
|
442 |
*/
|
|
443 |
public NavigableSet<E> headSet(E toElement) {
|
|
444 |
return headSet(toElement, false);
|
|
445 |
}
|
|
446 |
|
|
447 |
/**
|
|
448 |
* @throws ClassCastException {@inheritDoc}
|
|
449 |
* @throws NullPointerException if {@code fromElement} is null
|
|
450 |
* @throws IllegalArgumentException {@inheritDoc}
|
|
451 |
*/
|
|
452 |
public NavigableSet<E> tailSet(E fromElement) {
|
|
453 |
return tailSet(fromElement, true);
|
|
454 |
}
|
|
455 |
|
|
456 |
/**
|
|
457 |
* Returns a reverse order view of the elements contained in this set.
|
|
458 |
* The descending set is backed by this set, so changes to the set are
|
|
459 |
* reflected in the descending set, and vice-versa.
|
|
460 |
*
|
|
461 |
* <p>The returned set has an ordering equivalent to
|
|
462 |
* <tt>{@link Collections#reverseOrder(Comparator) Collections.reverseOrder}(comparator())</tt>.
|
|
463 |
* The expression {@code s.descendingSet().descendingSet()} returns a
|
|
464 |
* view of {@code s} essentially equivalent to {@code s}.
|
|
465 |
*
|
|
466 |
* @return a reverse order view of this set
|
|
467 |
*/
|
|
468 |
public NavigableSet<E> descendingSet() {
|
|
469 |
return new ConcurrentSkipListSet(m.descendingMap());
|
|
470 |
}
|
|
471 |
|
|
472 |
// Support for resetting map in clone
|
|
473 |
private static final Unsafe unsafe = Unsafe.getUnsafe();
|
|
474 |
private static final long mapOffset;
|
|
475 |
static {
|
|
476 |
try {
|
|
477 |
mapOffset = unsafe.objectFieldOffset
|
|
478 |
(ConcurrentSkipListSet.class.getDeclaredField("m"));
|
|
479 |
} catch (Exception ex) { throw new Error(ex); }
|
|
480 |
}
|
|
481 |
private void setMap(ConcurrentNavigableMap<E,Object> map) {
|
|
482 |
unsafe.putObjectVolatile(this, mapOffset, map);
|
|
483 |
}
|
|
484 |
|
|
485 |
}
|