001/*
002 * Copyright 2011-2022 Ping Identity Corporation
003 * All Rights Reserved.
004 */
005/*
006 * Copyright 2011-2022 Ping Identity Corporation
007 *
008 * Licensed under the Apache License, Version 2.0 (the "License");
009 * you may not use this file except in compliance with the License.
010 * You may obtain a copy of the License at
011 *
012 *    http://www.apache.org/licenses/LICENSE-2.0
013 *
014 * Unless required by applicable law or agreed to in writing, software
015 * distributed under the License is distributed on an "AS IS" BASIS,
016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
017 * See the License for the specific language governing permissions and
018 * limitations under the License.
019 */
020/*
021 * Copyright (C) 2011-2022 Ping Identity Corporation
022 *
023 * This program is free software; you can redistribute it and/or modify
024 * it under the terms of the GNU General Public License (GPLv2 only)
025 * or the terms of the GNU Lesser General Public License (LGPLv2.1 only)
026 * as published by the Free Software Foundation.
027 *
028 * This program is distributed in the hope that it will be useful,
029 * but WITHOUT ANY WARRANTY; without even the implied warranty of
030 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
031 * GNU General Public License for more details.
032 *
033 * You should have received a copy of the GNU General Public License
034 * along with this program; if not, see <http://www.gnu.org/licenses>.
035 */
036package com.unboundid.util;
037
038
039
040import java.lang.ref.WeakReference;
041import java.util.Collection;
042import java.util.Iterator;
043import java.util.Map;
044import java.util.Set;
045import java.util.WeakHashMap;
046
047
048
049/**
050 * This class provides a weak hash set, which maintains weak references to the
051 * elements it contains, so that they will be removed automatically once there
052 * are no more normal references to them.
053 * <BR><BR>
054 * Note that because this set uses weak references, elements may disappear from
055 * the set at any time without being explicitly removed.  This means that care
056 * must be taken to ensure that the result of one method must not be considered
057 * authoritative for subsequent calls to the same method or other methods in
058 * this class.
059 *
060 * @param  <T>  The type of element held in this set.
061 */
062@Mutable()
063@ThreadSafety(level=ThreadSafetyLevel.NOT_THREADSAFE)
064public final class WeakHashSet<T>
065       implements Set<T>
066{
067  // The map that will be used to provide the set implementation.
068  @NotNull private final WeakHashMap<T,WeakReference<T>> m;
069
070
071
072  /**
073   * Creates a new weak hash set with the default initial capacity.
074   */
075  public WeakHashSet()
076  {
077    m = new WeakHashMap<>(16);
078  }
079
080
081
082  /**
083   * Creates a new weak hash set with the specified initial capacity.
084   *
085   * @param  initialCapacity  The initial capacity for this weak hash set.  It
086   *                          must not be {@code null}.
087   */
088  public WeakHashSet(final int initialCapacity)
089  {
090    m = new WeakHashMap<>(initialCapacity);
091  }
092
093
094
095  /**
096   * Clears the contents of this set.
097   */
098  @Override()
099  public void clear()
100  {
101    m.clear();
102  }
103
104
105
106  /**
107   * Indicates whether this set is currently empty.
108   *
109   * @return  {@code true} if this set is empty, or {@code false} if not.
110   */
111  @Override()
112  public boolean isEmpty()
113  {
114    return m.isEmpty();
115  }
116
117
118
119  /**
120   * Retrieves the number of elements currently held in this set.
121   *
122   * @return  The number of elements currently held in this set.
123   */
124  @Override()
125  public int size()
126  {
127    return m.size();
128  }
129
130
131
132  /**
133   * Indicates whether this set contains the specified element.
134   *
135   * @param  e  The element for which to make the determination.
136   *
137   * @return  {@code true} if this set contains the specified element, or
138   *          {@code false} if not.
139   */
140  @Override()
141  public boolean contains(@NotNull final Object e)
142  {
143    return m.containsKey(e);
144  }
145
146
147
148  /**
149   * Indicates whether this set currently contains all of the elements in the
150   * provided collection.
151   *
152   * @param  c  The collection for which to make the determination.
153   *
154   * @return  {@code true} if this set currently contains all of the elements in
155   *          the provided collection, or {@code false} if not.
156   */
157  @Override()
158  public boolean containsAll(@NotNull final Collection<?> c)
159  {
160    return m.keySet().containsAll(c);
161  }
162
163
164
165  /**
166   * Retrieves the existing instance of the provided element from this set.
167   *
168   * @param  e  The object for which to obtain the existing element.
169   *
170   * @return  The existing instance of the provided element, or {@code null} if
171   *          the provided element is not contained in this set.
172   */
173  @Nullable()
174  public T get(@NotNull final T e)
175  {
176    final WeakReference<T> r = m.get(e);
177    if (r == null)
178    {
179      return null;
180    }
181    else
182    {
183      return r.get();
184    }
185  }
186
187
188
189  /**
190   * Adds the provided element to this set, if it does not already exist.
191   *
192   * @param  e  The element to be added to the set if it does not already exist.
193   *
194   * @return  {@code true} if the element was added to the set (because it was
195   *          not already present), or {@code false} if the element was not
196   *          added (because it was already in the set).
197   */
198  @Override()
199  public boolean add(@NotNull final T e)
200  {
201    if (m.containsKey(e))
202    {
203      return false;
204    }
205    else
206    {
207      m.put(e, new WeakReference<>(e));
208      return true;
209    }
210  }
211
212
213
214  /**
215   * Adds any elements from the provided collection to this set if they were
216   * not already present.
217   *
218   * @param  c  The collection containing elements to add.
219   *
220   * @return  {@code true} if at least one of the elements was not already in
221   *          the set and was added, or {@code false} if no elements were added
222   *          because they were already all present.
223   */
224  @Override()
225  public boolean addAll(@NotNull final Collection<? extends T> c)
226  {
227    boolean changed = false;
228    for (final T e : c)
229    {
230      if (! m.containsKey(e))
231      {
232        m.put(e, new WeakReference<>(e));
233        changed = true;
234      }
235    }
236
237    return changed;
238  }
239
240
241
242  /**
243   * Adds the provided element to the set if it does not already exist, and
244   * retrieves the value stored in the set.
245   *
246   * @param  e  The element to be added to the set if it does not already exist.
247   *
248   * @return  An existing version of the provided element if it was already in
249   *          the set, or the provided object if it was just added.
250   */
251  @Nullable()
252  public T addAndGet(@NotNull final T e)
253  {
254    final WeakReference<T> r = m.get(e);
255    if (r != null)
256    {
257      final T existingElement = r.get();
258      if (existingElement != null)
259      {
260        return existingElement;
261      }
262    }
263
264    m.put(e, new WeakReference<>(e));
265    return e;
266  }
267
268
269
270  /**
271   * Removes the specified element from this set, if it exists.
272   *
273   * @param  e  The element to be removed from this set.
274   *
275   * @return  {@code true} if the element existed in the set and was removed, or
276   *          {@code false} if not.
277   */
278  @Override()
279  public boolean remove(@NotNull final Object e)
280  {
281    return (m.remove(e) != null);
282  }
283
284
285
286  /**
287   * Removes all of the elements of the provided collection from this set.
288   *
289   * @param  c  The collection containing the elements to remove from this set.
290   *
291   * @return  {@code true} if at least one of the elements from the provided
292   *          collection were contained in and therefore removed from the set,
293   *          or {@code false} if none of the elements in the given collection
294   *          were contained in this set.
295   */
296  @Override()
297  public boolean removeAll(@NotNull final Collection<?> c)
298  {
299    boolean changed = false;
300    for (final Object o : c)
301    {
302      final Object e = m.remove(o);
303      if (e != null)
304      {
305        changed = true;
306      }
307    }
308
309    return changed;
310  }
311
312
313
314  /**
315   * Removes all elements from this set which are not contained in the provided
316   * collection.
317   *
318   * @param  c  The collection of elements to be retained.
319   *
320   * @return  {@code true} if this set contained at least one element not in the
321   *          provided collection that was therefore removed, or {@code false}
322   *          if this set did not have any elements that were not in the
323   *          provided collection.
324   */
325  @Override()
326  public boolean retainAll(@NotNull final Collection<?> c)
327  {
328    boolean changed = false;
329    final Iterator<Map.Entry<T,WeakReference<T>>> iterator =
330         m.entrySet().iterator();
331    while (iterator.hasNext())
332    {
333      final Map.Entry<T,WeakReference<T>> e = iterator.next();
334      if (! c.contains(e.getKey()))
335      {
336        iterator.remove();
337        changed = true;
338      }
339    }
340
341    return changed;
342  }
343
344
345
346  /**
347   * Retrieves an iterator across all elements in this set.
348   *
349   * @return  An iterator across all elements in this set.
350   */
351  @Override()
352  @NotNull()
353  public Iterator<T> iterator()
354  {
355    return m.keySet().iterator();
356  }
357
358
359
360  /**
361   * Retrieves an array containing all of the elements currently held in this
362   * set.
363   *
364   * @return  An array containing all of the elements currently held in this
365   *          set.
366   */
367  @Override()
368  @NotNull()
369  public Object[] toArray()
370  {
371    return m.keySet().toArray();
372  }
373
374
375
376  /**
377   * Retrieves an array containing all of the elements currently held in this
378   * set.
379   *
380   * @param  a  An array into which the elements will be added if there is
381   *            sufficient space.
382   *
383   * @param  <E>  The type of element for the given array.
384   *
385   * @return  The provided array (with the first {@code null} element depicting
386   *          the end of the set elements if the given array is larger than this
387   *          set), or a newly-allocated array if the provided array was not
388   *          large enough.
389   */
390  @Override()
391  @NotNull()
392  public <E> E[] toArray(@NotNull final E[] a)
393  {
394    return m.keySet().toArray(a);
395  }
396
397
398
399  /**
400   * Retrieves a hash code for this set.
401   *
402   * @return  A hash code for this set.
403   */
404  @Override()
405  public int hashCode()
406  {
407    return m.keySet().hashCode();
408  }
409
410
411
412  /**
413   * Indicates whether the provided object is equal to this set.
414   *
415   * @param  o  The object for which to make the determination.
416   *
417   * @return  {@code true} if the provided object is a non-{@code null} set with
418   *          the same elements as this set, or {@code false} if not.
419   */
420  @Override()
421  public boolean equals(@Nullable final Object o)
422  {
423    return ((o != null) && (o instanceof Set) && m.keySet().equals(o));
424  }
425
426
427
428  /**
429   * Retrieves a string representation of this set.
430   *
431   * @return  A string representation of this set.
432   */
433  @Override()
434  @NotNull()
435  public String toString()
436  {
437    return m.keySet().toString();
438  }
439}