1 /*
2 * Copyright (c) 1998, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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23 * questions.
24 */
25
26 package java.util;
27
28 /**
29 * A {@link NavigableSet} implementation based on a {@link TreeMap}.
30 * The elements are ordered using their {@linkplain Comparable natural
31 * ordering}, or by a {@link Comparator} provided at set creation
32 * time, depending on which constructor is used.
33 *
34 * <p>This implementation provides guaranteed log(n) time cost for the basic
35 * operations ({@code add}, {@code remove} and {@code contains}).
36 *
37 * <p>Note that the ordering maintained by a set (whether or not an explicit
38 * comparator is provided) must be <i>consistent with equals</i> if it is to
39 * correctly implement the {@code Set} interface. (See {@code Comparable}
40 * or {@code Comparator} for a precise definition of <i>consistent with
41 * equals</i>.) This is so because the {@code Set} interface is defined in
42 * terms of the {@code equals} operation, but a {@code TreeSet} instance
43 * performs all element comparisons using its {@code compareTo} (or
44 * {@code compare}) method, so two elements that are deemed equal by this method
45 * are, from the standpoint of the set, equal. The behavior of a set
46 * <i>is</i> well-defined even if its ordering is inconsistent with equals; it
47 * just fails to obey the general contract of the {@code Set} interface.
48 *
49 * <p><strong>Note that this implementation is not synchronized.</strong>
50 * If multiple threads access a tree set concurrently, and at least one
51 * of the threads modifies the set, it <i>must</i> be synchronized
52 * externally. This is typically accomplished by synchronizing on some
53 * object that naturally encapsulates the set.
54 * If no such object exists, the set should be "wrapped" using the
55 * {@link Collections#synchronizedSortedSet Collections.synchronizedSortedSet}
56 * method. This is best done at creation time, to prevent accidental
57 * unsynchronized access to the set: <pre>
58 * SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));</pre>
59 *
60 * <p>The iterators returned by this class's {@code iterator} method are
61 * <i>fail-fast</i>: if the set is modified at any time after the iterator is
62 * created, in any way except through the iterator's own {@code remove}
63 * method, the iterator will throw a {@link ConcurrentModificationException}.
64 * Thus, in the face of concurrent modification, the iterator fails quickly
65 * and cleanly, rather than risking arbitrary, non-deterministic behavior at
66 * an undetermined time in the future.
67 *
68 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
69 * as it is, generally speaking, impossible to make any hard guarantees in the
70 * presence of unsynchronized concurrent modification. Fail-fast iterators
71 * throw {@code ConcurrentModificationException} on a best-effort basis.
72 * Therefore, it would be wrong to write a program that depended on this
73 * exception for its correctness: <i>the fail-fast behavior of iterators
74 * should be used only to detect bugs.</i>
75 *
76 * <p>This class is a member of the
77 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
78 * Java Collections Framework</a>.
79 *
80 * @param <E> the type of elements maintained by this set
81 *
82 * @author Josh Bloch
83 * @see Collection
84 * @see Set
85 * @see HashSet
86 * @see Comparable
87 * @see Comparator
88 * @see TreeMap
89 * @since 1.2
90 */
91
92 public class TreeSet<E> extends AbstractSet<E>
93 implements NavigableSet<E>, Cloneable, java.io.Serializable
94 {
95 /**
96 * The backing map.
97 */
98 private transient NavigableMap<E,Object> m;
99
100 // Dummy value to associate with an Object in the backing Map
101 private static final Object PRESENT = new Object();
102
103 /**
104 * Constructs a set backed by the specified navigable map.
105 */
106 TreeSet(NavigableMap<E,Object> m) {
107 this.m = m;
108 }
109
110 /**
111 * Constructs a new, empty tree set, sorted according to the
112 * natural ordering of its elements. All elements inserted into
113 * the set must implement the {@link Comparable} interface.
114 * Furthermore, all such elements must be <i>mutually
115 * comparable</i>: {@code e1.compareTo(e2)} must not throw a
116 * {@code ClassCastException} for any elements {@code e1} and
117 * {@code e2} in the set. If the user attempts to add an element
118 * to the set that violates this constraint (for example, the user
119 * attempts to add a string element to a set whose elements are
120 * integers), the {@code add} call will throw a
121 * {@code ClassCastException}.
122 */
123 public TreeSet() {
124 this(new TreeMap<>());
125 }
126
127 /**
128 * Constructs a new, empty tree set, sorted according to the specified
129 * comparator. All elements inserted into the set must be <i>mutually
130 * comparable</i> by the specified comparator: {@code comparator.compare(e1,
131 * e2)} must not throw a {@code ClassCastException} for any elements
132 * {@code e1} and {@code e2} in the set. If the user attempts to add
133 * an element to the set that violates this constraint, the
134 * {@code add} call will throw a {@code ClassCastException}.
135 *
136 * @param comparator the comparator that will be used to order this set.
137 * If {@code null}, the {@linkplain Comparable natural
138 * ordering} of the elements will be used.
139 */
140 public TreeSet(Comparator<? super E> comparator) {
141 this(new TreeMap<>(comparator));
142 }
143
144 /**
145 * Constructs a new tree set containing the elements in the specified
146 * collection, sorted according to the <i>natural ordering</i> of its
147 * elements. All elements inserted into the set must implement the
148 * {@link Comparable} interface. Furthermore, all such elements must be
149 * <i>mutually comparable</i>: {@code e1.compareTo(e2)} must not throw a
150 * {@code ClassCastException} for any elements {@code e1} and
151 * {@code e2} in the set.
152 *
153 * @param c collection whose elements will comprise the new set
154 * @throws ClassCastException if the elements in {@code c} are
155 * not {@link Comparable}, or are not mutually comparable
156 * @throws NullPointerException if the specified collection is null
157 */
158 public TreeSet(Collection<? extends E> c) {
159 this();
160 addAll(c);
161 }
162
163 /**
164 * Constructs a new tree set containing the same elements and
165 * using the same ordering as the specified sorted set.
166 *
167 * @param s sorted set whose elements will comprise the new set
168 * @throws NullPointerException if the specified sorted set is null
169 */
170 public TreeSet(SortedSet<E> s) {
171 this(s.comparator());
172 addAll(s);
173 }
174
175 /**
176 * Returns an iterator over the elements in this set in ascending order.
177 *
178 * @return an iterator over the elements in this set in ascending order
179 */
180 public Iterator<E> iterator() {
181 return m.navigableKeySet().iterator();
182 }
183
184 /**
185 * Returns an iterator over the elements in this set in descending order.
186 *
187 * @return an iterator over the elements in this set in descending order
188 * @since 1.6
189 */
190 public Iterator<E> descendingIterator() {
191 return m.descendingKeySet().iterator();
192 }
193
194 /**
195 * @since 1.6
196 */
197 public NavigableSet<E> descendingSet() {
198 return new TreeSet<>(m.descendingMap());
199 }
200
201 /**
202 * Returns the number of elements in this set (its cardinality).
203 *
204 * @return the number of elements in this set (its cardinality)
205 */
206 public int size() {
207 return m.size();
208 }
209
210 /**
211 * Returns {@code true} if this set contains no elements.
212 *
213 * @return {@code true} if this set contains no elements
214 */
215 public boolean isEmpty() {
216 return m.isEmpty();
217 }
218
219 /**
220 * Returns {@code true} if this set contains the specified element.
221 * More formally, returns {@code true} if and only if this set
222 * contains an element {@code e} such that
223 * {@code Objects.equals(o, e)}.
224 *
225 * @param o object to be checked for containment in this set
226 * @return {@code true} if this set contains the specified element
227 * @throws ClassCastException if the specified object cannot be compared
228 * with the elements currently in the set
229 * @throws NullPointerException if the specified element is null
230 * and this set uses natural ordering, or its comparator
231 * does not permit null elements
232 */
233 public boolean contains(Object o) {
234 return m.containsKey(o);
235 }
236
237 /**
238 * Adds the specified element to this set if it is not already present.
239 * More formally, adds the specified element {@code e} to this set if
240 * the set contains no element {@code e2} such that
241 * {@code Objects.equals(e, e2)}.
242 * If this set already contains the element, the call leaves the set
243 * unchanged and returns {@code false}.
244 *
245 * @param e element to be added to this set
246 * @return {@code true} if this set did not already contain the specified
247 * element
248 * @throws ClassCastException if the specified object cannot be compared
249 * with the elements currently in this set
250 * @throws NullPointerException if the specified element is null
251 * and this set uses natural ordering, or its comparator
252 * does not permit null elements
253 */
254 public boolean add(E e) {
255 return m.put(e, PRESENT)==null;
256 }
257
258 /**
259 * Removes the specified element from this set if it is present.
260 * More formally, removes an element {@code e} such that
261 * {@code Objects.equals(o, e)},
262 * if this set contains such an element. Returns {@code true} if
263 * this set contained the element (or equivalently, if this set
264 * changed as a result of the call). (This set will not contain the
265 * element once the call returns.)
266 *
267 * @param o object to be removed from this set, if present
268 * @return {@code true} if this set contained the specified element
269 * @throws ClassCastException if the specified object cannot be compared
270 * with the elements currently in this set
271 * @throws NullPointerException if the specified element is null
272 * and this set uses natural ordering, or its comparator
273 * does not permit null elements
274 */
275 public boolean remove(Object o) {
276 return m.remove(o)==PRESENT;
277 }
278
279 /**
280 * Removes all of the elements from this set.
281 * The set will be empty after this call returns.
282 */
283 public void clear() {
284 m.clear();
285 }
286
287 /**
288 * Adds all of the elements in the specified collection to this set.
289 *
290 * @param c collection containing elements to be added to this set
291 * @return {@code true} if this set changed as a result of the call
292 * @throws ClassCastException if the elements provided cannot be compared
293 * with the elements currently in the set
294 * @throws NullPointerException if the specified collection is null or
295 * if any element is null and this set uses natural ordering, or
296 * its comparator does not permit null elements
297 */
298 public boolean addAll(Collection<? extends E> c) {
299 // Use linear-time version if applicable
300 if (m.size()==0 && c.size() > 0 &&
301 c instanceof SortedSet &&
302 m instanceof TreeMap) {
303 SortedSet<? extends E> set = (SortedSet<? extends E>) c;
304 TreeMap<E,Object> map = (TreeMap<E, Object>) m;
305 Comparator<?> cc = set.comparator();
306 Comparator<? super E> mc = map.comparator();
307 if (cc==mc || (cc != null && cc.equals(mc))) {
308 map.addAllForTreeSet(set, PRESENT);
309 return true;
310 }
311 }
312 return super.addAll(c);
313 }
314
315 /**
316 * @throws ClassCastException {@inheritDoc}
317 * @throws NullPointerException if {@code fromElement} or {@code toElement}
318 * is null and this set uses natural ordering, or its comparator
319 * does not permit null elements
320 * @throws IllegalArgumentException {@inheritDoc}
321 * @since 1.6
322 */
323 public NavigableSet<E> subSet(E fromElement, boolean fromInclusive,
324 E toElement, boolean toInclusive) {
325 return new TreeSet<>(m.subMap(fromElement, fromInclusive,
326 toElement, toInclusive));
327 }
328
329 /**
330 * @throws ClassCastException {@inheritDoc}
331 * @throws NullPointerException if {@code toElement} is null and
332 * this set uses natural ordering, or its comparator does
333 * not permit null elements
334 * @throws IllegalArgumentException {@inheritDoc}
335 * @since 1.6
336 */
337 public NavigableSet<E> headSet(E toElement, boolean inclusive) {
338 return new TreeSet<>(m.headMap(toElement, inclusive));
339 }
340
341 /**
342 * @throws ClassCastException {@inheritDoc}
343 * @throws NullPointerException if {@code fromElement} is null and
344 * this set uses natural ordering, or its comparator does
345 * not permit null elements
346 * @throws IllegalArgumentException {@inheritDoc}
347 * @since 1.6
348 */
349 public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
350 return new TreeSet<>(m.tailMap(fromElement, inclusive));
351 }
352
353 /**
354 * @throws ClassCastException {@inheritDoc}
355 * @throws NullPointerException if {@code fromElement} or
356 * {@code toElement} is null and this set uses natural ordering,
357 * or its comparator does not permit null elements
358 * @throws IllegalArgumentException {@inheritDoc}
359 */
360 public SortedSet<E> subSet(E fromElement, E toElement) {
361 return subSet(fromElement, true, toElement, false);
362 }
363
364 /**
365 * @throws ClassCastException {@inheritDoc}
366 * @throws NullPointerException if {@code toElement} is null
367 * and this set uses natural ordering, or its comparator does
368 * not permit null elements
369 * @throws IllegalArgumentException {@inheritDoc}
370 */
371 public SortedSet<E> headSet(E toElement) {
372 return headSet(toElement, false);
373 }
374
375 /**
376 * @throws ClassCastException {@inheritDoc}
377 * @throws NullPointerException if {@code fromElement} is null
378 * and this set uses natural ordering, or its comparator does
379 * not permit null elements
380 * @throws IllegalArgumentException {@inheritDoc}
381 */
382 public SortedSet<E> tailSet(E fromElement) {
383 return tailSet(fromElement, true);
384 }
385
386 public Comparator<? super E> comparator() {
387 return m.comparator();
388 }
389
390 /**
391 * @throws NoSuchElementException {@inheritDoc}
392 */
393 public E first() {
394 return m.firstKey();
395 }
396
397 /**
398 * @throws NoSuchElementException {@inheritDoc}
399 */
400 public E last() {
401 return m.lastKey();
402 }
403
404 // NavigableSet API methods
405
406 /**
407 * @throws ClassCastException {@inheritDoc}
408 * @throws NullPointerException if the specified element is null
409 * and this set uses natural ordering, or its comparator
410 * does not permit null elements
411 * @since 1.6
412 */
413 public E lower(E e) {
414 return m.lowerKey(e);
415 }
416
417 /**
418 * @throws ClassCastException {@inheritDoc}
419 * @throws NullPointerException if the specified element is null
420 * and this set uses natural ordering, or its comparator
421 * does not permit null elements
422 * @since 1.6
423 */
424 public E floor(E e) {
425 return m.floorKey(e);
426 }
427
428 /**
429 * @throws ClassCastException {@inheritDoc}
430 * @throws NullPointerException if the specified element is null
431 * and this set uses natural ordering, or its comparator
432 * does not permit null elements
433 * @since 1.6
434 */
435 public E ceiling(E e) {
436 return m.ceilingKey(e);
437 }
438
439 /**
440 * @throws ClassCastException {@inheritDoc}
441 * @throws NullPointerException if the specified element is null
442 * and this set uses natural ordering, or its comparator
443 * does not permit null elements
444 * @since 1.6
445 */
446 public E higher(E e) {
447 return m.higherKey(e);
448 }
449
450 /**
451 * @since 1.6
452 */
453 public E pollFirst() {
454 Map.Entry<E,?> e = m.pollFirstEntry();
455 return (e == null) ? null : e.getKey();
456 }
457
458 /**
459 * @since 1.6
460 */
461 public E pollLast() {
462 Map.Entry<E,?> e = m.pollLastEntry();
463 return (e == null) ? null : e.getKey();
464 }
465
466 /**
467 * Returns a shallow copy of this {@code TreeSet} instance. (The elements
468 * themselves are not cloned.)
469 *
470 * @return a shallow copy of this set
471 */
472 @SuppressWarnings("unchecked")
473 public Object clone() {
474 TreeSet<E> clone;
475 try {
476 clone = (TreeSet<E>) super.clone();
477 } catch (CloneNotSupportedException e) {
478 throw new InternalError(e);
479 }
480
481 clone.m = new TreeMap<>(m);
482 return clone;
483 }
484
485 /**
486 * Save the state of the {@code TreeSet} instance to a stream (that is,
487 * serialize it).
488 *
489 * @serialData Emits the comparator used to order this set, or
490 * {@code null} if it obeys its elements' natural ordering
491 * (Object), followed by the size of the set (the number of
492 * elements it contains) (int), followed by all of its
493 * elements (each an Object) in order (as determined by the
494 * set's Comparator, or by the elements' natural ordering if
495 * the set has no Comparator).
496 */
497 private void writeObject(java.io.ObjectOutputStream s)
498 throws java.io.IOException {
499 // Write out any hidden stuff
500 s.defaultWriteObject();
501
502 // Write out Comparator
503 s.writeObject(m.comparator());
504
505 // Write out size
506 s.writeInt(m.size());
507
508 // Write out all elements in the proper order.
509 for (E e : m.keySet())
510 s.writeObject(e);
511 }
512
513 /**
514 * Reconstitute the {@code TreeSet} instance from a stream (that is,
515 * deserialize it).
516 */
517 private void readObject(java.io.ObjectInputStream s)
518 throws java.io.IOException, ClassNotFoundException {
519 // Read in any hidden stuff
520 s.defaultReadObject();
521
522 // Read in Comparator
523 @SuppressWarnings("unchecked")
524 Comparator<? super E> c = (Comparator<? super E>) s.readObject();
525
526 // Create backing TreeMap
527 TreeMap<E,Object> tm = new TreeMap<>(c);
528 m = tm;
529
530 // Read in size
531 int size = s.readInt();
532
533 tm.readTreeSet(size, s, PRESENT);
534 }
535
536 /**
537 * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
538 * and <em>fail-fast</em> {@link Spliterator} over the elements in this
539 * set.
540 *
541 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
542 * {@link Spliterator#DISTINCT}, {@link Spliterator#SORTED}, and
543 * {@link Spliterator#ORDERED}. Overriding implementations should document
544 * the reporting of additional characteristic values.
545 *
546 * <p>The spliterator's comparator (see
547 * {@link java.util.Spliterator#getComparator()}) is {@code null} if
548 * the tree set's comparator (see {@link #comparator()}) is {@code null}.
549 * Otherwise, the spliterator's comparator is the same as or imposes the
550 * same total ordering as the tree set's comparator.
551 *
552 * @return a {@code Spliterator} over the elements in this set
553 * @since 1.8
554 */
555 public Spliterator<E> spliterator() {
556 return TreeMap.keySpliteratorFor(m);
557 }
558
559 private static final long serialVersionUID = -2479143000061671589L;
560 }