001/*
002 * Copyright (C) 2008 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.collect;
018
019import static com.google.common.base.Preconditions.checkArgument;
020import static com.google.common.base.Preconditions.checkNotNull;
021
022import com.google.common.annotations.GwtCompatible;
023import com.google.common.annotations.GwtIncompatible;
024
025import java.io.InvalidObjectException;
026import java.io.ObjectInputStream;
027import java.io.Serializable;
028import java.util.ArrayList;
029import java.util.Arrays;
030import java.util.Collection;
031import java.util.Collections;
032import java.util.Comparator;
033import java.util.Iterator;
034import java.util.List;
035import java.util.NavigableSet;
036import java.util.SortedSet;
037
038import javax.annotation.Nullable;
039
040/**
041 * An immutable {@code SortedSet} that stores its elements in a sorted array.
042 * Some instances are ordered by an explicit comparator, while others follow the
043 * natural sort ordering of their elements. Either way, null elements are not
044 * supported.
045 *
046 * <p>Unlike {@link Collections#unmodifiableSortedSet}, which is a <i>view</i>
047 * of a separate collection that can still change, an instance of {@code
048 * ImmutableSortedSet} contains its own private data and will <i>never</i>
049 * change. This class is convenient for {@code public static final} sets
050 * ("constant sets") and also lets you easily make a "defensive copy" of a set
051 * provided to your class by a caller.
052 *
053 * <p>The sets returned by the {@link #headSet}, {@link #tailSet}, and
054 * {@link #subSet} methods share the same array as the original set, preventing
055 * that array from being garbage collected. If this is a concern, the data may
056 * be copied into a correctly-sized array by calling {@link #copyOfSorted}.
057 *
058 * <p><b>Note on element equivalence:</b> The {@link #contains(Object)},
059 * {@link #containsAll(Collection)}, and {@link #equals(Object)}
060 * implementations must check whether a provided object is equivalent to an
061 * element in the collection. Unlike most collections, an
062 * {@code ImmutableSortedSet} doesn't use {@link Object#equals} to determine if
063 * two elements are equivalent. Instead, with an explicit comparator, the
064 * following relation determines whether elements {@code x} and {@code y} are
065 * equivalent: <pre>   {@code
066 *
067 *   {(x, y) | comparator.compare(x, y) == 0}}</pre>
068 *
069 * With natural ordering of elements, the following relation determines whether
070 * two elements are equivalent: <pre>   {@code
071 *
072 *   {(x, y) | x.compareTo(y) == 0}}</pre>
073 *
074 * <b>Warning:</b> Like most sets, an {@code ImmutableSortedSet} will not
075 * function correctly if an element is modified after being placed in the set.
076 * For this reason, and to avoid general confusion, it is strongly recommended
077 * to place only immutable objects into this collection.
078 *
079 * <p><b>Note:</b> Although this class is not final, it cannot be subclassed as
080 * it has no public or protected constructors. Thus, instances of this type are
081 * guaranteed to be immutable.
082 *
083 * <p>See the Guava User Guide article on <a href=
084 * "http://code.google.com/p/guava-libraries/wiki/ImmutableCollectionsExplained">
085 * immutable collections</a>.
086 *
087 * @see ImmutableSet
088 * @author Jared Levy
089 * @author Louis Wasserman
090 * @since 2.0 (imported from Google Collections Library; implements {@code NavigableSet} since 12.0)
091 */
092// TODO(benyu): benchmark and optimize all creation paths, which are a mess now
093@GwtCompatible(serializable = true, emulated = true)
094@SuppressWarnings("serial") // we're overriding default serialization
095public abstract class ImmutableSortedSet<E> extends ImmutableSortedSetFauxverideShim<E>
096    implements NavigableSet<E>, SortedIterable<E> {
097
098  private static final Comparator<Comparable> NATURAL_ORDER =
099      Ordering.natural();
100
101  private static final ImmutableSortedSet<Comparable> NATURAL_EMPTY_SET =
102      new EmptyImmutableSortedSet<Comparable>(NATURAL_ORDER);
103
104  @SuppressWarnings("unchecked")
105  private static <E> ImmutableSortedSet<E> emptySet() {
106    return (ImmutableSortedSet<E>) NATURAL_EMPTY_SET;
107  }
108
109  static <E> ImmutableSortedSet<E> emptySet(
110      Comparator<? super E> comparator) {
111    if (NATURAL_ORDER.equals(comparator)) {
112      return emptySet();
113    } else {
114      return new EmptyImmutableSortedSet<E>(comparator);
115    }
116  }
117
118  /**
119   * Returns the empty immutable sorted set.
120   */
121  public static <E> ImmutableSortedSet<E> of() {
122    return emptySet();
123  }
124
125  /**
126   * Returns an immutable sorted set containing a single element.
127   */
128  public static <E extends Comparable<? super E>> ImmutableSortedSet<E> of(
129      E element) {
130    return new RegularImmutableSortedSet<E>(
131        ImmutableList.of(element), Ordering.natural());
132  }
133
134  /**
135   * Returns an immutable sorted set containing the given elements sorted by
136   * their natural ordering. When multiple elements are equivalent according to
137   * {@link Comparable#compareTo}, only the first one specified is included.
138   *
139   * @throws NullPointerException if any element is null
140   */
141  @SuppressWarnings("unchecked")
142  public static <E extends Comparable<? super E>> ImmutableSortedSet<E> of(
143      E e1, E e2) {
144    return copyOf(Ordering.natural(), Arrays.asList(e1, e2));
145  }
146
147  /**
148   * Returns an immutable sorted set containing the given elements sorted by
149   * their natural ordering. When multiple elements are equivalent according to
150   * {@link Comparable#compareTo}, only the first one specified is included.
151   *
152   * @throws NullPointerException if any element is null
153   */
154  @SuppressWarnings("unchecked")
155  public static <E extends Comparable<? super E>> ImmutableSortedSet<E> of(
156      E e1, E e2, E e3) {
157    return copyOf(Ordering.natural(), Arrays.asList(e1, e2, e3));
158  }
159
160  /**
161   * Returns an immutable sorted set containing the given elements sorted by
162   * their natural ordering. When multiple elements are equivalent according to
163   * {@link Comparable#compareTo}, only the first one specified is included.
164   *
165   * @throws NullPointerException if any element is null
166   */
167  @SuppressWarnings("unchecked")
168  public static <E extends Comparable<? super E>> ImmutableSortedSet<E> of(
169      E e1, E e2, E e3, E e4) {
170    return copyOf(Ordering.natural(), Arrays.asList(e1, e2, e3, e4));
171  }
172
173  /**
174   * Returns an immutable sorted set containing the given elements sorted by
175   * their natural ordering. When multiple elements are equivalent according to
176   * {@link Comparable#compareTo}, only the first one specified is included.
177   *
178   * @throws NullPointerException if any element is null
179   */
180  @SuppressWarnings("unchecked")
181  public static <E extends Comparable<? super E>> ImmutableSortedSet<E> of(
182      E e1, E e2, E e3, E e4, E e5) {
183    return copyOf(Ordering.natural(), Arrays.asList(e1, e2, e3, e4, e5));
184  }
185
186  /**
187   * Returns an immutable sorted set containing the given elements sorted by
188   * their natural ordering. When multiple elements are equivalent according to
189   * {@link Comparable#compareTo}, only the first one specified is included.
190   *
191   * @throws NullPointerException if any element is null
192   * @since 3.0 (source-compatible since 2.0)
193   */
194  @SuppressWarnings("unchecked")
195  public static <E extends Comparable<? super E>> ImmutableSortedSet<E> of(
196      E e1, E e2, E e3, E e4, E e5, E e6, E... remaining) {
197    int size = remaining.length + 6;
198    List<E> all = new ArrayList<E>(size);
199    Collections.addAll(all, e1, e2, e3, e4, e5, e6);
200    Collections.addAll(all, remaining);
201    return copyOf(Ordering.natural(), all);
202  }
203
204  // TODO(kevinb): Consider factory methods that reject duplicates
205
206  /**
207   * Returns an immutable sorted set containing the given elements sorted by
208   * their natural ordering. When multiple elements are equivalent according to
209   * {@link Comparable#compareTo}, only the first one specified is included.
210   *
211   * @throws NullPointerException if any of {@code elements} is null
212   * @since 3.0
213   */
214  public static <E extends Comparable<? super E>> ImmutableSortedSet<E> copyOf(
215      E[] elements) {
216    return copyOf(Ordering.natural(), Arrays.asList(elements));
217  }
218
219  /**
220   * Returns an immutable sorted set containing the given elements sorted by
221   * their natural ordering. When multiple elements are equivalent according to
222   * {@code compareTo()}, only the first one specified is included. To create a
223   * copy of a {@code SortedSet} that preserves the comparator, call {@link
224   * #copyOfSorted} instead. This method iterates over {@code elements} at most
225   * once.
226
227   *
228   * <p>Note that if {@code s} is a {@code Set<String>}, then {@code
229   * ImmutableSortedSet.copyOf(s)} returns an {@code ImmutableSortedSet<String>}
230   * containing each of the strings in {@code s}, while {@code
231   * ImmutableSortedSet.of(s)} returns an {@code
232   * ImmutableSortedSet<Set<String>>} containing one element (the given set
233   * itself).
234   *
235   * <p>Despite the method name, this method attempts to avoid actually copying
236   * the data when it is safe to do so. The exact circumstances under which a
237   * copy will or will not be performed are undocumented and subject to change.
238   *
239   * <p>This method is not type-safe, as it may be called on elements that are
240   * not mutually comparable.
241   *
242   * @throws ClassCastException if the elements are not mutually comparable
243   * @throws NullPointerException if any of {@code elements} is null
244   */
245  public static <E> ImmutableSortedSet<E> copyOf(
246      Iterable<? extends E> elements) {
247    // Hack around E not being a subtype of Comparable.
248    // Unsafe, see ImmutableSortedSetFauxverideShim.
249    @SuppressWarnings("unchecked")
250    Ordering<E> naturalOrder = (Ordering<E>) Ordering.<Comparable>natural();
251    return copyOf(naturalOrder, elements);
252  }
253
254  /**
255   * Returns an immutable sorted set containing the given elements sorted by
256   * their natural ordering. When multiple elements are equivalent according to
257   * {@code compareTo()}, only the first one specified is included. To create a
258   * copy of a {@code SortedSet} that preserves the comparator, call
259   * {@link #copyOfSorted} instead. This method iterates over {@code elements}
260   * at most once.
261   *
262   * <p>Note that if {@code s} is a {@code Set<String>}, then
263   * {@code ImmutableSortedSet.copyOf(s)} returns an
264   * {@code ImmutableSortedSet<String>} containing each of the strings in
265   * {@code s}, while {@code ImmutableSortedSet.of(s)} returns an
266   * {@code ImmutableSortedSet<Set<String>>} containing one element (the given
267   * set itself).
268   *
269   * <p><b>Note:</b> Despite what the method name suggests, if {@code elements}
270   * is an {@code ImmutableSortedSet}, it may be returned instead of a copy.
271   *
272   * <p>This method is not type-safe, as it may be called on elements that are
273   * not mutually comparable.
274   *
275   * <p>This method is safe to use even when {@code elements} is a synchronized
276   * or concurrent collection that is currently being modified by another
277   * thread.
278   *
279   * @throws ClassCastException if the elements are not mutually comparable
280   * @throws NullPointerException if any of {@code elements} is null
281   * @since 7.0 (source-compatible since 2.0)
282   */
283  public static <E> ImmutableSortedSet<E> copyOf(
284      Collection<? extends E> elements) {
285    // Hack around E not being a subtype of Comparable.
286    // Unsafe, see ImmutableSortedSetFauxverideShim.
287    @SuppressWarnings("unchecked")
288    Ordering<E> naturalOrder = (Ordering<E>) Ordering.<Comparable>natural();
289    return copyOf(naturalOrder, elements);
290  }
291
292  /**
293   * Returns an immutable sorted set containing the given elements sorted by
294   * their natural ordering. When multiple elements are equivalent according to
295   * {@code compareTo()}, only the first one specified is included.
296   *
297   * <p>This method is not type-safe, as it may be called on elements that are
298   * not mutually comparable.
299   *
300   * @throws ClassCastException if the elements are not mutually comparable
301   * @throws NullPointerException if any of {@code elements} is null
302   */
303  public static <E> ImmutableSortedSet<E> copyOf(
304      Iterator<? extends E> elements) {
305    // Hack around E not being a subtype of Comparable.
306    // Unsafe, see ImmutableSortedSetFauxverideShim.
307    @SuppressWarnings("unchecked")
308    Ordering<E> naturalOrder = (Ordering<E>) Ordering.<Comparable>natural();
309    return copyOf(naturalOrder, elements);
310  }
311
312  /**
313   * Returns an immutable sorted set containing the given elements sorted by
314   * the given {@code Comparator}. When multiple elements are equivalent
315   * according to {@code compareTo()}, only the first one specified is
316   * included.
317   *
318   * @throws NullPointerException if {@code comparator} or any of
319   *     {@code elements} is null
320   */
321  public static <E> ImmutableSortedSet<E> copyOf(
322      Comparator<? super E> comparator, Iterator<? extends E> elements) {
323    return copyOf(comparator, Lists.newArrayList(elements));
324  }
325
326  /**
327   * Returns an immutable sorted set containing the given elements sorted by
328   * the given {@code Comparator}. When multiple elements are equivalent
329   * according to {@code compare()}, only the first one specified is
330   * included. This method iterates over {@code elements} at most once.
331   *
332   * <p>Despite the method name, this method attempts to avoid actually copying
333   * the data when it is safe to do so. The exact circumstances under which a
334   * copy will or will not be performed are undocumented and subject to change.
335   *
336   * @throws NullPointerException if {@code comparator} or any of {@code
337   *         elements} is null
338   */
339  public static <E> ImmutableSortedSet<E> copyOf(
340      Comparator<? super E> comparator, Iterable<? extends E> elements) {
341    checkNotNull(comparator);
342    boolean hasSameComparator =
343        SortedIterables.hasSameComparator(comparator, elements);
344
345    if (hasSameComparator && (elements instanceof ImmutableSortedSet)) {
346      @SuppressWarnings("unchecked")
347      ImmutableSortedSet<E> original = (ImmutableSortedSet<E>) elements;
348      if (!original.isPartialView()) {
349        return original;
350      }
351    }
352    @SuppressWarnings("unchecked") // elements only contains E's; it's safe.
353    E[] array = (E[]) Iterables.toArray(elements);
354    return construct(comparator, array.length, array);
355  }
356
357  /**
358   * Returns an immutable sorted set containing the given elements sorted by
359   * the given {@code Comparator}. When multiple elements are equivalent
360   * according to {@code compareTo()}, only the first one specified is
361   * included.
362   *
363   * <p>Despite the method name, this method attempts to avoid actually copying
364   * the data when it is safe to do so. The exact circumstances under which a
365   * copy will or will not be performed are undocumented and subject to change.
366   *
367   * <p>This method is safe to use even when {@code elements} is a synchronized
368   * or concurrent collection that is currently being modified by another
369   * thread.
370   *
371   * @throws NullPointerException if {@code comparator} or any of
372   *     {@code elements} is null
373   * @since 7.0 (source-compatible since 2.0)
374   */
375  public static <E> ImmutableSortedSet<E> copyOf(
376      Comparator<? super E> comparator, Collection<? extends E> elements) {
377    return copyOf(comparator, (Iterable<? extends E>) elements);
378  }
379
380  /**
381   * Returns an immutable sorted set containing the elements of a sorted set,
382   * sorted by the same {@code Comparator}. That behavior differs from {@link
383   * #copyOf(Iterable)}, which always uses the natural ordering of the
384   * elements.
385   *
386   * <p>Despite the method name, this method attempts to avoid actually copying
387   * the data when it is safe to do so. The exact circumstances under which a
388   * copy will or will not be performed are undocumented and subject to change.
389   *
390   * <p>This method is safe to use even when {@code sortedSet} is a synchronized
391   * or concurrent collection that is currently being modified by another
392   * thread.
393   *
394   * @throws NullPointerException if {@code sortedSet} or any of its elements
395   *     is null
396   */
397  public static <E> ImmutableSortedSet<E> copyOfSorted(SortedSet<E> sortedSet) {
398    Comparator<? super E> comparator = SortedIterables.comparator(sortedSet);
399    E[] elements = (E[]) sortedSet.toArray();
400    if (elements.length == 0) {
401      return emptySet(comparator);
402    } else {
403      return new RegularImmutableSortedSet<E>(
404          ImmutableList.<E>asImmutableList(elements), comparator);
405    }
406  }
407
408  /**
409   * Sorts and eliminates duplicates from the first {@code n} positions in {@code contents}.
410   * Returns the number of unique elements.  If this returns {@code k}, then the first {@code k}
411   * elements of {@code contents} will be the sorted, unique elements, and {@code
412   * contents[i] == null} for {@code k <= i < n}.
413   *
414   * @throws NullPointerException if any of the first {@code n} elements of {@code contents} is
415   *          null
416   */
417  static <E> int sortAndUnique(
418      Comparator<? super E> comparator, int n, E... contents) {
419    if (n == 0) {
420      return 0;
421    }
422    for (int i = 0; i < n; i++) {
423      ObjectArrays.checkElementNotNull(contents[i], i);
424    }
425    Arrays.sort(contents, 0, n, comparator);
426    int uniques = 1;
427    for (int i = 1; i < n; i++) {
428      E cur = contents[i];
429      E prev = contents[uniques - 1];
430      if (comparator.compare(cur, prev) != 0) {
431        contents[uniques++] = cur;
432      }
433    }
434    Arrays.fill(contents, uniques, n, null);
435    return uniques;
436  }
437
438  /**
439   * Constructs an {@code ImmutableSortedSet} from the first {@code n} elements of
440   * {@code contents}.  If {@code k} is the size of the returned {@code ImmutableSortedSet}, then
441   * the sorted unique elements are in the first {@code k} positions of {@code contents}, and
442   * {@code contents[i] == null} for {@code k <= i < n}.
443   *
444   * <p>If {@code k == contents.length}, then {@code contents} may no longer be safe for
445   * modification.
446   *
447   * @throws NullPointerException if any of the first {@code n} elements of {@code contents} is
448   *          null
449   */
450  static <E> ImmutableSortedSet<E> construct(
451      Comparator<? super E> comparator, int n, E... contents) {
452    int uniques = sortAndUnique(comparator, n, contents);
453    if (uniques == 0) {
454      return emptySet(comparator);
455    } else if (uniques < contents.length) {
456      contents = ObjectArrays.arraysCopyOf(contents, uniques);
457    }
458    return new RegularImmutableSortedSet<E>(
459        ImmutableList.<E>asImmutableList(contents), comparator);
460  }
461
462  /**
463   * Returns a builder that creates immutable sorted sets with an explicit
464   * comparator. If the comparator has a more general type than the set being
465   * generated, such as creating a {@code SortedSet<Integer>} with a
466   * {@code Comparator<Number>}, use the {@link Builder} constructor instead.
467   *
468   * @throws NullPointerException if {@code comparator} is null
469   */
470  public static <E> Builder<E> orderedBy(Comparator<E> comparator) {
471    return new Builder<E>(comparator);
472  }
473
474  /**
475   * Returns a builder that creates immutable sorted sets whose elements are
476   * ordered by the reverse of their natural ordering.
477   *
478   * <p>Note: the type parameter {@code E} extends {@code Comparable<E>} rather
479   * than {@code Comparable<? super E>} as a workaround for javac <a
480   * href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6468354">bug
481   * 6468354</a>.
482   */
483  public static <E extends Comparable<E>> Builder<E> reverseOrder() {
484    return new Builder<E>(Ordering.natural().reverse());
485  }
486
487  /**
488   * Returns a builder that creates immutable sorted sets whose elements are
489   * ordered by their natural ordering. The sorted sets use {@link
490   * Ordering#natural()} as the comparator. This method provides more
491   * type-safety than {@link #builder}, as it can be called only for classes
492   * that implement {@link Comparable}.
493   *
494   * <p>Note: the type parameter {@code E} extends {@code Comparable<E>} rather
495   * than {@code Comparable<? super E>} as a workaround for javac <a
496   * href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6468354">bug
497   * 6468354</a>.
498   */
499  public static <E extends Comparable<E>> Builder<E> naturalOrder() {
500    return new Builder<E>(Ordering.natural());
501  }
502
503  /**
504   * A builder for creating immutable sorted set instances, especially {@code
505   * public static final} sets ("constant sets"), with a given comparator.
506   * Example: <pre>   {@code
507   *
508   *   public static final ImmutableSortedSet<Number> LUCKY_NUMBERS =
509   *       new ImmutableSortedSet.Builder<Number>(ODDS_FIRST_COMPARATOR)
510   *           .addAll(SINGLE_DIGIT_PRIMES)
511   *           .add(42)
512   *           .build();}</pre>
513   *
514   * Builder instances can be reused; it is safe to call {@link #build} multiple
515   * times to build multiple sets in series. Each set is a superset of the set
516   * created before it.
517   *
518   * @since 2.0 (imported from Google Collections Library)
519   */
520  public static final class Builder<E> extends ImmutableSet.Builder<E> {
521    private final Comparator<? super E> comparator;
522
523    /**
524     * Creates a new builder. The returned builder is equivalent to the builder
525     * generated by {@link ImmutableSortedSet#orderedBy}.
526     */
527    public Builder(Comparator<? super E> comparator) {
528      this.comparator = checkNotNull(comparator);
529    }
530
531    /**
532     * Adds {@code element} to the {@code ImmutableSortedSet}.  If the
533     * {@code ImmutableSortedSet} already contains {@code element}, then
534     * {@code add} has no effect. (only the previously added element
535     * is retained).
536     *
537     * @param element the element to add
538     * @return this {@code Builder} object
539     * @throws NullPointerException if {@code element} is null
540     */
541    @Override public Builder<E> add(E element) {
542      super.add(element);
543      return this;
544    }
545
546    /**
547     * Adds each element of {@code elements} to the {@code ImmutableSortedSet},
548     * ignoring duplicate elements (only the first duplicate element is added).
549     *
550     * @param elements the elements to add
551     * @return this {@code Builder} object
552     * @throws NullPointerException if {@code elements} contains a null element
553     */
554    @Override public Builder<E> add(E... elements) {
555      super.add(elements);
556      return this;
557    }
558
559    /**
560     * Adds each element of {@code elements} to the {@code ImmutableSortedSet},
561     * ignoring duplicate elements (only the first duplicate element is added).
562     *
563     * @param elements the elements to add to the {@code ImmutableSortedSet}
564     * @return this {@code Builder} object
565     * @throws NullPointerException if {@code elements} contains a null element
566     */
567    @Override public Builder<E> addAll(Iterable<? extends E> elements) {
568      super.addAll(elements);
569      return this;
570    }
571
572    /**
573     * Adds each element of {@code elements} to the {@code ImmutableSortedSet},
574     * ignoring duplicate elements (only the first duplicate element is added).
575     *
576     * @param elements the elements to add to the {@code ImmutableSortedSet}
577     * @return this {@code Builder} object
578     * @throws NullPointerException if {@code elements} contains a null element
579     */
580    @Override public Builder<E> addAll(Iterator<? extends E> elements) {
581      super.addAll(elements);
582      return this;
583    }
584
585    /**
586     * Returns a newly-created {@code ImmutableSortedSet} based on the contents
587     * of the {@code Builder} and its comparator.
588     */
589    @Override public ImmutableSortedSet<E> build() {
590      @SuppressWarnings("unchecked") // we're careful to put only E's in here
591      E[] contentsArray = (E[]) contents;
592      ImmutableSortedSet<E> result = construct(comparator, size, contentsArray);
593      this.size = result.size(); // we eliminated duplicates in-place in contentsArray
594      return result;
595    }
596  }
597
598  int unsafeCompare(Object a, Object b) {
599    return unsafeCompare(comparator, a, b);
600  }
601
602  static int unsafeCompare(
603      Comparator<?> comparator, Object a, Object b) {
604    // Pretend the comparator can compare anything. If it turns out it can't
605    // compare a and b, we should get a CCE on the subsequent line. Only methods
606    // that are spec'd to throw CCE should call this.
607    @SuppressWarnings("unchecked")
608    Comparator<Object> unsafeComparator = (Comparator<Object>) comparator;
609    return unsafeComparator.compare(a, b);
610  }
611
612  final transient Comparator<? super E> comparator;
613
614  ImmutableSortedSet(Comparator<? super E> comparator) {
615    this.comparator = comparator;
616  }
617
618  /**
619   * Returns the comparator that orders the elements, which is
620   * {@link Ordering#natural()} when the natural ordering of the
621   * elements is used. Note that its behavior is not consistent with
622   * {@link SortedSet#comparator()}, which returns {@code null} to indicate
623   * natural ordering.
624   */
625  @Override
626  public Comparator<? super E> comparator() {
627    return comparator;
628  }
629
630  @Override // needed to unify the iterator() methods in Collection and SortedIterable
631  public abstract UnmodifiableIterator<E> iterator();
632
633  /**
634   * {@inheritDoc}
635   *
636   * <p>This method returns a serializable {@code ImmutableSortedSet}.
637   *
638   * <p>The {@link SortedSet#headSet} documentation states that a subset of a
639   * subset throws an {@link IllegalArgumentException} if passed a
640   * {@code toElement} greater than an earlier {@code toElement}. However, this
641   * method doesn't throw an exception in that situation, but instead keeps the
642   * original {@code toElement}.
643   */
644  @Override
645  public ImmutableSortedSet<E> headSet(E toElement) {
646    return headSet(toElement, false);
647  }
648
649  /**
650   * @since 12.0
651   */
652  @GwtIncompatible("NavigableSet")
653  @Override
654  public ImmutableSortedSet<E> headSet(E toElement, boolean inclusive) {
655    return headSetImpl(checkNotNull(toElement), inclusive);
656  }
657
658  /**
659   * {@inheritDoc}
660   *
661   * <p>This method returns a serializable {@code ImmutableSortedSet}.
662   *
663   * <p>The {@link SortedSet#subSet} documentation states that a subset of a
664   * subset throws an {@link IllegalArgumentException} if passed a
665   * {@code fromElement} smaller than an earlier {@code fromElement}. However,
666   * this method doesn't throw an exception in that situation, but instead keeps
667   * the original {@code fromElement}. Similarly, this method keeps the
668   * original {@code toElement}, instead of throwing an exception, if passed a
669   * {@code toElement} greater than an earlier {@code toElement}.
670   */
671  @Override
672  public ImmutableSortedSet<E> subSet(E fromElement, E toElement) {
673    return subSet(fromElement, true, toElement, false);
674  }
675
676  /**
677   * @since 12.0
678   */
679  @GwtIncompatible("NavigableSet")
680  @Override
681  public ImmutableSortedSet<E> subSet(
682      E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
683    checkNotNull(fromElement);
684    checkNotNull(toElement);
685    checkArgument(comparator.compare(fromElement, toElement) <= 0);
686    return subSetImpl(fromElement, fromInclusive, toElement, toInclusive);
687  }
688
689  /**
690   * {@inheritDoc}
691   *
692   * <p>This method returns a serializable {@code ImmutableSortedSet}.
693   *
694   * <p>The {@link SortedSet#tailSet} documentation states that a subset of a
695   * subset throws an {@link IllegalArgumentException} if passed a
696   * {@code fromElement} smaller than an earlier {@code fromElement}. However,
697   * this method doesn't throw an exception in that situation, but instead keeps
698   * the original {@code fromElement}.
699   */
700  @Override
701  public ImmutableSortedSet<E> tailSet(E fromElement) {
702    return tailSet(fromElement, true);
703  }
704
705  /**
706   * @since 12.0
707   */
708  @GwtIncompatible("NavigableSet")
709  @Override
710  public ImmutableSortedSet<E> tailSet(E fromElement, boolean inclusive) {
711    return tailSetImpl(checkNotNull(fromElement), inclusive);
712  }
713
714  /*
715   * These methods perform most headSet, subSet, and tailSet logic, besides
716   * parameter validation.
717   */
718  abstract ImmutableSortedSet<E> headSetImpl(E toElement, boolean inclusive);
719
720  abstract ImmutableSortedSet<E> subSetImpl(
721      E fromElement, boolean fromInclusive, E toElement, boolean toInclusive);
722
723  abstract ImmutableSortedSet<E> tailSetImpl(E fromElement, boolean inclusive);
724
725  /**
726   * @since 12.0
727   */
728  @GwtIncompatible("NavigableSet")
729  @Override
730  public E lower(E e) {
731    return Iterables.getFirst(headSet(e, false).descendingSet(), null);
732  }
733
734  /**
735   * @since 12.0
736   */
737  @GwtIncompatible("NavigableSet")
738  @Override
739  public E floor(E e) {
740    return Iterables.getFirst(headSet(e, true).descendingSet(), null);
741  }
742
743  /**
744   * @since 12.0
745   */
746  @GwtIncompatible("NavigableSet")
747  @Override
748  public E ceiling(E e) {
749    return Iterables.getFirst(tailSet(e, true), null);
750  }
751
752  /**
753   * @since 12.0
754   */
755  @GwtIncompatible("NavigableSet")
756  @Override
757  public E higher(E e) {
758    return Iterables.getFirst(tailSet(e, false), null);
759  }
760
761  /**
762   * @since 12.0
763   */
764  @GwtIncompatible("NavigableSet")
765  @Override
766  public final E pollFirst() {
767    throw new UnsupportedOperationException();
768  }
769
770  /**
771   * @since 12.0
772   */
773  @GwtIncompatible("NavigableSet")
774  @Override
775  public final E pollLast() {
776    throw new UnsupportedOperationException();
777  }
778
779  @GwtIncompatible("NavigableSet")
780  transient ImmutableSortedSet<E> descendingSet;
781
782  /**
783   * @since 12.0
784   */
785  @GwtIncompatible("NavigableSet")
786  @Override
787  public ImmutableSortedSet<E> descendingSet() {
788    ImmutableSortedSet<E> result = descendingSet;
789    if (result == null) {
790      result = descendingSet = createDescendingSet();
791      result.descendingSet = this;
792    }
793    return result;
794  }
795
796  @GwtIncompatible("NavigableSet")
797  abstract ImmutableSortedSet<E> createDescendingSet();
798
799  /**
800   * @since 12.0
801   */
802  @GwtIncompatible("NavigableSet")
803  @Override
804  public UnmodifiableIterator<E> descendingIterator() {
805    return descendingSet().iterator();
806  }
807
808  /**
809   * Returns the position of an element within the set, or -1 if not present.
810   */
811  abstract int indexOf(@Nullable Object target);
812
813  /*
814   * This class is used to serialize all ImmutableSortedSet instances,
815   * regardless of implementation type. It captures their "logical contents"
816   * only. This is necessary to ensure that the existence of a particular
817   * implementation type is an implementation detail.
818   */
819  private static class SerializedForm<E> implements Serializable {
820    final Comparator<? super E> comparator;
821    final Object[] elements;
822
823    public SerializedForm(Comparator<? super E> comparator, Object[] elements) {
824      this.comparator = comparator;
825      this.elements = elements;
826    }
827
828    @SuppressWarnings("unchecked")
829    Object readResolve() {
830      return new Builder<E>(comparator).add((E[]) elements).build();
831    }
832
833    private static final long serialVersionUID = 0;
834  }
835
836  private void readObject(ObjectInputStream stream)
837      throws InvalidObjectException {
838    throw new InvalidObjectException("Use SerializedForm");
839  }
840
841  @Override Object writeReplace() {
842    return new SerializedForm<E>(comparator, toArray());
843  }
844}
845