Source code

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;
021import static com.google.common.collect.ObjectArrays.checkElementsNotNull;
022
023import com.google.common.annotations.GwtCompatible;
024import com.google.common.annotations.GwtIncompatible;
025import com.google.errorprone.annotations.CanIgnoreReturnValue;
026import com.google.errorprone.annotations.DoNotCall;
027import com.google.errorprone.annotations.concurrent.LazyInit;
028import java.io.InvalidObjectException;
029import java.io.ObjectInputStream;
030import java.io.Serializable;
031import java.util.Arrays;
032import java.util.Collection;
033import java.util.Collections;
034import java.util.Comparator;
035import java.util.Iterator;
036import java.util.NavigableSet;
037import java.util.SortedSet;
038import java.util.Spliterator;
039import java.util.Spliterators;
040import java.util.function.Consumer;
041import java.util.stream.Collector;
042import javax.annotation.CheckForNull;
043import org.checkerframework.checker.nullness.qual.Nullable;
044
045/**
046 * A {@link NavigableSet} whose contents will never change, with many other important properties
047 * detailed at {@link ImmutableCollection}.
048 *
049 * <p><b>Warning:</b> as with any sorted collection, you are strongly advised not to use a {@link
050 * Comparator} or {@link Comparable} type whose comparison behavior is <i>inconsistent with
051 * equals</i>. That is, {@code a.compareTo(b)} or {@code comparator.compare(a, b)} should equal zero
052 * <i>if and only if</i> {@code a.equals(b)}. If this advice is not followed, the resulting
053 * collection will not correctly obey its specification.
054 *
055 * <p>See the Guava User Guide article on <a href=
056 * "https://github.com/google/guava/wiki/ImmutableCollectionsExplained"> immutable collections</a>.
057 *
058 * @author Jared Levy
059 * @author Louis Wasserman
060 * @since 2.0 (implements {@code NavigableSet} since 12.0)
061 */
062// TODO(benyu): benchmark and optimize all creation paths, which are a mess now
063@GwtCompatible(serializable = true, emulated = true)
064@SuppressWarnings("serial") // we're overriding default serialization
065@ElementTypesAreNonnullByDefault
066public abstract class ImmutableSortedSet<E> extends ImmutableSortedSetFauxverideShim<E>
067    implements NavigableSet<E>, SortedIterable<E> {
068  static final int SPLITERATOR_CHARACTERISTICS =
069      ImmutableSet.SPLITERATOR_CHARACTERISTICS | Spliterator.SORTED;
070
071  /**
072   * Returns a {@code Collector} that accumulates the input elements into a new {@code
073   * ImmutableSortedSet}, ordered by the specified comparator.
074   *
075   * <p>If the elements contain duplicates (according to the comparator), only the first duplicate
076   * in encounter order will appear in the result.
077   *
078   * @since 21.0
079   */
080  public static <E> Collector<E, ?, ImmutableSortedSet<E>> toImmutableSortedSet(
081      Comparator<? super E> comparator) {
082    return CollectCollectors.toImmutableSortedSet(comparator);
083  }
084
085  static <E> RegularImmutableSortedSet<E> emptySet(Comparator<? super E> comparator) {
086    if (Ordering.natural().equals(comparator)) {
087      return (RegularImmutableSortedSet<E>) RegularImmutableSortedSet.NATURAL_EMPTY_SET;
088    } else {
089      return new RegularImmutableSortedSet<E>(ImmutableList.<E>of(), comparator);
090    }
091  }
092
093  /**
094   * Returns the empty immutable sorted set.
095   *
096   * <p><b>Performance note:</b> the instance returned is a singleton.
097   */
098  public static <E> ImmutableSortedSet<E> of() {
099    return (ImmutableSortedSet<E>) RegularImmutableSortedSet.NATURAL_EMPTY_SET;
100  }
101
102  /** Returns an immutable sorted set containing a single element. */
103  public static <E extends Comparable<? super E>> ImmutableSortedSet<E> of(E element) {
104    return new RegularImmutableSortedSet<E>(ImmutableList.of(element), Ordering.natural());
105  }
106
107  /**
108   * Returns an immutable sorted set containing the given elements sorted by their natural ordering.
109   * When multiple elements are equivalent according to {@link Comparable#compareTo}, only the first
110   * one specified is included.
111   *
112   * @throws NullPointerException if any element is null
113   */
114  @SuppressWarnings("unchecked")
115  public static <E extends Comparable<? super E>> ImmutableSortedSet<E> of(E e1, E e2) {
116    return construct(Ordering.natural(), 2, e1, e2);
117  }
118
119  /**
120   * Returns an immutable sorted set containing the given elements sorted by their natural ordering.
121   * When multiple elements are equivalent according to {@link Comparable#compareTo}, only the first
122   * one specified is included.
123   *
124   * @throws NullPointerException if any element is null
125   */
126  @SuppressWarnings("unchecked")
127  public static <E extends Comparable<? super E>> ImmutableSortedSet<E> of(E e1, E e2, E e3) {
128    return construct(Ordering.natural(), 3, e1, e2, e3);
129  }
130
131  /**
132   * Returns an immutable sorted set containing the given elements sorted by their natural ordering.
133   * When multiple elements are equivalent according to {@link Comparable#compareTo}, only the first
134   * one specified is included.
135   *
136   * @throws NullPointerException if any element is null
137   */
138  @SuppressWarnings("unchecked")
139  public static <E extends Comparable<? super E>> ImmutableSortedSet<E> of(E e1, E e2, E e3, E e4) {
140    return construct(Ordering.natural(), 4, e1, e2, e3, e4);
141  }
142
143  /**
144   * Returns an immutable sorted set containing the given elements sorted by their natural ordering.
145   * When multiple elements are equivalent according to {@link Comparable#compareTo}, only the first
146   * one specified is included.
147   *
148   * @throws NullPointerException if any element is null
149   */
150  @SuppressWarnings("unchecked")
151  public static <E extends Comparable<? super E>> ImmutableSortedSet<E> of(
152      E e1, E e2, E e3, E e4, E e5) {
153    return construct(Ordering.natural(), 5, e1, e2, e3, e4, e5);
154  }
155
156  /**
157   * Returns an immutable sorted set containing the given elements sorted by their natural ordering.
158   * When multiple elements are equivalent according to {@link Comparable#compareTo}, only the first
159   * one specified is included.
160   *
161   * @throws NullPointerException if any element is null
162   * @since 3.0 (source-compatible since 2.0)
163   */
164  @SuppressWarnings("unchecked")
165  public static <E extends Comparable<? super E>> ImmutableSortedSet<E> of(
166      E e1, E e2, E e3, E e4, E e5, E e6, E... remaining) {
167    Comparable[] contents = new Comparable[6 + remaining.length];
168    contents[0] = e1;
169    contents[1] = e2;
170    contents[2] = e3;
171    contents[3] = e4;
172    contents[4] = e5;
173    contents[5] = e6;
174    System.arraycopy(remaining, 0, contents, 6, remaining.length);
175    return construct(Ordering.natural(), contents.length, (E[]) contents);
176  }
177
178  // TODO(kevinb): Consider factory methods that reject duplicates
179
180  /**
181   * Returns an immutable sorted set containing the given elements sorted by their natural ordering.
182   * When multiple elements are equivalent according to {@link Comparable#compareTo}, only the first
183   * one specified is included.
184   *
185   * @throws NullPointerException if any of {@code elements} is null
186   * @since 3.0
187   */
188  public static <E extends Comparable<? super E>> ImmutableSortedSet<E> copyOf(E[] elements) {
189    return construct(Ordering.natural(), elements.length, elements.clone());
190  }
191
192  /**
193   * Returns an immutable sorted set containing the given elements sorted by their natural ordering.
194   * When multiple elements are equivalent according to {@code compareTo()}, only the first one
195   * specified is included. To create a copy of a {@code SortedSet} that preserves the comparator,
196   * call {@link #copyOfSorted} instead. This method iterates over {@code elements} at most once.
197   *
198   * <p>Note that if {@code s} is a {@code Set<String>}, then {@code ImmutableSortedSet.copyOf(s)}
199   * returns an {@code ImmutableSortedSet<String>} containing each of the strings in {@code s},
200   * while {@code ImmutableSortedSet.of(s)} returns an {@code ImmutableSortedSet<Set<String>>}
201   * containing one element (the given set itself).
202   *
203   * <p>Despite the method name, this method attempts to avoid actually copying the data when it is
204   * safe to do so. The exact circumstances under which a copy will or will not be performed are
205   * undocumented and subject to change.
206   *
207   * <p>This method is not type-safe, as it may be called on elements that are not mutually
208   * comparable.
209   *
210   * @throws ClassCastException if the elements are not mutually comparable
211   * @throws NullPointerException if any of {@code elements} is null
212   */
213  public static <E> ImmutableSortedSet<E> copyOf(Iterable<? extends E> elements) {
214    // Hack around E not being a subtype of Comparable.
215    // Unsafe, see ImmutableSortedSetFauxverideShim.
216    @SuppressWarnings("unchecked")
217    Ordering<E> naturalOrder = (Ordering<E>) Ordering.<Comparable>natural();
218    return copyOf(naturalOrder, elements);
219  }
220
221  /**
222   * Returns an immutable sorted set containing the given elements sorted by their natural ordering.
223   * When multiple elements are equivalent according to {@code compareTo()}, only the first one
224   * specified is included. To create a copy of a {@code SortedSet} that preserves the comparator,
225   * call {@link #copyOfSorted} instead. This method iterates over {@code elements} at most once.
226   *
227   * <p>Note that if {@code s} is a {@code Set<String>}, then {@code ImmutableSortedSet.copyOf(s)}
228   * returns an {@code ImmutableSortedSet<String>} containing each of the strings in {@code s},
229   * while {@code ImmutableSortedSet.of(s)} returns an {@code ImmutableSortedSet<Set<String>>}
230   * containing one element (the given set itself).
231   *
232   * <p><b>Note:</b> Despite what the method name suggests, if {@code elements} is an {@code
233   * ImmutableSortedSet}, it may be returned instead of a copy.
234   *
235   * <p>This method is not type-safe, as it may be called on elements that are not mutually
236   * comparable.
237   *
238   * <p>This method is safe to use even when {@code elements} is a synchronized or concurrent
239   * collection that is currently being modified by another thread.
240   *
241   * @throws ClassCastException if the elements are not mutually comparable
242   * @throws NullPointerException if any of {@code elements} is null
243   * @since 7.0 (source-compatible since 2.0)
244   */
245  public static <E> ImmutableSortedSet<E> copyOf(Collection<? extends E> elements) {
246    // Hack around E not being a subtype of Comparable.
247    // Unsafe, see ImmutableSortedSetFauxverideShim.
248    @SuppressWarnings("unchecked")
249    Ordering<E> naturalOrder = (Ordering<E>) Ordering.<Comparable>natural();
250    return copyOf(naturalOrder, elements);
251  }
252
253  /**
254   * Returns an immutable sorted set containing the given elements sorted by their natural ordering.
255   * When multiple elements are equivalent according to {@code compareTo()}, only the first one
256   * specified is included.
257   *
258   * <p>This method is not type-safe, as it may be called on elements that are not mutually
259   * comparable.
260   *
261   * @throws ClassCastException if the elements are not mutually comparable
262   * @throws NullPointerException if any of {@code elements} is null
263   */
264  public static <E> ImmutableSortedSet<E> copyOf(Iterator<? extends E> elements) {
265    // Hack around E not being a subtype of Comparable.
266    // Unsafe, see ImmutableSortedSetFauxverideShim.
267    @SuppressWarnings("unchecked")
268    Ordering<E> naturalOrder = (Ordering<E>) Ordering.<Comparable>natural();
269    return copyOf(naturalOrder, elements);
270  }
271
272  /**
273   * Returns an immutable sorted set containing the given elements sorted by the given {@code
274   * Comparator}. When multiple elements are equivalent according to {@code compareTo()}, only the
275   * first one specified is included.
276   *
277   * @throws NullPointerException if {@code comparator} or any of {@code elements} is null
278   */
279  public static <E> ImmutableSortedSet<E> copyOf(
280      Comparator<? super E> comparator, Iterator<? extends E> elements) {
281    return new Builder<E>(comparator).addAll(elements).build();
282  }
283
284  /**
285   * Returns an immutable sorted set containing the given elements sorted by the given {@code
286   * Comparator}. When multiple elements are equivalent according to {@code compare()}, only the
287   * first one specified is included. This method iterates over {@code elements} at most once.
288   *
289   * <p>Despite the method name, this method attempts to avoid actually copying the data when it is
290   * safe to do so. The exact circumstances under which a copy will or will not be performed are
291   * undocumented and subject to change.
292   *
293   * @throws NullPointerException if {@code comparator} or any of {@code elements} is null
294   */
295  public static <E> ImmutableSortedSet<E> copyOf(
296      Comparator<? super E> comparator, Iterable<? extends E> elements) {
297    checkNotNull(comparator);
298    boolean hasSameComparator = SortedIterables.hasSameComparator(comparator, elements);
299
300    if (hasSameComparator && (elements instanceof ImmutableSortedSet)) {
301      @SuppressWarnings("unchecked")
302      ImmutableSortedSet<E> original = (ImmutableSortedSet<E>) elements;
303      if (!original.isPartialView()) {
304        return original;
305      }
306    }
307    @SuppressWarnings("unchecked") // elements only contains E's; it's safe.
308    E[] array = (E[]) Iterables.toArray(elements);
309    return construct(comparator, array.length, array);
310  }
311
312  /**
313   * Returns an immutable sorted set containing the given elements sorted by the given {@code
314   * Comparator}. When multiple elements are equivalent according to {@code compareTo()}, only the
315   * first one specified is included.
316   *
317   * <p>Despite the method name, this method attempts to avoid actually copying the data when it is
318   * safe to do so. The exact circumstances under which a copy will or will not be performed are
319   * undocumented and subject to change.
320   *
321   * <p>This method is safe to use even when {@code elements} is a synchronized or concurrent
322   * collection that is currently being modified by another thread.
323   *
324   * @throws NullPointerException if {@code comparator} or any of {@code elements} is null
325   * @since 7.0 (source-compatible since 2.0)
326   */
327  public static <E> ImmutableSortedSet<E> copyOf(
328      Comparator<? super E> comparator, Collection<? extends E> elements) {
329    return copyOf(comparator, (Iterable<? extends E>) elements);
330  }
331
332  /**
333   * Returns an immutable sorted set containing the elements of a sorted set, sorted by the same
334   * {@code Comparator}. That behavior differs from {@link #copyOf(Iterable)}, which always uses the
335   * natural ordering of the elements.
336   *
337   * <p>Despite the method name, this method attempts to avoid actually copying the data when it is
338   * safe to do so. The exact circumstances under which a copy will or will not be performed are
339   * undocumented and subject to change.
340   *
341   * <p>This method is safe to use even when {@code sortedSet} is a synchronized or concurrent
342   * collection that is currently being modified by another thread.
343   *
344   * @throws NullPointerException if {@code sortedSet} or any of its elements is null
345   */
346  public static <E> ImmutableSortedSet<E> copyOfSorted(SortedSet<E> sortedSet) {
347    Comparator<? super E> comparator = SortedIterables.comparator(sortedSet);
348    ImmutableList<E> list = ImmutableList.copyOf(sortedSet);
349    if (list.isEmpty()) {
350      return emptySet(comparator);
351    } else {
352      return new RegularImmutableSortedSet<E>(list, comparator);
353    }
354  }
355
356  /**
357   * Constructs an {@code ImmutableSortedSet} from the first {@code n} elements of {@code contents}.
358   * If {@code k} is the size of the returned {@code ImmutableSortedSet}, then the sorted unique
359   * elements are in the first {@code k} positions of {@code contents}, and {@code contents[i] ==
360   * null} for {@code k <= i < n}.
361   *
362   * <p>If {@code k == contents.length}, then {@code contents} may no longer be safe for
363   * modification.
364   *
365   * @throws NullPointerException if any of the first {@code n} elements of {@code contents} is null
366   */
367  static <E> ImmutableSortedSet<E> construct(
368      Comparator<? super E> comparator, int n, E... contents) {
369    if (n == 0) {
370      return emptySet(comparator);
371    }
372    checkElementsNotNull(contents, n);
373    Arrays.sort(contents, 0, n, comparator);
374    int uniques = 1;
375    for (int i = 1; i < n; i++) {
376      E cur = contents[i];
377      E prev = contents[uniques - 1];
378      if (comparator.compare(cur, prev) != 0) {
379        contents[uniques++] = cur;
380      }
381    }
382    Arrays.fill(contents, uniques, n, null);
383    return new RegularImmutableSortedSet<E>(
384        ImmutableList.<E>asImmutableList(contents, uniques), comparator);
385  }
386
387  /**
388   * Returns a builder that creates immutable sorted sets with an explicit comparator. If the
389   * comparator has a more general type than the set being generated, such as creating a {@code
390   * SortedSet<Integer>} with a {@code Comparator<Number>}, use the {@link Builder} constructor
391   * instead.
392   *
393   * @throws NullPointerException if {@code comparator} is null
394   */
395  public static <E> Builder<E> orderedBy(Comparator<E> comparator) {
396    return new Builder<E>(comparator);
397  }
398
399  /**
400   * Returns a builder that creates immutable sorted sets whose elements are ordered by the reverse
401   * of their natural ordering.
402   */
403  public static <E extends Comparable<?>> Builder<E> reverseOrder() {
404    return new Builder<E>(Collections.reverseOrder());
405  }
406
407  /**
408   * Returns a builder that creates immutable sorted sets whose elements are ordered by their
409   * natural ordering. The sorted sets use {@link Ordering#natural()} as the comparator. This method
410   * provides more type-safety than {@link #builder}, as it can be called only for classes that
411   * implement {@link Comparable}.
412   */
413  public static <E extends Comparable<?>> Builder<E> naturalOrder() {
414    return new Builder<E>(Ordering.natural());
415  }
416
417  /**
418   * A builder for creating immutable sorted set instances, especially {@code public static final}
419   * sets ("constant sets"), with a given comparator. Example:
420   *
421   * <pre>{@code
422   * public static final ImmutableSortedSet<Number> LUCKY_NUMBERS =
423   *     new ImmutableSortedSet.Builder<Number>(ODDS_FIRST_COMPARATOR)
424   *         .addAll(SINGLE_DIGIT_PRIMES)
425   *         .add(42)
426   *         .build();
427   * }</pre>
428   *
429   * <p>Builder instances can be reused; it is safe to call {@link #build} multiple times to build
430   * multiple sets in series. Each set is a superset of the set created before it.
431   *
432   * @since 2.0
433   */
434  public static final class Builder<E> extends ImmutableSet.Builder<E> {
435    private final Comparator<? super E> comparator;
436    private E[] elements;
437    private int n;
438
439    /**
440     * Creates a new builder. The returned builder is equivalent to the builder generated by {@link
441     * ImmutableSortedSet#orderedBy}.
442     */
443    public Builder(Comparator<? super E> comparator) {
444      super(true); // don't construct guts of hash-based set builder
445      this.comparator = checkNotNull(comparator);
446      this.elements = (E[]) new Object[ImmutableCollection.Builder.DEFAULT_INITIAL_CAPACITY];
447      this.n = 0;
448    }
449
450    @Override
451    void copy() {
452      elements = Arrays.copyOf(elements, elements.length);
453    }
454
455    private void sortAndDedup() {
456      if (n == 0) {
457        return;
458      }
459      Arrays.sort(elements, 0, n, comparator);
460      int unique = 1;
461      for (int i = 1; i < n; i++) {
462        int cmp = comparator.compare(elements[unique - 1], elements[i]);
463        if (cmp < 0) {
464          elements[unique++] = elements[i];
465        } else if (cmp > 0) {
466          throw new AssertionError(
467              "Comparator " + comparator + " compare method violates its contract");
468        }
469      }
470      Arrays.fill(elements, unique, n, null);
471      n = unique;
472    }
473
474    /**
475     * Adds {@code element} to the {@code ImmutableSortedSet}. If the {@code ImmutableSortedSet}
476     * already contains {@code element}, then {@code add} has no effect. (only the previously added
477     * element is retained).
478     *
479     * @param element the element to add
480     * @return this {@code Builder} object
481     * @throws NullPointerException if {@code element} is null
482     */
483    @CanIgnoreReturnValue
484    @Override
485    public Builder<E> add(E element) {
486      checkNotNull(element);
487      copyIfNecessary();
488      if (n == elements.length) {
489        sortAndDedup();
490        /*
491         * Sorting operations can only be allowed to occur once every O(n) operations to keep
492         * amortized O(n log n) performance.  Therefore, ensure there are at least O(n) *unused*
493         * spaces in the builder array.
494         */
495        int newLength = ImmutableCollection.Builder.expandedCapacity(n, n + 1);
496        if (newLength > elements.length) {
497          elements = Arrays.copyOf(elements, newLength);
498        }
499      }
500      elements[n++] = element;
501      return this;
502    }
503
504    /**
505     * Adds each element of {@code elements} to the {@code ImmutableSortedSet}, ignoring duplicate
506     * elements (only the first duplicate element is added).
507     *
508     * @param elements the elements to add
509     * @return this {@code Builder} object
510     * @throws NullPointerException if {@code elements} contains a null element
511     */
512    @CanIgnoreReturnValue
513    @Override
514    public Builder<E> add(E... elements) {
515      checkElementsNotNull(elements);
516      for (E e : elements) {
517        add(e);
518      }
519      return this;
520    }
521
522    /**
523     * Adds each element of {@code elements} to the {@code ImmutableSortedSet}, ignoring duplicate
524     * elements (only the first duplicate element is added).
525     *
526     * @param elements the elements to add to the {@code ImmutableSortedSet}
527     * @return this {@code Builder} object
528     * @throws NullPointerException if {@code elements} contains a null element
529     */
530    @CanIgnoreReturnValue
531    @Override
532    public Builder<E> addAll(Iterable<? extends E> elements) {
533      super.addAll(elements);
534      return this;
535    }
536
537    /**
538     * Adds each element of {@code elements} to the {@code ImmutableSortedSet}, ignoring duplicate
539     * elements (only the first duplicate element is added).
540     *
541     * @param elements the elements to add to the {@code ImmutableSortedSet}
542     * @return this {@code Builder} object
543     * @throws NullPointerException if {@code elements} contains a null element
544     */
545    @CanIgnoreReturnValue
546    @Override
547    public Builder<E> addAll(Iterator<? extends E> elements) {
548      super.addAll(elements);
549      return this;
550    }
551
552    @CanIgnoreReturnValue
553    @Override
554    Builder<E> combine(ImmutableSet.Builder<E> builder) {
555      copyIfNecessary();
556      Builder<E> other = (Builder<E>) builder;
557      for (int i = 0; i < other.n; i++) {
558        add(other.elements[i]);
559      }
560      return this;
561    }
562
563    /**
564     * Returns a newly-created {@code ImmutableSortedSet} based on the contents of the {@code
565     * Builder} and its comparator.
566     */
567    @Override
568    public ImmutableSortedSet<E> build() {
569      sortAndDedup();
570      if (n == 0) {
571        return emptySet(comparator);
572      } else {
573        forceCopy = true;
574        return new RegularImmutableSortedSet<E>(
575            ImmutableList.asImmutableList(elements, n), comparator);
576      }
577    }
578  }
579
580  int unsafeCompare(Object a, @CheckForNull Object b) {
581    return unsafeCompare(comparator, a, b);
582  }
583
584  static int unsafeCompare(Comparator<?> comparator, Object a, @CheckForNull Object b) {
585    // Pretend the comparator can compare anything. If it turns out it can't
586    // compare a and b, we should get a CCE or NPE on the subsequent line. Only methods
587    // that are spec'd to throw CCE and NPE should call this.
588    @SuppressWarnings({"unchecked", "nullness"})
589    Comparator<@Nullable Object> unsafeComparator = (Comparator<@Nullable Object>) comparator;
590    return unsafeComparator.compare(a, b);
591  }
592
593  final transient Comparator<? super E> comparator;
594
595  ImmutableSortedSet(Comparator<? super E> comparator) {
596    this.comparator = comparator;
597  }
598
599  /**
600   * Returns the comparator that orders the elements, which is {@link Ordering#natural()} when the
601   * natural ordering of the elements is used. Note that its behavior is not consistent with {@link
602   * SortedSet#comparator()}, which returns {@code null} to indicate natural ordering.
603   */
604  @Override
605  public Comparator<? super E> comparator() {
606    return comparator;
607  }
608
609  @Override // needed to unify the iterator() methods in Collection and SortedIterable
610  public abstract UnmodifiableIterator<E> iterator();
611
612  /**
613   * {@inheritDoc}
614   *
615   * <p>This method returns a serializable {@code ImmutableSortedSet}.
616   *
617   * <p>The {@link SortedSet#headSet} documentation states that a subset of a subset throws an
618   * {@link IllegalArgumentException} if passed a {@code toElement} greater than an earlier {@code
619   * toElement}. However, this method doesn't throw an exception in that situation, but instead
620   * keeps the original {@code toElement}.
621   */
622  @Override
623  public ImmutableSortedSet<E> headSet(E toElement) {
624    return headSet(toElement, false);
625  }
626
627  /** @since 12.0 */
628  @Override
629  public ImmutableSortedSet<E> headSet(E toElement, boolean inclusive) {
630    return headSetImpl(checkNotNull(toElement), inclusive);
631  }
632
633  /**
634   * {@inheritDoc}
635   *
636   * <p>This method returns a serializable {@code ImmutableSortedSet}.
637   *
638   * <p>The {@link SortedSet#subSet} documentation states that a subset of a subset throws an {@link
639   * IllegalArgumentException} if passed a {@code fromElement} smaller than an earlier {@code
640   * fromElement}. However, this method doesn't throw an exception in that situation, but instead
641   * keeps the original {@code fromElement}. Similarly, this method keeps the original {@code
642   * toElement}, instead of throwing an exception, if passed a {@code toElement} greater than an
643   * earlier {@code toElement}.
644   */
645  @Override
646  public ImmutableSortedSet<E> subSet(E fromElement, E toElement) {
647    return subSet(fromElement, true, toElement, false);
648  }
649
650  /** @since 12.0 */
651  @GwtIncompatible // NavigableSet
652  @Override
653  public ImmutableSortedSet<E> subSet(
654      E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
655    checkNotNull(fromElement);
656    checkNotNull(toElement);
657    checkArgument(comparator.compare(fromElement, toElement) <= 0);
658    return subSetImpl(fromElement, fromInclusive, toElement, toInclusive);
659  }
660
661  /**
662   * {@inheritDoc}
663   *
664   * <p>This method returns a serializable {@code ImmutableSortedSet}.
665   *
666   * <p>The {@link SortedSet#tailSet} documentation states that a subset of a subset throws an
667   * {@link IllegalArgumentException} if passed a {@code fromElement} smaller than an earlier {@code
668   * fromElement}. However, this method doesn't throw an exception in that situation, but instead
669   * keeps the original {@code fromElement}.
670   */
671  @Override
672  public ImmutableSortedSet<E> tailSet(E fromElement) {
673    return tailSet(fromElement, true);
674  }
675
676  /** @since 12.0 */
677  @Override
678  public ImmutableSortedSet<E> tailSet(E fromElement, boolean inclusive) {
679    return tailSetImpl(checkNotNull(fromElement), inclusive);
680  }
681
682  /*
683   * These methods perform most headSet, subSet, and tailSet logic, besides
684   * parameter validation.
685   */
686  abstract ImmutableSortedSet<E> headSetImpl(E toElement, boolean inclusive);
687
688  abstract ImmutableSortedSet<E> subSetImpl(
689      E fromElement, boolean fromInclusive, E toElement, boolean toInclusive);
690
691  abstract ImmutableSortedSet<E> tailSetImpl(E fromElement, boolean inclusive);
692
693  /** @since 12.0 */
694  @GwtIncompatible // NavigableSet
695  @Override
696  @CheckForNull
697  public E lower(E e) {
698    return Iterators.getNext(headSet(e, false).descendingIterator(), null);
699  }
700
701  /** @since 12.0 */
702  @Override
703  @CheckForNull
704  public E floor(E e) {
705    return Iterators.getNext(headSet(e, true).descendingIterator(), null);
706  }
707
708  /** @since 12.0 */
709  @Override
710  @CheckForNull
711  public E ceiling(E e) {
712    return Iterables.getFirst(tailSet(e, true), null);
713  }
714
715  /** @since 12.0 */
716  @GwtIncompatible // NavigableSet
717  @Override
718  @CheckForNull
719  public E higher(E e) {
720    return Iterables.getFirst(tailSet(e, false), null);
721  }
722
723  @Override
724  public E first() {
725    return iterator().next();
726  }
727
728  @Override
729  public E last() {
730    return descendingIterator().next();
731  }
732
733  /**
734   * Guaranteed to throw an exception and leave the set unmodified.
735   *
736   * @since 12.0
737   * @throws UnsupportedOperationException always
738   * @deprecated Unsupported operation.
739   */
740  @CanIgnoreReturnValue
741  @Deprecated
742  @GwtIncompatible // NavigableSet
743  @Override
744  @DoNotCall("Always throws UnsupportedOperationException")
745  @CheckForNull
746  public final E pollFirst() {
747    throw new UnsupportedOperationException();
748  }
749
750  /**
751   * Guaranteed to throw an exception and leave the set unmodified.
752   *
753   * @since 12.0
754   * @throws UnsupportedOperationException always
755   * @deprecated Unsupported operation.
756   */
757  @CanIgnoreReturnValue
758  @Deprecated
759  @GwtIncompatible // NavigableSet
760  @Override
761  @DoNotCall("Always throws UnsupportedOperationException")
762  @CheckForNull
763  public final E pollLast() {
764    throw new UnsupportedOperationException();
765  }
766
767  @GwtIncompatible // NavigableSet
768  @LazyInit
769  @CheckForNull
770  transient ImmutableSortedSet<E> descendingSet;
771
772  /** @since 12.0 */
773  @GwtIncompatible // NavigableSet
774  @Override
775  public ImmutableSortedSet<E> descendingSet() {
776    // racy single-check idiom
777    ImmutableSortedSet<E> result = descendingSet;
778    if (result == null) {
779      result = descendingSet = createDescendingSet();
780      result.descendingSet = this;
781    }
782    return result;
783  }
784
785  // Most classes should implement this as new DescendingImmutableSortedSet<E>(this),
786  // but we push down that implementation because ProGuard can't eliminate it even when it's always
787  // overridden.
788  @GwtIncompatible // NavigableSet
789  abstract ImmutableSortedSet<E> createDescendingSet();
790
791  @Override
792  public Spliterator<E> spliterator() {
793    return new Spliterators.AbstractSpliterator<E>(
794        size(), SPLITERATOR_CHARACTERISTICS | Spliterator.SIZED) {
795      final UnmodifiableIterator<E> iterator = iterator();
796
797      @Override
798      public boolean tryAdvance(Consumer<? super E> action) {
799        if (iterator.hasNext()) {
800          action.accept(iterator.next());
801          return true;
802        } else {
803          return false;
804        }
805      }
806
807      @Override
808      public Comparator<? super E> getComparator() {
809        return comparator;
810      }
811    };
812  }
813
814  /** @since 12.0 */
815  @GwtIncompatible // NavigableSet
816  @Override
817  public abstract UnmodifiableIterator<E> descendingIterator();
818
819  /** Returns the position of an element within the set, or -1 if not present. */
820  abstract int indexOf(@CheckForNull Object target);
821
822  /*
823   * This class is used to serialize all ImmutableSortedSet instances,
824   * regardless of implementation type. It captures their "logical contents"
825   * only. This is necessary to ensure that the existence of a particular
826   * implementation type is an implementation detail.
827   */
828  private static class SerializedForm<E> implements Serializable {
829    final Comparator<? super E> comparator;
830    final Object[] elements;
831
832    public SerializedForm(Comparator<? super E> comparator, Object[] elements) {
833      this.comparator = comparator;
834      this.elements = elements;
835    }
836
837    @SuppressWarnings("unchecked")
838    Object readResolve() {
839      return new Builder<E>(comparator).add((E[]) elements).build();
840    }
841
842    private static final long serialVersionUID = 0;
843  }
844
845  private void readObject(ObjectInputStream unused) throws InvalidObjectException {
846    throw new InvalidObjectException("Use SerializedForm");
847  }
848
849  @Override
850  Object writeReplace() {
851    return new SerializedForm<E>(comparator, toArray());
852  }
853}