    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
    017    package com.google.common.collect;
    018
    019    import static com.google.common.base.Preconditions.checkArgument;
    020    import static com.google.common.base.Preconditions.checkNotNull;
    021
    022    import com.google.common.annotations.GwtCompatible;
    023    import com.google.common.annotations.GwtIncompatible;
    024
    025    import java.io.InvalidObjectException;
    026    import java.io.ObjectInputStream;
    027    import java.io.Serializable;
    028    import java.util.ArrayList;
    029    import java.util.Arrays;
    030    import java.util.Collection;
    031    import java.util.Collections;
    032    import java.util.Comparator;
    033    import java.util.Iterator;
    034    import java.util.List;
    035    import java.util.NavigableSet;
    036    import java.util.SortedSet;
    037
    038    import 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
    095    public 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