001/*
002 * Copyright (C) 2011 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
005 * use this file except in compliance with the License. You may obtain a copy of
006 * 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, WITHOUT
012 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
013 * License for the specific language governing permissions and limitations under
014 * the License.
015 */
016
017package com.google.common.collect;
018
019import com.google.common.annotations.GwtCompatible;
020import java.util.Collection;
021import java.util.Comparator;
022import java.util.Iterator;
023import java.util.NavigableSet;
024import java.util.Set;
025import javax.annotation.CheckForNull;
026import org.checkerframework.checker.nullness.qual.Nullable;
027
028/**
029 * A {@link Multiset} which maintains the ordering of its elements, according to either their
030 * natural order or an explicit {@link Comparator}. This order is reflected when iterating over the
031 * sorted multiset, either directly, or through its {@code elementSet} or {@code entrySet} views. In
032 * all cases, this implementation uses {@link Comparable#compareTo} or {@link Comparator#compare}
033 * instead of {@link Object#equals} to determine equivalence of instances.
034 *
035 * <p><b>Warning:</b> The comparison must be <i>consistent with equals</i> as explained by the
036 * {@link Comparable} class specification. Otherwise, the resulting multiset will violate the {@link
037 * Collection} contract, which is specified in terms of {@link Object#equals}.
038 *
039 * <p>See the Guava User Guide article on <a href=
040 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#multiset">{@code Multiset}</a>.
041 *
042 * @author Louis Wasserman
043 * @since 11.0
044 */
045@GwtCompatible(emulated = true)
046@ElementTypesAreNonnullByDefault
047public interface SortedMultiset<E extends @Nullable Object>
048    extends SortedMultisetBridge<E>, SortedIterable<E> {
049  /**
050   * Returns the comparator that orders this multiset, or {@link Ordering#natural()} if the natural
051   * ordering of the elements is used.
052   */
053  @Override
054  Comparator<? super E> comparator();
055
056  /**
057   * Returns the entry of the first element in this multiset, or {@code null} if this multiset is
058   * empty.
059   */
060  @CheckForNull
061  Entry<E> firstEntry();
062
063  /**
064   * Returns the entry of the last element in this multiset, or {@code null} if this multiset is
065   * empty.
066   */
067  @CheckForNull
068  Entry<E> lastEntry();
069
070  /**
071   * Returns and removes the entry associated with the lowest element in this multiset, or returns
072   * {@code null} if this multiset is empty.
073   */
074  @CheckForNull
075  Entry<E> pollFirstEntry();
076
077  /**
078   * Returns and removes the entry associated with the greatest element in this multiset, or returns
079   * {@code null} if this multiset is empty.
080   */
081  @CheckForNull
082  Entry<E> pollLastEntry();
083
084  /**
085   * Returns a {@link NavigableSet} view of the distinct elements in this multiset.
086   *
087   * @since 14.0 (present with return type {@code SortedSet} since 11.0)
088   */
089  @Override
090  NavigableSet<E> elementSet();
091
092  /**
093   * {@inheritDoc}
094   *
095   * <p>The {@code entrySet}'s iterator returns entries in ascending element order according to the
096   * this multiset's comparator.
097   */
098  @Override
099  Set<Entry<E>> entrySet();
100
101  /**
102   * {@inheritDoc}
103   *
104   * <p>The iterator returns the elements in ascending order according to this multiset's
105   * comparator.
106   */
107  @Override
108  Iterator<E> iterator();
109
110  /**
111   * Returns a descending view of this multiset. Modifications made to either map will be reflected
112   * in the other.
113   */
114  SortedMultiset<E> descendingMultiset();
115
116  /**
117   * Returns a view of this multiset restricted to the elements less than {@code upperBound},
118   * optionally including {@code upperBound} itself. The returned multiset is a view of this
119   * multiset, so changes to one will be reflected in the other. The returned multiset supports all
120   * operations that this multiset supports.
121   *
122   * <p>The returned multiset will throw an {@link IllegalArgumentException} on attempts to add
123   * elements outside its range.
124   */
125  SortedMultiset<E> headMultiset(@ParametricNullness E upperBound, BoundType boundType);
126
127  /**
128   * Returns a view of this multiset restricted to the range between {@code lowerBound} and {@code
129   * upperBound}. The returned multiset is a view of this multiset, so changes to one will be
130   * reflected in the other. The returned multiset supports all operations that this multiset
131   * supports.
132   *
133   * <p>The returned multiset will throw an {@link IllegalArgumentException} on attempts to add
134   * elements outside its range.
135   *
136   * <p>This method is equivalent to {@code tailMultiset(lowerBound,
137   * lowerBoundType).headMultiset(upperBound, upperBoundType)}.
138   */
139  SortedMultiset<E> subMultiset(
140      @ParametricNullness E lowerBound,
141      BoundType lowerBoundType,
142      @ParametricNullness E upperBound,
143      BoundType upperBoundType);
144
145  /**
146   * Returns a view of this multiset restricted to the elements greater than {@code lowerBound},
147   * optionally including {@code lowerBound} itself. The returned multiset is a view of this
148   * multiset, so changes to one will be reflected in the other. The returned multiset supports all
149   * operations that this multiset supports.
150   *
151   * <p>The returned multiset will throw an {@link IllegalArgumentException} on attempts to add
152   * elements outside its range.
153   */
154  SortedMultiset<E> tailMultiset(@ParametricNullness E lowerBound, BoundType boundType);
155}