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
041 * Multiset}</a>.
042 *
043 * @author Louis Wasserman
044 * @since 11.0
045 */
046@GwtCompatible(emulated = true)
047@ElementTypesAreNonnullByDefault
048public interface SortedMultiset<E extends @Nullable Object>
049    extends SortedMultisetBridge<E>, SortedIterable<E> {
050  /**
051   * Returns the comparator that orders this multiset, or {@link Ordering#natural()} if the natural
052   * ordering of the elements is used.
053   */
054  @Override
055  Comparator<? super E> comparator();
056
057  /**
058   * Returns the entry of the first element in this multiset, or {@code null} if this multiset is
059   * empty.
060   */
061  @CheckForNull
062  Entry<E> firstEntry();
063
064  /**
065   * Returns the entry of the last element in this multiset, or {@code null} if this multiset is
066   * empty.
067   */
068  @CheckForNull
069  Entry<E> lastEntry();
070
071  /**
072   * Returns and removes the entry associated with the lowest element in this multiset, or returns
073   * {@code null} if this multiset is empty.
074   */
075  @CheckForNull
076  Entry<E> pollFirstEntry();
077
078  /**
079   * Returns and removes the entry associated with the greatest element in this multiset, or returns
080   * {@code null} if this multiset is empty.
081   */
082  @CheckForNull
083  Entry<E> pollLastEntry();
084
085  /**
086   * Returns a {@link NavigableSet} view of the distinct elements in this multiset.
087   *
088   * @since 14.0 (present with return type {@code SortedSet} since 11.0)
089   */
090  @Override
091  NavigableSet<E> elementSet();
092
093  /**
094   * {@inheritDoc}
095   *
096   * <p>The {@code entrySet}'s iterator returns entries in ascending element order according to the
097   * this multiset's comparator.
098   */
099  @Override
100  Set<Entry<E>> entrySet();
101
102  /**
103   * {@inheritDoc}
104   *
105   * <p>The iterator returns the elements in ascending order according to this multiset's
106   * comparator.
107   */
108  @Override
109  Iterator<E> iterator();
110
111  /**
112   * Returns a descending view of this multiset. Modifications made to either map will be reflected
113   * in the other.
114   */
115  SortedMultiset<E> descendingMultiset();
116
117  /**
118   * Returns a view of this multiset restricted to the elements less than {@code upperBound},
119   * optionally including {@code upperBound} itself. The returned multiset is a view of this
120   * multiset, so changes to one will be reflected in the other. The returned multiset supports all
121   * operations that this multiset supports.
122   *
123   * <p>The returned multiset will throw an {@link IllegalArgumentException} on attempts to add
124   * elements outside its range.
125   */
126  SortedMultiset<E> headMultiset(@ParametricNullness E upperBound, BoundType boundType);
127
128  /**
129   * Returns a view of this multiset restricted to the range between {@code lowerBound} and {@code
130   * upperBound}. The returned multiset is a view of this multiset, so changes to one will be
131   * reflected in the other. The returned multiset supports all operations that this multiset
132   * supports.
133   *
134   * <p>The returned multiset will throw an {@link IllegalArgumentException} on attempts to add
135   * elements outside its range.
136   *
137   * <p>This method is equivalent to {@code tailMultiset(lowerBound,
138   * lowerBoundType).headMultiset(upperBound, upperBoundType)}.
139   */
140  SortedMultiset<E> subMultiset(
141      @ParametricNullness E lowerBound,
142      BoundType lowerBoundType,
143      @ParametricNullness E upperBound,
144      BoundType upperBoundType);
145
146  /**
147   * Returns a view of this multiset restricted to the elements greater than {@code lowerBound},
148   * optionally including {@code lowerBound} itself. The returned multiset is a view of this
149   * multiset, so changes to one will be reflected in the other. The returned multiset supports all
150   * operations that this multiset supports.
151   *
152   * <p>The returned multiset will throw an {@link IllegalArgumentException} on attempts to add
153   * elements outside its range.
154   */
155  SortedMultiset<E> tailMultiset(@ParametricNullness E lowerBound, BoundType boundType);
156}