guava/src/com/google/common/collect/SortedMultiset.java

/*
 * Copyright (C) 2011 The Guava Authors
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;

import java.util.Collection;
import java.util.Comparator;
import java.util.Iterator;
import java.util.NavigableSet;
import java.util.Set;

/**
 * A {@link Multiset} which maintains the ordering of its elements, according to
 * either their natural order or an explicit {@link Comparator}. This order is
 * reflected when iterating over the sorted multiset, either directly, or through
 * its {@code elementSet} or {@code entrySet} views.  In all cases,
 * this implementation uses {@link Comparable#compareTo} or
 * {@link Comparator#compare} instead of {@link Object#equals} to determine
 * equivalence of instances.
 * 
 * <p><b>Warning:</b> The comparison must be <i>consistent with equals</i> as
 * explained by the {@link Comparable} class specification. Otherwise, the
 * resulting multiset will violate the {@link Collection} contract, which it is
 * specified in terms of {@link Object#equals}.
 * 
 * <p>See the Guava User Guide article on <a href=
 * "http://code.google.com/p/guava-libraries/wiki/NewCollectionTypesExplained#Multiset">
 * {@code Multiset}</a>.
 * 
 * @author Louis Wasserman
 * @since 11.0
 */
@Beta
@GwtCompatible(emulated = true)
public interface SortedMultiset<E> extends SortedMultisetBridge<E>, SortedIterable<E> {
  /**
   * Returns the comparator that orders this multiset, or
   * {@link Ordering#natural()} if the natural ordering of the elements is used.
   */
  Comparator<? super E> comparator();

  /**
   * Returns the entry of the first element in this multiset, or {@code null} if
   * this multiset is empty.
   */
  Entry<E> firstEntry();

  /**
   * Returns the entry of the last element in this multiset, or {@code null} if
   * this multiset is empty.
   */
  Entry<E> lastEntry();

  /**
   * Returns and removes the entry associated with the lowest element in this
   * multiset, or returns {@code null} if this multiset is empty.
   */
  Entry<E> pollFirstEntry();

  /**
   * Returns and removes the entry associated with the greatest element in this
   * multiset, or returns {@code null} if this multiset is empty.
   */
  Entry<E> pollLastEntry();

  /**
   * Returns a {@link NavigableSet} view of the distinct elements in this multiset.
   * 
   * @since 14.0 (present with return type {@code SortedSet} since 11.0)
   */
  @Override NavigableSet<E> elementSet();
  
  /**
   * {@inheritDoc}
   *
   * <p>The {@code entrySet}'s iterator returns entries in ascending element
   * order according to the this multiset's comparator.
   */
  @Override Set<Entry<E>> entrySet();

  /**
   * {@inheritDoc}
   *
   * <p>The iterator returns the elements in ascending order according to this
   * multiset's comparator.
   */
  @Override Iterator<E> iterator();

  /**
   * Returns a descending view of this multiset. Modifications made to either
   * map will be reflected in the other.
   */
  SortedMultiset<E> descendingMultiset();

  /**
   * Returns a view of this multiset restricted to the elements less than
   * {@code upperBound}, optionally including {@code upperBound} itself. The
   * returned multiset is a view of this multiset, so changes to one will be
   * reflected in the other. The returned multiset supports all operations that
   * this multiset supports.
   * 
   * <p>The returned multiset will throw an {@link IllegalArgumentException} on
   * attempts to add elements outside its range.
   */
  SortedMultiset<E> headMultiset(E upperBound, BoundType boundType);

  /**
   * Returns a view of this multiset restricted to the range between
   * {@code lowerBound} and {@code upperBound}. The returned multiset is a view
   * of this multiset, so changes to one will be reflected in the other. The
   * returned multiset supports all operations that this multiset supports.
   * 
   * <p>The returned multiset will throw an {@link IllegalArgumentException} on
   * attempts to add elements outside its range.
   * 
   * <p>This method is equivalent to
   * {@code tailMultiset(lowerBound, lowerBoundType).headMultiset(upperBound,
   * upperBoundType)}.
   */
  SortedMultiset<E> subMultiset(E lowerBound, BoundType lowerBoundType,
      E upperBound, BoundType upperBoundType);

  /**
   * Returns a view of this multiset restricted to the elements greater than
   * {@code lowerBound}, optionally including {@code lowerBound} itself. The
   * returned multiset is a view of this multiset, so changes to one will be
   * reflected in the other. The returned multiset supports all operations that
   * this multiset supports.
   * 
   * <p>The returned multiset will throw an {@link IllegalArgumentException} on
   * attempts to add elements outside its range.
   */
  SortedMultiset<E> tailMultiset(E lowerBound, BoundType boundType);
}