    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      https://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.collections4.multiset;
    018
    019import java.io.IOException;
    020import java.io.ObjectInputStream;
    021import java.io.ObjectOutputStream;
    022import java.io.Serializable;
    023import java.util.Collection;
    024import java.util.Comparator;
    025import java.util.Objects;
    026import java.util.SortedMap;
    027import java.util.TreeMap;
    028
    029import org.apache.commons.collections4.SortedMultiSet;
    030
    031/**
    032 * Implements {@link SortedMultiSet}, using a {@link TreeMap} to provide the
    033 * data storage. This is the standard implementation of a sorted multiset.
    034 * <p>
    035 * Order will be maintained among the multiset members and can be viewed
    036 * through the iterator.
    037 * </p>
    038 * <p>
    039 * A {@code MultiSet} stores each object in the collection together with a
    040 * count of occurrences. Extra methods on the interface allow multiple copies
    041 * of an object to be added or removed at once.
    042 * </p>
    043 * <p>
    044 * <strong>Note that TreeMultiSet is not synchronized and is not thread-safe.</strong>
    045 * If you wish to use this multiset from multiple threads concurrently, you must use
    046 * appropriate synchronization. The simplest approach is to wrap this multiset using
    047 * {@link org.apache.commons.collections4.MultiSetUtils#synchronizedSortedMultiSet(SortedMultiSet)}.
    048 * Unsynchronized concurrent modification can corrupt the structure of the backing
    049 * {@link TreeMap}, and a malformed tree may cause subsequent operations, including
    050 * reads, to enter an infinite loop.
    051 * </p>
    052 *
    053 * @param <E> The type held in the multiset
    054 * @since 4.6.0
    055 */
    056public class TreeMultiSet<E> extends AbstractMapMultiSet<E> implements SortedMultiSet<E>, Serializable {
    057
    058    /** Serial version lock */
    059    private static final long serialVersionUID = 20260705L;
    060
    061    /**
    062     * Constructs an empty {@link TreeMultiSet}.
    063     */
    064    public TreeMultiSet() {
    065        super(new TreeMap<>());
    066    }
    067
    068    /**
    069     * Constructs a {@link TreeMultiSet} containing all the members of the
    070     * specified collection.
    071     *
    072     * @param coll The collection to copy into the multiset
    073     */
    074    public TreeMultiSet(final Collection<? extends E> coll) {
    075        this();
    076        addAll(coll);
    077    }
    078
    079    /**
    080     * Constructs an empty multiset that maintains order on its unique representative
    081     * members according to the given {@link Comparator}.
    082     *
    083     * @param comparator The comparator to use
    084     */
    085    public TreeMultiSet(final Comparator<? super E> comparator) {
    086        super(new TreeMap<>(comparator));
    087    }
    088
    089    /**
    090     * Constructs a multiset containing all the members of the given Iterable.
    091     *
    092     * @param iterable An iterable to copy into this multiset.
    093     * @since 4.6.0
    094     */
    095    public TreeMultiSet(final Iterable<? extends E> iterable) {
    096        super(new TreeMap<>(), iterable);
    097    }
    098
    099    /**
    100     * {@inheritDoc}
    101     *
    102     * @throws IllegalArgumentException if the object to be added does not implement
    103     * {@link Comparable} and the {@link TreeMultiSet} is using natural ordering
    104     * @throws NullPointerException if the specified key is null and this multiset uses
    105     * natural ordering, or its comparator does not permit null keys
    106     */
    107    @Override
    108    public int add(final E object, final int occurrences) {
    109        if (comparator() == null && !(object instanceof Comparable)) {
    110            Objects.requireNonNull(object, "object");
    111            throw new IllegalArgumentException("Objects of type " + object.getClass() + " cannot be added to " +
    112                                               "a naturally ordered TreeMultiSet as it does not implement Comparable");
    113        }
    114        return super.add(object, occurrences);
    115    }
    116
    117    @Override
    118    public Comparator<? super E> comparator() {
    119        return getMap().comparator();
    120    }
    121
    122    @Override
    123    public E first() {
    124        return getMap().firstKey();
    125    }
    126
    127    @Override
    128    protected SortedMap<E, AbstractMapMultiSet.MutableInteger> getMap() {
    129        return (SortedMap<E, AbstractMapMultiSet.MutableInteger>) super.getMap();
    130    }
    131
    132    @Override
    133    public E last() {
    134        return getMap().lastKey();
    135    }
    136
    137    /**
    138     * Deserializes the multiset in using a custom routine.
    139     *
    140     * @param in  The input stream
    141     * @throws IOException Thrown if an error occurs while reading from the stream
    142     * @throws ClassNotFoundException if an object read from the stream cannot be loaded
    143     */
    144    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
    145        in.defaultReadObject();
    146        @SuppressWarnings("unchecked")  // This will fail at runtime if the stream is incorrect
    147        final Comparator<? super E> comp = (Comparator<? super E>) in.readObject();
    148        setMap(new TreeMap<>(comp));
    149        super.doReadObject(in);
    150    }
    151
    152    /**
    153     * Serializes this object to an ObjectOutputStream.
    154     *
    155     * @param out The target ObjectOutputStream.
    156     * @throws IOException thrown when an I/O errors occur writing to the target stream.
    157     */
    158    private void writeObject(final ObjectOutputStream out) throws IOException {
    159        out.defaultWriteObject();
    160        out.writeObject(comparator());
    161        super.doWriteObject(out);
    162    }
    163
    164}