    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 *      http://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.collection;
    018
    019import java.util.Collection;
    020import java.util.HashMap;
    021import java.util.Iterator;
    022import java.util.Objects;
    023import java.util.function.Predicate;
    024
    025import org.apache.commons.collections4.MultiMap;
    026import org.apache.commons.collections4.Transformer;
    027import org.apache.commons.collections4.map.MultiValueMap;
    028
    029/**
    030 * An IndexedCollection is a Map-like view onto a Collection. It accepts a
    031 * keyTransformer to define how the keys are converted from the values.
    032 * <p>
    033 * Modifications made to this decorator modify the index as well as the
    034 * decorated {@link Collection}. However, modifications to the underlying
    035 * {@link Collection} will not update the index and it will get out of sync.
    036 * </p>
    037 * <p>
    038 * If modification of the decorated {@link Collection} is unavoidable, then a
    039 * call to {@link #reindex()} will update the index to the current contents of
    040 * the {@link Collection}.
    041 * </p>
    042 *
    043 * @param <K> the type of object in the index.
    044 * @param <C> the type of object in the collection.
    045 * @since 4.0
    046 */
    047public class IndexedCollection<K, C> extends AbstractCollectionDecorator<C> {
    048
    049    // TODO: replace with MultiValuedMap
    050
    051    /** Serialization version */
    052    private static final long serialVersionUID = -5512610452568370038L;
    053
    054    /**
    055     * Create an {@link IndexedCollection} for a non-unique index.
    056     *
    057     * @param <K> the index object type.
    058     * @param <C> the collection type.
    059     * @param coll the decorated {@link Collection}.
    060     * @param keyTransformer the {@link Transformer} for generating index keys.
    061     * @return the created {@link IndexedCollection}.
    062     */
    063    public static <K, C> IndexedCollection<K, C> nonUniqueIndexedCollection(final Collection<C> coll,
    064                                                                            final Transformer<C, K> keyTransformer) {
    065        return new IndexedCollection<>(coll, keyTransformer,
    066                                           MultiValueMap.<K, C>multiValueMap(new HashMap<>()),
    067                                           false);
    068    }
    069
    070    /**
    071     * Create an {@link IndexedCollection} for a unique index.
    072     * <p>
    073     * If an element is added, which maps to an existing key, an {@link IllegalArgumentException}
    074     * will be thrown.
    075     *
    076     * @param <K> the index object type.
    077     * @param <C> the collection type.
    078     * @param coll the decorated {@link Collection}.
    079     * @param keyTransformer the {@link Transformer} for generating index keys.
    080     * @return the created {@link IndexedCollection}.
    081     */
    082    public static <K, C> IndexedCollection<K, C> uniqueIndexedCollection(final Collection<C> coll,
    083                                                                         final Transformer<C, K> keyTransformer) {
    084        return new IndexedCollection<>(coll, keyTransformer,
    085                                           MultiValueMap.<K, C>multiValueMap(new HashMap<>()),
    086                                           true);
    087    }
    088
    089    /** The {@link Transformer} for generating index keys. */
    090    private final Transformer<C, K> keyTransformer;
    091
    092    /** The map of indexes to collected objects. */
    093    private final MultiMap<K, C> index;
    094
    095    /** The uniqueness constraint for the index. */
    096    private final boolean uniqueIndex;
    097
    098    /**
    099     * Create a {@link IndexedCollection}.
    100     *
    101     * @param coll  decorated {@link Collection}
    102     * @param keyTransformer  {@link Transformer} for generating index keys
    103     * @param map  map to use as index
    104     * @param uniqueIndex  if the index shall enforce uniqueness of index keys
    105     */
    106    public IndexedCollection(final Collection<C> coll, final Transformer<C, K> keyTransformer,
    107                             final MultiMap<K, C> map, final boolean uniqueIndex) {
    108        super(coll);
    109        this.keyTransformer = keyTransformer;
    110        this.index = map;
    111        this.uniqueIndex = uniqueIndex;
    112        reindex();
    113    }
    114
    115    /**
    116     * {@inheritDoc}
    117     *
    118     * @throws IllegalArgumentException if the object maps to an existing key and the index
    119     *   enforces a uniqueness constraint
    120     */
    121    @Override
    122    public boolean add(final C object) {
    123        final boolean added = super.add(object);
    124        if (added) {
    125            addToIndex(object);
    126        }
    127        return added;
    128    }
    129
    130    @Override
    131    public boolean addAll(final Collection<? extends C> coll) {
    132        boolean changed = false;
    133        for (final C c: coll) {
    134            changed |= add(c);
    135        }
    136        return changed;
    137    }
    138
    139    /**
    140     * Provides checking for adding the index.
    141     *
    142     * @param object the object to index
    143     * @throws IllegalArgumentException if the object maps to an existing key and the index
    144     *   enforces a uniqueness constraint
    145     */
    146    private void addToIndex(final C object) {
    147        final K key = keyTransformer.apply(object);
    148        if (uniqueIndex && index.containsKey(key)) {
    149            throw new IllegalArgumentException("Duplicate key in uniquely indexed collection.");
    150        }
    151        index.put(key, object);
    152    }
    153
    154    @Override
    155    public void clear() {
    156        super.clear();
    157        index.clear();
    158    }
    159
    160    /**
    161     * {@inheritDoc}
    162     * <p>
    163     * Note: uses the index for fast lookup
    164     */
    165    @SuppressWarnings("unchecked")
    166    @Override
    167    public boolean contains(final Object object) {
    168        return index.containsKey(keyTransformer.apply((C) object));
    169    }
    170
    171    /**
    172     * {@inheritDoc}
    173     * <p>
    174     * Note: uses the index for fast lookup
    175     */
    176    @Override
    177    public boolean containsAll(final Collection<?> coll) {
    178        for (final Object o : coll) {
    179            if (!contains(o)) {
    180                return false;
    181            }
    182        }
    183        return true;
    184    }
    185
    186    /**
    187     * Gets the element associated with the given key.
    188     * <p>
    189     * In case of a non-unique index, this method will return the first
    190     * value associated with the given key. To retrieve all elements associated
    191     * with a key, use {@link #values(Object)}.
    192     *
    193     * @param key  key to look up
    194     * @return element found
    195     * @see #values(Object)
    196     */
    197    public C get(final K key) {
    198        @SuppressWarnings("unchecked") // index is a MultiMap which returns a Collection
    199        final Collection<C> coll = (Collection<C>) index.get(key);
    200        return coll == null ? null : coll.iterator().next();
    201    }
    202
    203    /**
    204     * Clears the index and re-indexes the entire decorated {@link Collection}.
    205     */
    206    public void reindex() {
    207        index.clear();
    208        for (final C c : decorated()) {
    209            addToIndex(c);
    210        }
    211    }
    212
    213    @SuppressWarnings("unchecked")
    214    @Override
    215    public boolean remove(final Object object) {
    216        final boolean removed = super.remove(object);
    217        if (removed) {
    218            removeFromIndex((C) object);
    219        }
    220        return removed;
    221    }
    222
    223    @Override
    224    public boolean removeAll(final Collection<?> coll) {
    225        boolean changed = false;
    226        for (final Object o : coll) {
    227            changed |= remove(o);
    228        }
    229        return changed;
    230    }
    231
    232    /**
    233     * Removes an object from the index.
    234     *
    235     * @param object the object to remove
    236     */
    237    private void removeFromIndex(final C object) {
    238        index.remove(keyTransformer.apply(object));
    239    }
    240
    241    /**
    242     * @since 4.4
    243     */
    244    @Override
    245    public boolean removeIf(final Predicate<? super C> filter) {
    246        if (Objects.isNull(filter)) {
    247            return false;
    248        }
    249        boolean changed = false;
    250        final Iterator<C> it = iterator();
    251        while (it.hasNext()) {
    252            if (filter.test(it.next())) {
    253                it.remove();
    254                changed = true;
    255            }
    256        }
    257        if (changed) {
    258            reindex();
    259        }
    260        return changed;
    261    }
    262
    263    @Override
    264    public boolean retainAll(final Collection<?> coll) {
    265        final boolean changed = super.retainAll(coll);
    266        if (changed) {
    267            reindex();
    268        }
    269        return changed;
    270    }
    271
    272    /**
    273     * Gets all elements associated with the given key.
    274     *
    275     * @param key  key to look up
    276     * @return a collection of elements found, or null if {@code contains(key) == false}
    277     */
    278    @SuppressWarnings("unchecked") // index is a MultiMap which returns a Collection
    279    public Collection<C> values(final K key) {
    280        return (Collection<C>) index.get(key);
    281    }
    282
    283}