    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 *
    046 * @since 4.0
    047 */
    048public class IndexedCollection<K, C> extends AbstractCollectionDecorator<C> {
    049
    050    // TODO: replace with MultiValuedMap
    051
    052    /** Serialization version */
    053    private static final long serialVersionUID = -5512610452568370038L;
    054
    055    /**
    056     * Create an {@link IndexedCollection} for a non-unique index.
    057     *
    058     * @param <K> the index object type.
    059     * @param <C> the collection type.
    060     * @param coll the decorated {@link Collection}.
    061     * @param keyTransformer the {@link Transformer} for generating index keys.
    062     * @return the created {@link IndexedCollection}.
    063     */
    064    public static <K, C> IndexedCollection<K, C> nonUniqueIndexedCollection(final Collection<C> coll,
    065                                                                            final Transformer<C, K> keyTransformer) {
    066        return new IndexedCollection<>(coll, keyTransformer,
    067                                           MultiValueMap.<K, C>multiValueMap(new HashMap<>()),
    068                                           false);
    069    }
    070
    071    /**
    072     * Create an {@link IndexedCollection} for a unique index.
    073     * <p>
    074     * If an element is added, which maps to an existing key, an {@link IllegalArgumentException}
    075     * will be thrown.
    076     *
    077     * @param <K> the index object type.
    078     * @param <C> the collection type.
    079     * @param coll the decorated {@link Collection}.
    080     * @param keyTransformer the {@link Transformer} for generating index keys.
    081     * @return the created {@link IndexedCollection}.
    082     */
    083    public static <K, C> IndexedCollection<K, C> uniqueIndexedCollection(final Collection<C> coll,
    084                                                                         final Transformer<C, K> keyTransformer) {
    085        return new IndexedCollection<>(coll, keyTransformer,
    086                                           MultiValueMap.<K, C>multiValueMap(new HashMap<>()),
    087                                           true);
    088    }
    089
    090    /** The {@link Transformer} for generating index keys. */
    091    private final Transformer<C, K> keyTransformer;
    092
    093    /** The map of indexes to collected objects. */
    094    private final MultiMap<K, C> index;
    095
    096    /** The uniqueness constraint for the index. */
    097    private final boolean uniqueIndex;
    098
    099    /**
    100     * Create a {@link IndexedCollection}.
    101     *
    102     * @param coll  decorated {@link Collection}
    103     * @param keyTransformer  {@link Transformer} for generating index keys
    104     * @param map  map to use as index
    105     * @param uniqueIndex  if the index shall enforce uniqueness of index keys
    106     */
    107    public IndexedCollection(final Collection<C> coll, final Transformer<C, K> keyTransformer,
    108                             final MultiMap<K, C> map, final boolean uniqueIndex) {
    109        super(coll);
    110        this.keyTransformer = keyTransformer;
    111        this.index = map;
    112        this.uniqueIndex = uniqueIndex;
    113        reindex();
    114    }
    115
    116    /**
    117     * {@inheritDoc}
    118     *
    119     * @throws IllegalArgumentException if the object maps to an existing key and the index
    120     *   enforces a uniqueness constraint
    121     */
    122    @Override
    123    public boolean add(final C object) {
    124        final boolean added = super.add(object);
    125        if (added) {
    126            addToIndex(object);
    127        }
    128        return added;
    129    }
    130
    131    @Override
    132    public boolean addAll(final Collection<? extends C> coll) {
    133        boolean changed = false;
    134        for (final C c: coll) {
    135            changed |= add(c);
    136        }
    137        return changed;
    138    }
    139
    140    /**
    141     * Provides checking for adding the index.
    142     *
    143     * @param object the object to index
    144     * @throws IllegalArgumentException if the object maps to an existing key and the index
    145     *   enforces a uniqueness constraint
    146     */
    147    private void addToIndex(final C object) {
    148        final K key = keyTransformer.transform(object);
    149        if (uniqueIndex && index.containsKey(key)) {
    150            throw new IllegalArgumentException("Duplicate key in uniquely indexed collection.");
    151        }
    152        index.put(key, object);
    153    }
    154
    155    @Override
    156    public void clear() {
    157        super.clear();
    158        index.clear();
    159    }
    160
    161    /**
    162     * {@inheritDoc}
    163     * <p>
    164     * Note: uses the index for fast lookup
    165     */
    166    @SuppressWarnings("unchecked")
    167    @Override
    168    public boolean contains(final Object object) {
    169        return index.containsKey(keyTransformer.transform((C) object));
    170    }
    171
    172    /**
    173     * {@inheritDoc}
    174     * <p>
    175     * Note: uses the index for fast lookup
    176     */
    177    @Override
    178    public boolean containsAll(final Collection<?> coll) {
    179        for (final Object o : coll) {
    180            if (!contains(o)) {
    181                return false;
    182            }
    183        }
    184        return true;
    185    }
    186
    187    /**
    188     * Gets the element associated with the given key.
    189     * <p>
    190     * In case of a non-unique index, this method will return the first
    191     * value associated with the given key. To retrieve all elements associated
    192     * with a key, use {@link #values(Object)}.
    193     *
    194     * @param key  key to look up
    195     * @return element found
    196     * @see #values(Object)
    197     */
    198    public C get(final K key) {
    199        @SuppressWarnings("unchecked") // index is a MultiMap which returns a Collection
    200        final Collection<C> coll = (Collection<C>) index.get(key);
    201        return coll == null ? null : coll.iterator().next();
    202    }
    203
    204    /**
    205     * Clears the index and re-indexes the entire decorated {@link Collection}.
    206     */
    207    public void reindex() {
    208        index.clear();
    209        for (final C c : decorated()) {
    210            addToIndex(c);
    211        }
    212    }
    213
    214    @SuppressWarnings("unchecked")
    215    @Override
    216    public boolean remove(final Object object) {
    217        final boolean removed = super.remove(object);
    218        if (removed) {
    219            removeFromIndex((C) object);
    220        }
    221        return removed;
    222    }
    223
    224    @Override
    225    public boolean removeAll(final Collection<?> coll) {
    226        boolean changed = false;
    227        for (final Object o : coll) {
    228            changed |= remove(o);
    229        }
    230        return changed;
    231    }
    232
    233    /**
    234     * Removes an object from the index.
    235     *
    236     * @param object the object to remove
    237     */
    238    private void removeFromIndex(final C object) {
    239        index.remove(keyTransformer.transform(object));
    240    }
    241
    242    /**
    243     * @since 4.4
    244     */
    245    @Override
    246    public boolean removeIf(final Predicate<? super C> filter) {
    247        if (Objects.isNull(filter)) {
    248            return false;
    249        }
    250        boolean changed = false;
    251        final Iterator<C> it = iterator();
    252        while (it.hasNext()) {
    253            if (filter.test(it.next())) {
    254                it.remove();
    255                changed = true;
    256            }
    257        }
    258        if (changed) {
    259            reindex();
    260        }
    261        return changed;
    262    }
    263
    264    @Override
    265    public boolean retainAll(final Collection<?> coll) {
    266        final boolean changed = super.retainAll(coll);
    267        if (changed) {
    268            reindex();
    269        }
    270        return changed;
    271    }
    272
    273    /**
    274     * Gets all elements associated with the given key.
    275     *
    276     * @param key  key to look up
    277     * @return a collection of elements found, or null if {@code contains(key) == false}
    278     */
    279    @SuppressWarnings("unchecked") // index is a MultiMap which returns a Collection
    280    public Collection<C> values(final K key) {
    281        return (Collection<C>) index.get(key);
    282    }
    283
    284}