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