    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    /** The {@link Transformer} for generating index keys. */
    056    private final Transformer<C, K> keyTransformer;
    057
    058    /** The map of indexes to collected objects. */
    059    private final MultiMap<K, C> index;
    060
    061    /** The uniqueness constraint for the index. */
    062    private final boolean uniqueIndex;
    063
    064    /**
    065     * Create an {@link IndexedCollection} for a unique index.
    066     * <p>
    067     * If an element is added, which maps to an existing key, an {@link IllegalArgumentException}
    068     * will be thrown.
    069     *
    070     * @param <K> the index object type.
    071     * @param <C> the collection type.
    072     * @param coll the decorated {@link Collection}.
    073     * @param keyTransformer the {@link Transformer} for generating index keys.
    074     * @return the created {@link IndexedCollection}.
    075     */
    076    public static <K, C> IndexedCollection<K, C> uniqueIndexedCollection(final Collection<C> coll,
    077                                                                         final Transformer<C, K> keyTransformer) {
    078        return new IndexedCollection<>(coll, keyTransformer,
    079                                           MultiValueMap.<K, C>multiValueMap(new HashMap<K, Collection<C>>()),
    080                                           true);
    081    }
    082
    083    /**
    084     * Create an {@link IndexedCollection} for a non-unique index.
    085     *
    086     * @param <K> the index object type.
    087     * @param <C> the collection type.
    088     * @param coll the decorated {@link Collection}.
    089     * @param keyTransformer the {@link Transformer} for generating index keys.
    090     * @return the created {@link IndexedCollection}.
    091     */
    092    public static <K, C> IndexedCollection<K, C> nonUniqueIndexedCollection(final Collection<C> coll,
    093                                                                            final Transformer<C, K> keyTransformer) {
    094        return new IndexedCollection<>(coll, keyTransformer,
    095                                           MultiValueMap.<K, C>multiValueMap(new HashMap<K, Collection<C>>()),
    096                                           false);
    097    }
    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    @Override
    141    public void clear() {
    142        super.clear();
    143        index.clear();
    144    }
    145
    146    /**
    147     * {@inheritDoc}
    148     * <p>
    149     * Note: uses the index for fast lookup
    150     */
    151    @SuppressWarnings("unchecked")
    152    @Override
    153    public boolean contains(final Object object) {
    154        return index.containsKey(keyTransformer.transform((C) object));
    155    }
    156
    157    /**
    158     * {@inheritDoc}
    159     * <p>
    160     * Note: uses the index for fast lookup
    161     */
    162    @Override
    163    public boolean containsAll(final Collection<?> coll) {
    164        for (final Object o : coll) {
    165            if (!contains(o)) {
    166                return false;
    167            }
    168        }
    169        return true;
    170    }
    171
    172    /**
    173     * Get the element associated with the given key.
    174     * <p>
    175     * In case of a non-unique index, this method will return the first
    176     * value associated with the given key. To retrieve all elements associated
    177     * with a key, use {@link #values(Object)}.
    178     *
    179     * @param key  key to look up
    180     * @return element found
    181     * @see #values(Object)
    182     */
    183    public C get(final K key) {
    184        @SuppressWarnings("unchecked") // index is a MultiMap which returns a Collection
    185        final Collection<C> coll = (Collection<C>) index.get(key);
    186        return coll == null ? null : coll.iterator().next();
    187    }
    188
    189    /**
    190     * Get all elements associated with the given key.
    191     *
    192     * @param key  key to look up
    193     * @return a collection of elements found, or null if {@code contains(key) == false}
    194     */
    195    @SuppressWarnings("unchecked") // index is a MultiMap which returns a Collection
    196    public Collection<C> values(final K key) {
    197        return (Collection<C>) index.get(key);
    198    }
    199
    200    /**
    201     * Clears the index and re-indexes the entire decorated {@link Collection}.
    202     */
    203    public void reindex() {
    204        index.clear();
    205        for (final C c : decorated()) {
    206            addToIndex(c);
    207        }
    208    }
    209
    210    @SuppressWarnings("unchecked")
    211    @Override
    212    public boolean remove(final Object object) {
    213        final boolean removed = super.remove(object);
    214        if (removed) {
    215            removeFromIndex((C) object);
    216        }
    217        return removed;
    218    }
    219
    220    /**
    221     * @since 4.4
    222     */
    223    @Override
    224    public boolean removeIf(final Predicate<? super C> filter) {
    225        if (Objects.isNull(filter)) {
    226            return false;
    227        }
    228        boolean changed = false;
    229        final Iterator<C> it = iterator();
    230        while (it.hasNext()) {
    231            if (filter.test(it.next())) {
    232                it.remove();
    233                changed = true;
    234            }
    235        }
    236        if (changed) {
    237            reindex();
    238        }
    239        return changed;
    240    }
    241
    242    @Override
    243    public boolean removeAll(final Collection<?> coll) {
    244        boolean changed = false;
    245        for (final Object o : coll) {
    246            changed |= remove(o);
    247        }
    248        return changed;
    249    }
    250
    251    @Override
    252    public boolean retainAll(final Collection<?> coll) {
    253        final boolean changed = super.retainAll(coll);
    254        if (changed) {
    255            reindex();
    256        }
    257        return changed;
    258    }
    259
    260    //-----------------------------------------------------------------------
    261
    262    /**
    263     * Provides checking for adding the index.
    264     *
    265     * @param object the object to index
    266     * @throws IllegalArgumentException if the object maps to an existing key and the index
    267     *   enforces a uniqueness constraint
    268     */
    269    private void addToIndex(final C object) {
    270        final K key = keyTransformer.transform(object);
    271        if (uniqueIndex && index.containsKey(key)) {
    272            throw new IllegalArgumentException("Duplicate key in uniquely indexed collection.");
    273        }
    274        index.put(key, object);
    275    }
    276
    277    /**
    278     * Removes an object from the index.
    279     *
    280     * @param object the object to remove
    281     */
    282    private void removeFromIndex(final C object) {
    283        index.remove(keyTransformer.transform(object));
    284    }
    285
    286}