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