    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.set;
    018
    019import java.util.ArrayList;
    020import java.util.Collection;
    021import java.util.HashSet;
    022import java.util.List;
    023import java.util.ListIterator;
    024import java.util.Objects;
    025import java.util.Set;
    026import java.util.function.Predicate;
    027
    028import org.apache.commons.collections4.CollectionUtils;
    029import org.apache.commons.collections4.OrderedIterator;
    030import org.apache.commons.collections4.functors.UniquePredicate;
    031import org.apache.commons.collections4.iterators.AbstractIteratorDecorator;
    032import org.apache.commons.collections4.list.UnmodifiableList;
    033
    034/**
    035 * Decorates another {@code Set} to ensure that the order of addition is
    036 * retained and used by the iterator.
    037 * <p>
    038 * If an object is added to the set for a second time, it will remain in the
    039 * original position in the iteration. The order can be observed from the set
    040 * via the iterator or toArray methods.
    041 * </p>
    042 * <p>
    043 * The ListOrderedSet also has various useful direct methods. These include many
    044 * from {@code List}, such as {@code get(int)},
    045 * {@code remove(int)} and {@code indexOf(int)}. An unmodifiable
    046 * {@code List} view of the set can be obtained via {@code asList()}.
    047 * </p>
    048 * <p>
    049 * This class cannot implement the {@code List} interface directly as
    050 * various interface methods (notably equals/hashCode) are incompatible with a
    051 * set.
    052 * </p>
    053 * <p>
    054 * This class is Serializable from Commons Collections 3.1.
    055 * </p>
    056 *
    057 * @param <E> the type of the elements in this set
    058 * @since 3.0
    059 */
    060public class ListOrderedSet<E>
    061    extends AbstractSerializableSetDecorator<E> {
    062
    063    /**
    064     * Internal iterator handle remove.
    065     */
    066    static class OrderedSetIterator<E>
    067        extends AbstractIteratorDecorator<E>
    068        implements OrderedIterator<E> {
    069
    070        /** Object we iterate on */
    071        private final Collection<E> set;
    072
    073        /** Last object retrieved */
    074        private E last;
    075
    076        private OrderedSetIterator(final ListIterator<E> iterator, final Collection<E> set) {
    077            super(iterator);
    078            this.set = set;
    079        }
    080
    081        @Override
    082        public boolean hasPrevious() {
    083            return ((ListIterator<E>) getIterator()).hasPrevious();
    084        }
    085
    086        @Override
    087        public E next() {
    088            last = getIterator().next();
    089            return last;
    090        }
    091
    092        @Override
    093        public E previous() {
    094            last = ((ListIterator<E>) getIterator()).previous();
    095            return last;
    096        }
    097
    098        @Override
    099        public void remove() {
    100            set.remove(last);
    101            getIterator().remove();
    102            last = null;
    103        }
    104    }
    105
    106    /** Serialization version */
    107    private static final long serialVersionUID = -228664372470420141L;
    108
    109    /**
    110     * Factory method to create an ordered set using the supplied list to retain order.
    111     * <p>
    112     * A {@code HashSet} is used for the set behavior.
    113     * <p>
    114     * NOTE: If the list contains duplicates, the duplicates are removed,
    115     * altering the specified list.
    116     *
    117     * @param <E> the element type
    118     * @param list the list to decorate, must not be null
    119     * @return a new ordered set
    120     * @throws NullPointerException if list is null
    121     * @since 4.0
    122     */
    123    public static <E> ListOrderedSet<E> listOrderedSet(final List<E> list) {
    124        Objects.requireNonNull(list, "list");
    125        CollectionUtils.filter(list, UniquePredicate.uniquePredicate());
    126        final Set<E> set = new HashSet<>(list);
    127
    128        return new ListOrderedSet<>(set, list);
    129    }
    130
    131    /**
    132     * Factory method to create an ordered set.
    133     * <p>
    134     * An {@code ArrayList} is used to retain order.
    135     *
    136     * @param <E> the element type
    137     * @param set the set to decorate, must not be null
    138     * @return a new ordered set
    139     * @throws NullPointerException if set is null
    140     * @since 4.0
    141     */
    142    public static <E> ListOrderedSet<E> listOrderedSet(final Set<E> set) {
    143        return new ListOrderedSet<>(set);
    144    }
    145
    146    /**
    147     * Factory method to create an ordered set specifying the list and set to use.
    148     * <p>
    149     * The list and set must both be empty.
    150     *
    151     * @param <E> the element type
    152     * @param set the set to decorate, must be empty and not null
    153     * @param list the list to decorate, must be empty and not null
    154     * @return a new ordered set
    155     * @throws NullPointerException if set or list is null
    156     * @throws IllegalArgumentException if either the set or list is not empty
    157     * @since 4.0
    158     */
    159    public static <E> ListOrderedSet<E> listOrderedSet(final Set<E> set, final List<E> list) {
    160        Objects.requireNonNull(set, "set");
    161        Objects.requireNonNull(list, "list");
    162        if (!set.isEmpty() || !list.isEmpty()) {
    163            throw new IllegalArgumentException("Set and List must be empty");
    164        }
    165        return new ListOrderedSet<>(set, list);
    166    }
    167
    168    /** Internal list to hold the sequence of objects */
    169    private final List<E> setOrder;
    170
    171    /**
    172     * Constructs a new empty {@code ListOrderedSet} using a
    173     * {@code HashSet} and an {@code ArrayList} internally.
    174     *
    175     * @since 3.1
    176     */
    177    public ListOrderedSet() {
    178        super(new HashSet<>());
    179        setOrder = new ArrayList<>();
    180    }
    181
    182    /**
    183     * Constructor that wraps (not copies).
    184     *
    185     * @param set the set to decorate, must not be null
    186     * @throws NullPointerException if set is null
    187     */
    188    protected ListOrderedSet(final Set<E> set) {
    189        super(set);
    190        setOrder = new ArrayList<>(set);
    191    }
    192
    193    /**
    194     * Constructor that wraps (not copies) the Set and specifies the list to
    195     * use.
    196     * <p>
    197     * The set and list must both be correctly initialized to the same elements.
    198     *
    199     * @param set the set to decorate, must not be null
    200     * @param list the list to decorate, must not be null
    201     * @throws NullPointerException if set or list is null
    202     */
    203    protected ListOrderedSet(final Set<E> set, final List<E> list) {
    204        super(set);
    205        setOrder = Objects.requireNonNull(list, "list");
    206    }
    207
    208    @Override
    209    public boolean add(final E object) {
    210        if (decorated().add(object)) {
    211            setOrder.add(object);
    212            return true;
    213        }
    214        return false;
    215    }
    216
    217    /**
    218     * Inserts the specified element at the specified position if it is not yet
    219     * contained in this ordered set (optional operation). Shifts the element
    220     * currently at this position and any subsequent elements to the right.
    221     *
    222     * @param index the index at which the element is to be inserted
    223     * @param object the element to be inserted
    224     * @see List#add(int, Object)
    225     */
    226    public void add(final int index, final E object) {
    227        if (!contains(object)) {
    228            decorated().add(object);
    229            setOrder.add(index, object);
    230        }
    231    }
    232
    233    @Override
    234    public boolean addAll(final Collection<? extends E> coll) {
    235        boolean result = false;
    236        for (final E e : coll) {
    237            result |= add(e);
    238        }
    239        return result;
    240    }
    241
    242    /**
    243     * Inserts all elements in the specified collection not yet contained in the
    244     * ordered set at the specified position (optional operation). Shifts the
    245     * element currently at the position and all subsequent elements to the
    246     * right.
    247     *
    248     * @param index the position to insert the elements
    249     * @param coll the collection containing the elements to be inserted
    250     * @return {@code true} if this ordered set changed as a result of the call
    251     * @see List#addAll(int, Collection)
    252     */
    253    public boolean addAll(final int index, final Collection<? extends E> coll) {
    254        boolean changed = false;
    255        // collect all elements to be added for performance reasons
    256        final List<E> toAdd = new ArrayList<>();
    257        for (final E e : coll) {
    258            if (contains(e)) {
    259                continue;
    260            }
    261            decorated().add(e);
    262            toAdd.add(e);
    263            changed = true;
    264        }
    265
    266        if (changed) {
    267            setOrder.addAll(index, toAdd);
    268        }
    269
    270        return changed;
    271    }
    272
    273    /**
    274     * Gets an unmodifiable view of the order of the Set.
    275     *
    276     * @return an unmodifiable list view
    277     */
    278    public List<E> asList() {
    279        return UnmodifiableList.unmodifiableList(setOrder);
    280    }
    281
    282    @Override
    283    public void clear() {
    284        decorated().clear();
    285        setOrder.clear();
    286    }
    287
    288    /**
    289     * Returns the element at the specified position in this ordered set.
    290     *
    291     * @param index the position of the element in the ordered {@link Set}.
    292     * @return the element at position {@code index}
    293     * @see List#get(int)
    294     */
    295    public E get(final int index) {
    296        return setOrder.get(index);
    297    }
    298
    299    /**
    300     * Returns the index of the first occurrence of the specified element in
    301     * ordered set.
    302     *
    303     * @param object the element to search for
    304     * @return the index of the first occurrence of the object, or {@code -1} if
    305     *         this ordered set does not contain this object
    306     * @see List#indexOf(Object)
    307     */
    308    public int indexOf(final Object object) {
    309        return setOrder.indexOf(object);
    310    }
    311
    312    @Override
    313    public OrderedIterator<E> iterator() {
    314        return new OrderedSetIterator<>(setOrder.listIterator(), decorated());
    315    }
    316
    317    /**
    318     * Removes the element at the specified position from the ordered set.
    319     * Shifts any subsequent elements to the left.
    320     *
    321     * @param index the index of the element to be removed
    322     * @return the element that has been remove from the ordered set
    323     * @see List#remove(int)
    324     */
    325    public E remove(final int index) {
    326        final E obj = setOrder.remove(index);
    327        remove(obj);
    328        return obj;
    329    }
    330
    331    @Override
    332    public boolean remove(final Object object) {
    333        final boolean result = decorated().remove(object);
    334        if (result) {
    335            setOrder.remove(object);
    336        }
    337        return result;
    338    }
    339
    340    @Override
    341    public boolean removeAll(final Collection<?> coll) {
    342        boolean result = false;
    343        for (final Object name : coll) {
    344            result |= remove(name);
    345        }
    346        return result;
    347    }
    348
    349    /**
    350     * @since 4.4
    351     */
    352    @Override
    353    public boolean removeIf(final Predicate<? super E> filter) {
    354        if (Objects.isNull(filter)) {
    355            return false;
    356        }
    357        final boolean result = decorated().removeIf(filter);
    358        if (result) {
    359            setOrder.removeIf(filter);
    360        }
    361        return result;
    362    }
    363
    364    /**
    365     * {@inheritDoc}
    366     * <p>
    367     * This implementation iterates over the elements of this set, checking
    368     * each element in turn to see if it's contained in {@code coll}.
    369     * If it's not contained, it's removed from this set. As a consequence,
    370     * it is advised to use a collection type for {@code coll} that provides
    371     * a fast (e.g. O(1)) implementation of {@link Collection#contains(Object)}.
    372     */
    373    @Override
    374    public boolean retainAll(final Collection<?> coll) {
    375        final boolean result = decorated().retainAll(coll);
    376        if (!result) {
    377            return false;
    378        }
    379        if (decorated().isEmpty()) {
    380            setOrder.clear();
    381        } else {
    382            setOrder.removeIf(e -> !decorated().contains(e));
    383        }
    384        return result;
    385    }
    386
    387    @Override
    388    public Object[] toArray() {
    389        return setOrder.toArray();
    390    }
    391
    392    @Override
    393    public <T> T[] toArray(final T[] a) {
    394        return setOrder.toArray(a);
    395    }
    396
    397    /**
    398     * Uses the underlying List's toString so that order is achieved. This means
    399     * that the decorated Set's toString is not used, so any custom toStrings
    400     * will be ignored.
    401     *
    402     * @return a string representation of the ordered set
    403     */
    404    // Fortunately List.toString and Set.toString look the same
    405    @Override
    406    public String toString() {
    407        return setOrder.toString();
    408    }
    409
    410}