/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.collections4.multimap;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.AbstractCollection;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import org.apache.commons.collections4.CollectionUtils;
import org.apache.commons.collections4.IteratorUtils;
import org.apache.commons.collections4.MapIterator;
import org.apache.commons.collections4.MultiSet;
import org.apache.commons.collections4.MultiValuedMap;
import org.apache.commons.collections4.Transformer;
import org.apache.commons.collections4.iterators.AbstractIteratorDecorator;
import org.apache.commons.collections4.iterators.EmptyMapIterator;
import org.apache.commons.collections4.iterators.IteratorChain;
import org.apache.commons.collections4.iterators.LazyIteratorChain;
import org.apache.commons.collections4.iterators.TransformIterator;
import org.apache.commons.collections4.keyvalue.AbstractMapEntry;
import org.apache.commons.collections4.keyvalue.UnmodifiableMapEntry;
import org.apache.commons.collections4.multiset.AbstractMultiSet;
import org.apache.commons.collections4.multiset.UnmodifiableMultiSet;

Abstract implementation of the MultiValuedMap interface to simplify the creation of subclass implementations. 

Subclasses specify a Map implementation to use as the internal storage.

Type parameters:
<K> – the type of the keys in this map
<V> – the type of the values in this map
Since:
4.1/**
 * Abstract implementation of the {@link MultiValuedMap} interface to simplify
 * the creation of subclass implementations.
 * <p>
 * Subclasses specify a Map implementation to use as the internal storage.
 * </p>
 *
 * @param <K> the type of the keys in this map
 * @param <V> the type of the values in this map
 * @since 4.1
 */
public abstract class AbstractMultiValuedMap<K, V> implements MultiValuedMap<K, V> {

    
The values view /** The values view */
    private transient Collection<V> valuesView;

    
The EntryValues view /** The EntryValues view */
    private transient EntryValues entryValuesView;

    
The KeyMultiSet view /** The KeyMultiSet view */
    private transient MultiSet<K> keysMultiSetView;

    
The AsMap view /** The AsMap view */
    private transient AsMap asMapView;

    
The map used to store the data /** The map used to store the data */
    private transient Map<K, Collection<V>> map;

    
Constructor needed for subclass serialisation.
/**
     * Constructor needed for subclass serialisation.
     */
    protected AbstractMultiValuedMap() {
        super();
    }

    
Constructor that wraps (not copies).
Params:
map –  the map to wrap, must not be null
Throws:
NullPointerException – if the map is null/**
     * Constructor that wraps (not copies).
     *
     * @param map  the map to wrap, must not be null
     * @throws NullPointerException if the map is null
     */
    @SuppressWarnings("unchecked")
    protected AbstractMultiValuedMap(final Map<K, ? extends Collection<V>> map) {
        if (map == null) {
            throw new NullPointerException("Map must not be null.");
        }
        this.map = (Map<K, Collection<V>>) map;
    }

    // -----------------------------------------------------------------------
    
Gets the map being wrapped.
Returns:
the wrapped map/**
     * Gets the map being wrapped.
     *
     * @return the wrapped map
     */
    protected Map<K, ? extends Collection<V>> getMap() {
        return map;
    }

    
Sets the map being wrapped.

NOTE: this method should only be used during deserialization
Params:
map – the map to wrap/**
     * Sets the map being wrapped.
     * <p>
     * <b>NOTE:</b> this method should only be used during deserialization
     *
     * @param map the map to wrap
     */
    @SuppressWarnings("unchecked")
    protected void setMap(final Map<K, ? extends Collection<V>> map) {
        this.map = (Map<K, Collection<V>>) map;
    }

    protected abstract Collection<V> createCollection();

    // -----------------------------------------------------------------------
    @Override
    public boolean containsKey(final Object key) {
        return getMap().containsKey(key);
    }

    @Override
    public boolean containsValue(final Object value) {
        return values().contains(value);
    }

    @Override
    public boolean containsMapping(final Object key, final Object value) {
        final Collection<V> coll = getMap().get(key);
        return coll != null && coll.contains(value);
    }

    @Override
    public Collection<Entry<K, V>> entries() {
        return entryValuesView != null ? entryValuesView : (entryValuesView = new EntryValues());
    }

    
Gets the collection of values associated with the specified key. This
would return an empty collection in case the mapping is not present
Params:
key – the key to retrieve
Returns:
the Collection of values, will return an empty Collection for no mapping/**
     * Gets the collection of values associated with the specified key. This
     * would return an empty collection in case the mapping is not present
     *
     * @param key the key to retrieve
     * @return the {@code Collection} of values, will return an empty {@code Collection} for no mapping
     */
    @Override
    public Collection<V> get(final K key) {
        return wrappedCollection(key);
    }

    Collection<V> wrappedCollection(final K key) {
        return new WrappedCollection(key);
    }

    
Removes all values associated with the specified key.

A subsequent get(Object) would return an empty collection.
Params:
key –  the key to remove values from
Returns:
the Collection of values removed, will return an
  empty, unmodifiable collection for no mapping found/**
     * Removes all values associated with the specified key.
     * <p>
     * A subsequent <code>get(Object)</code> would return an empty collection.
     *
     * @param key  the key to remove values from
     * @return the <code>Collection</code> of values removed, will return an
     *   empty, unmodifiable collection for no mapping found
     */
    @Override
    public Collection<V> remove(final Object key) {
        return CollectionUtils.emptyIfNull(getMap().remove(key));
    }

    
Removes a specific key/value mapping from the multi-valued map.

The value is removed from the collection mapped to the specified key.
Other values attached to that key are unaffected.
 If the last value for a key is removed, an empty collection would be returned from a subsequent get(Object). 
Params:
key – the key to remove from
value – the value to remove
Returns:
true if the mapping was removed, false otherwise/**
     * Removes a specific key/value mapping from the multi-valued map.
     * <p>
     * The value is removed from the collection mapped to the specified key.
     * Other values attached to that key are unaffected.
     * <p>
     * If the last value for a key is removed, an empty collection would be
     * returned from a subsequent {@link #get(Object)}.
     *
     * @param key the key to remove from
     * @param value the value to remove
     * @return true if the mapping was removed, false otherwise
     */
    @Override
    public boolean removeMapping(final Object key, final Object value) {
        final Collection<V> coll = getMap().get(key);
        if (coll == null) {
            return false;
        }
        final boolean changed = coll.remove(value);
        if (coll.isEmpty()) {
            getMap().remove(key);
        }
        return changed;
    }

    @Override
    public boolean isEmpty() {
        return getMap().isEmpty();
    }

    @Override
    public Set<K> keySet() {
        return getMap().keySet();
    }

    
{@inheritDoc}

This implementation does not cache the total size
of the multi-valued map, but rather calculates it by iterating
over the entries of the underlying map.
/**
     * {@inheritDoc}
     * <p>
     * This implementation does <b>not</b> cache the total size
     * of the multi-valued map, but rather calculates it by iterating
     * over the entries of the underlying map.
     */
    @Override
    public int size() {
        // the total size should be cached to improve performance
        // but this requires that all modifications of the multimap
        // (including the wrapped collections and entry/value
        // collections) are tracked.
        int size = 0;
        for (final Collection<V> col : getMap().values()) {
            size += col.size();
        }
        return size;
    }

    
Gets a collection containing all the values in the map.

Returns a collection containing all the values from all keys.
Returns:
a collection view of the values contained in this map/**
     * Gets a collection containing all the values in the map.
     * <p>
     * Returns a collection containing all the values from all keys.
     *
     * @return a collection view of the values contained in this map
     */
    @Override
    public Collection<V> values() {
        final Collection<V> vs = valuesView;
        return vs != null ? vs : (valuesView = new Values());
    }

    @Override
    public void clear() {
        getMap().clear();
    }

    
Adds the value to the collection associated with the specified key.

Unlike a normal Map the previous value is not replaced.
Instead the new value is added to the collection stored against the key.
Params:
key – the key to store against
value – the value to add to the collection at the key
Returns:
the value added if the map changed and null if the map did not change/**
     * Adds the value to the collection associated with the specified key.
     * <p>
     * Unlike a normal <code>Map</code> the previous value is not replaced.
     * Instead the new value is added to the collection stored against the key.
     *
     * @param key the key to store against
     * @param value the value to add to the collection at the key
     * @return the value added if the map changed and null if the map did not change
     */
    @Override
    public boolean put(final K key, final V value) {
        Collection<V> coll = getMap().get(key);
        if (coll == null) {
            coll = createCollection();
            if (coll.add(value)) {
                map.put(key, coll);
                return true;
            }
            return false;
        }
        return coll.add(value);
    }

    
Copies all of the mappings from the specified map to this map. The effect of this call is equivalent to that of calling 
put(k, v) on this map once for each mapping from key k to value v in the specified map. The behavior of this operation is undefined if the specified map is modified while the operation is in progress. 
Params:
map – mappings to be stored in this map, may not be null
Throws:
NullPointerException – if map is null
Returns:
true if the map changed as a result of this operation/**
     * Copies all of the mappings from the specified map to this map. The effect
     * of this call is equivalent to that of calling {@link #put(Object,Object)
     * put(k, v)} on this map once for each mapping from key {@code k} to value
     * {@code v} in the specified map. The behavior of this operation is
     * undefined if the specified map is modified while the operation is in
     * progress.
     *
     * @param map mappings to be stored in this map, may not be null
     * @return true if the map changed as a result of this operation
     * @throws NullPointerException if map is null
     */
    @Override
    public boolean putAll(final Map<? extends K, ? extends V> map) {
        if (map == null) {
            throw new NullPointerException("Map must not be null.");
        }
        boolean changed = false;
        for (final Map.Entry<? extends K, ? extends V> entry : map.entrySet()) {
            changed |= put(entry.getKey(), entry.getValue());
        }
        return changed;
    }

    
Copies all of the mappings from the specified MultiValuedMap to this map. The effect of this call is equivalent to that of calling put(k, v) on this map once for each mapping from key k to value v in the specified map. The behavior of this operation is undefined if the specified map is modified while the operation is in progress. 
Params:
map – mappings to be stored in this map, may not be null
Throws:
NullPointerException – if map is null
Returns:
true if the map changed as a result of this operation/**
     * Copies all of the mappings from the specified MultiValuedMap to this map.
     * The effect of this call is equivalent to that of calling
     * {@link #put(Object,Object) put(k, v)} on this map once for each mapping
     * from key {@code k} to value {@code v} in the specified map. The
     * behavior of this operation is undefined if the specified map is modified
     * while the operation is in progress.
     *
     * @param map mappings to be stored in this map, may not be null
     * @return true if the map changed as a result of this operation
     * @throws NullPointerException if map is null
     */
    @Override
    public boolean putAll(final MultiValuedMap<? extends K, ? extends V> map) {
        if (map == null) {
            throw new NullPointerException("Map must not be null.");
        }
        boolean changed = false;
        for (final Map.Entry<? extends K, ? extends V> entry : map.entries()) {
            changed |= put(entry.getKey(), entry.getValue());
        }
        return changed;
    }

    
Returns a MultiSet view of the key mapping contained in this map. 
 Returns a MultiSet of keys with its values count as the count of the MultiSet. This multiset is backed by the map, so any changes in the map is reflected here. Any method which modifies this multiset like add, remove, Iterator.remove() etc throws UnsupportedOperationException. 
Returns:
a bag view of the key mapping contained in this map/**
     * Returns a {@link MultiSet} view of the key mapping contained in this map.
     * <p>
     * Returns a MultiSet of keys with its values count as the count of the MultiSet.
     * This multiset is backed by the map, so any changes in the map is reflected here.
     * Any method which modifies this multiset like {@code add}, {@code remove},
     * {@link Iterator#remove()} etc throws {@code UnsupportedOperationException}.
     *
     * @return a bag view of the key mapping contained in this map
     */
    @Override
    public MultiSet<K> keys() {
        if (keysMultiSetView == null) {
            keysMultiSetView = UnmodifiableMultiSet.unmodifiableMultiSet(new KeysMultiSet());
        }
        return keysMultiSetView;
    }

    @Override
    public Map<K, Collection<V>> asMap() {
        return asMapView != null ? asMapView : (asMapView = new AsMap(map));
    }

    
Adds Iterable values to the collection associated with the specified key.
Params:
key – the key to store against
values – the values to add to the collection at the key, may not be null
Throws:
NullPointerException – if values is null
Returns:
true if this map changed/**
     * Adds Iterable values to the collection associated with the specified key.
     *
     * @param key the key to store against
     * @param values the values to add to the collection at the key, may not be null
     * @return true if this map changed
     * @throws NullPointerException if values is null
     */
    @Override
    public boolean putAll(final K key, final Iterable<? extends V> values) {
        if (values == null) {
            throw new NullPointerException("Values must not be null.");
        }

        if (values instanceof Collection<?>) {
            final Collection<? extends V> valueCollection = (Collection<? extends V>) values;
            return !valueCollection.isEmpty() && get(key).addAll(valueCollection);
        }
        final Iterator<? extends V> it = values.iterator();
        return it.hasNext() && CollectionUtils.addAll(get(key), it);
    }

    @Override
    public MapIterator<K, V> mapIterator() {
        if (size() == 0) {
            return EmptyMapIterator.emptyMapIterator();
        }
        return new MultiValuedMapIterator();
    }

    @Override
    public boolean equals(final Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj instanceof MultiValuedMap) {
            return asMap().equals(((MultiValuedMap<?, ?>) obj).asMap());
        }
        return false;
    }

    @Override
    public int hashCode() {
        return getMap().hashCode();
    }

    @Override
    public String toString() {
        return getMap().toString();
    }

    // -----------------------------------------------------------------------

    
Wrapped collection to handle add and remove on the collection returned
by get(object).

Currently, the wrapped collection is not cached and has to be retrieved
from the underlying map. This is safe, but not very efficient and
should be improved in subsequent releases. For this purpose, the
scope of this collection is set to package private to simplify later
refactoring.
/**
     * Wrapped collection to handle add and remove on the collection returned
     * by get(object).
     * <p>
     * Currently, the wrapped collection is not cached and has to be retrieved
     * from the underlying map. This is safe, but not very efficient and
     * should be improved in subsequent releases. For this purpose, the
     * scope of this collection is set to package private to simplify later
     * refactoring.
     */
    class WrappedCollection implements Collection<V> {

        protected final K key;

        public WrappedCollection(final K key) {
            this.key = key;
        }

        protected Collection<V> getMapping() {
            return getMap().get(key);
        }

        @Override
        public boolean add(final V value) {
            Collection<V> coll = getMapping();
            if (coll == null) {
                coll = createCollection();
                AbstractMultiValuedMap.this.map.put(key, coll);
            }
            return coll.add(value);
        }

        @Override
        public boolean addAll(final Collection<? extends V> other) {
            Collection<V> coll = getMapping();
            if (coll == null) {
                coll = createCollection();
                AbstractMultiValuedMap.this.map.put(key, coll);
            }
            return coll.addAll(other);
        }

        @Override
        public void clear() {
            final Collection<V> coll = getMapping();
            if (coll != null) {
                coll.clear();
                AbstractMultiValuedMap.this.remove(key);
            }
        }

        @Override
        public Iterator<V> iterator() {
            final Collection<V> coll = getMapping();
            if (coll == null) {
                return IteratorUtils.EMPTY_ITERATOR;
            }
            return new ValuesIterator(key);
        }

        @Override
        public int size() {
            final Collection<V> coll = getMapping();
            return coll == null ? 0 : coll.size();
        }

        @Override
        public boolean contains(final Object obj) {
            final Collection<V> coll = getMapping();
            return coll != null && coll.contains(obj);
        }

        @Override
        public boolean containsAll(final Collection<?> other) {
            final Collection<V> coll = getMapping();
            return coll != null && coll.containsAll(other);
        }

        @Override
        public boolean isEmpty() {
            final Collection<V> coll = getMapping();
            return coll == null || coll.isEmpty();
        }

        @Override
        public boolean remove(final Object item) {
            final Collection<V> coll = getMapping();
            if (coll == null) {
                return false;
            }

            final boolean result = coll.remove(item);
            if (coll.isEmpty()) {
                AbstractMultiValuedMap.this.remove(key);
            }
            return result;
        }

        @Override
        public boolean removeAll(final Collection<?> c) {
            final Collection<V> coll = getMapping();
            if (coll == null) {
                return false;
            }

            final boolean result = coll.removeAll(c);
            if (coll.isEmpty()) {
                AbstractMultiValuedMap.this.remove(key);
            }
            return result;
        }

        @Override
        public boolean retainAll(final Collection<?> c) {
            final Collection<V> coll = getMapping();
            if (coll == null) {
                return false;
            }

            final boolean result = coll.retainAll(c);
            if (coll.isEmpty()) {
                AbstractMultiValuedMap.this.remove(key);
            }
            return result;
        }

        @Override
        public Object[] toArray() {
            final Collection<V> coll = getMapping();
            if (coll == null) {
                return CollectionUtils.EMPTY_COLLECTION.toArray();
            }
            return coll.toArray();
        }

        @Override
        @SuppressWarnings("unchecked")
        public <T> T[] toArray(final T[] a) {
            final Collection<V> coll = getMapping();
            if (coll == null) {
                return (T[]) CollectionUtils.EMPTY_COLLECTION.toArray(a);
            }
            return coll.toArray(a);
        }

        @Override
        public String toString() {
            final Collection<V> coll = getMapping();
            if (coll == null) {
                return CollectionUtils.EMPTY_COLLECTION.toString();
            }
            return coll.toString();
        }

    }

    
Inner class that provides a MultiSet keys view.
/**
     * Inner class that provides a MultiSet<K> keys view.
     */
    private class KeysMultiSet extends AbstractMultiSet<K> {

        @Override
        public boolean contains(final Object o) {
            return getMap().containsKey(o);
        }

        @Override
        public boolean isEmpty() {
            return getMap().isEmpty();
        }

        @Override
        public int size() {
            return AbstractMultiValuedMap.this.size();
        }

        @Override
        protected int uniqueElements() {
            return getMap().size();
        }

        @Override
        public int getCount(final Object object) {
            int count = 0;
            final Collection<V> col = AbstractMultiValuedMap.this.getMap().get(object);
            if (col != null) {
                count = col.size();
            }
            return count;
        }

        @Override
        protected Iterator<MultiSet.Entry<K>> createEntrySetIterator() {
            final MapEntryTransformer transformer = new MapEntryTransformer();
            return IteratorUtils.transformedIterator(map.entrySet().iterator(), transformer);
        }

        private final class MapEntryTransformer
            implements Transformer<Map.Entry<K, Collection<V>>, MultiSet.Entry<K>> {
            @Override
            public MultiSet.Entry<K> transform(final Map.Entry<K, Collection<V>> mapEntry) {
                return new AbstractMultiSet.AbstractEntry<K>() {
                    @Override
                    public K getElement() {
                        return mapEntry.getKey();
                    }

                    @Override
                    public int getCount() {
                        return mapEntry.getValue().size();
                    }
                };
            }
        }
    }

    
Inner class that provides the Entry view
/**
     * Inner class that provides the Entry<K, V> view
     */
    private class EntryValues extends AbstractCollection<Entry<K, V>> {

        @Override
        public Iterator<Entry<K, V>> iterator() {
            return new LazyIteratorChain<Entry<K, V>>() {

                final Collection<K> keysCol = new ArrayList<>(getMap().keySet());
                final Iterator<K> keyIterator = keysCol.iterator();

                @Override
                protected Iterator<? extends Entry<K, V>> nextIterator(final int count) {
                    if (!keyIterator.hasNext()) {
                        return null;
                    }
                    final K key = keyIterator.next();
                    final Transformer<V, Entry<K, V>> entryTransformer = new Transformer<V, Entry<K, V>>() {

                        @Override
                        public Entry<K, V> transform(final V input) {
                            return new MultiValuedMapEntry(key, input);
                        }

                    };
                    return new TransformIterator<>(new ValuesIterator(key), entryTransformer);
                }
            };
        }

        @Override
        public int size() {
            return AbstractMultiValuedMap.this.size();
        }

    }

    
Inner class for MultiValuedMap Entries.
/**
     * Inner class for MultiValuedMap Entries.
     */
    private class MultiValuedMapEntry extends AbstractMapEntry<K, V> {

        public MultiValuedMapEntry(final K key, final V value) {
            super(key, value);
        }

        @Override
        public V setValue(final V value) {
            throw new UnsupportedOperationException();
        }

    }

    
Inner class for MapIterator.
/**
     * Inner class for MapIterator.
     */
    private class MultiValuedMapIterator implements MapIterator<K, V> {

        private final Iterator<Entry<K, V>> it;

        private Entry<K, V> current = null;

        public MultiValuedMapIterator() {
            this.it = AbstractMultiValuedMap.this.entries().iterator();
        }

        @Override
        public boolean hasNext() {
            return it.hasNext();
        }

        @Override
        public K next() {
            current = it.next();
            return current.getKey();
        }

        @Override
        public K getKey() {
            if (current == null) {
                throw new IllegalStateException();
            }
            return current.getKey();
        }

        @Override
        public V getValue() {
            if (current == null) {
                throw new IllegalStateException();
            }
            return current.getValue();
        }

        @Override
        public void remove() {
            it.remove();
        }

        @Override
        public V setValue(final V value) {
            if (current == null) {
                throw new IllegalStateException();
            }
            return current.setValue(value);
        }

    }

    
Inner class that provides the values view.
/**
     * Inner class that provides the values view.
     */
    private class Values extends AbstractCollection<V> {
        @Override
        public Iterator<V> iterator() {
            final IteratorChain<V> chain = new IteratorChain<>();
            for (final K k : keySet()) {
                chain.addIterator(new ValuesIterator(k));
            }
            return chain;
        }

        @Override
        public int size() {
            return AbstractMultiValuedMap.this.size();
        }

        @Override
        public void clear() {
            AbstractMultiValuedMap.this.clear();
        }
    }

    
Inner class that provides the values iterator.
/**
     * Inner class that provides the values iterator.
     */
    private class ValuesIterator implements Iterator<V> {
        private final Object key;
        private final Collection<V> values;
        private final Iterator<V> iterator;

        public ValuesIterator(final Object key) {
            this.key = key;
            this.values = getMap().get(key);
            this.iterator = values.iterator();
        }

        @Override
        public void remove() {
            iterator.remove();
            if (values.isEmpty()) {
                AbstractMultiValuedMap.this.remove(key);
            }
        }

        @Override
        public boolean hasNext() {
            return iterator.hasNext();
        }

        @Override
        public V next() {
            return iterator.next();
        }
    }

    
Inner class that provides the AsMap view.
/**
     * Inner class that provides the AsMap view.
     */
    private class AsMap extends AbstractMap<K, Collection<V>> {
        final transient Map<K, Collection<V>> decoratedMap;

        AsMap(final Map<K, Collection<V>> map) {
          this.decoratedMap = map;
        }

        @Override
        public Set<Map.Entry<K, Collection<V>>> entrySet() {
          return new AsMapEntrySet();
        }

        @Override
        public boolean containsKey(final Object key) {
            return decoratedMap.containsKey(key);
        }

        @Override
        public Collection<V> get(final Object key) {
          final Collection<V> collection = decoratedMap.get(key);
          if (collection == null) {
            return null;
          }
          @SuppressWarnings("unchecked")
        final
          K k = (K) key;
          return wrappedCollection(k);
        }

        @Override
        public Set<K> keySet() {
          return AbstractMultiValuedMap.this.keySet();
        }

        @Override
        public int size() {
          return decoratedMap.size();
        }

        @Override
        public Collection<V> remove(final Object key) {
          final Collection<V> collection = decoratedMap.remove(key);
          if (collection == null) {
            return null;
          }

          final Collection<V> output = createCollection();
          output.addAll(collection);
          collection.clear();
          return output;
        }

        @Override
        public boolean equals(final Object object) {
          return this == object || decoratedMap.equals(object);
        }

        @Override
        public int hashCode() {
          return decoratedMap.hashCode();
        }

        @Override
        public String toString() {
          return decoratedMap.toString();
        }

        @Override
        public void clear() {
            AbstractMultiValuedMap.this.clear();
        }

        class AsMapEntrySet extends AbstractSet<Map.Entry<K, Collection<V>>> {

            @Override
            public Iterator<Map.Entry<K, Collection<V>>> iterator() {
                return new AsMapEntrySetIterator(decoratedMap.entrySet().iterator());
            }

            @Override
            public int size() {
              return AsMap.this.size();
            }

            @Override
            public void clear() {
                AsMap.this.clear();
            }

            @Override
            public boolean contains(final Object o) {
                return decoratedMap.entrySet().contains(o);
            }

            @Override
            public boolean remove(final Object o) {
                if (!contains(o)) {
                    return false;
                }
                final Map.Entry<?, ?> entry = (Map.Entry<?, ?>) o;
                AbstractMultiValuedMap.this.remove(entry.getKey());
                return true;
            }
        }

        
EntrySet iterator for the asMap view.
/**
         * EntrySet iterator for the asMap view.
         */
        class AsMapEntrySetIterator extends AbstractIteratorDecorator<Map.Entry<K, Collection<V>>> {

            AsMapEntrySetIterator(final Iterator<Map.Entry<K, Collection<V>>> iterator) {
                super(iterator);
            }

            @Override
            public Map.Entry<K, Collection<V>> next() {
                final Map.Entry<K, Collection<V>> entry = super.next();
                final K key = entry.getKey();
                return new UnmodifiableMapEntry<>(key, wrappedCollection(key));
            }
        }
    }

    //-----------------------------------------------------------------------
    
Write the map out using a custom routine.
Params:
out – the output stream
Throws:
IOException – any of the usual I/O related exceptions/**
     * Write the map out using a custom routine.
     * @param out the output stream
     * @throws IOException any of the usual I/O related exceptions
     */
    protected void doWriteObject(final ObjectOutputStream out) throws IOException {
        out.writeInt(map.size());
        for (final Map.Entry<K, Collection<V>> entry : map.entrySet()) {
            out.writeObject(entry.getKey());
            out.writeInt(entry.getValue().size());
            for (final V value : entry.getValue()) {
                out.writeObject(value);
            }
        }
    }

    
Read the map in using a custom routine.
Params:
in – the input stream
Throws:
IOException – any of the usual I/O related exceptions
ClassNotFoundException – if the stream contains an object which class can not be loaded
ClassCastException – if the stream does not contain the correct objects/**
     * Read the map in using a custom routine.
     * @param in the input stream
     * @throws IOException any of the usual I/O related exceptions
     * @throws ClassNotFoundException if the stream contains an object which class can not be loaded
     * @throws ClassCastException if the stream does not contain the correct objects
     */
    protected void doReadObject(final ObjectInputStream in)
            throws IOException, ClassNotFoundException {
        final int entrySize = in.readInt();
        for (int i = 0; i < entrySize; i++) {
            @SuppressWarnings("unchecked") // This will fail at runtime if the stream is incorrect
            final K key = (K) in.readObject();
            final Collection<V> values = get(key);
            final int valueSize = in.readInt();
            for (int j = 0; j < valueSize; j++) {
                @SuppressWarnings("unchecked") // see above
                final
                V value = (V) in.readObject();
                values.add(value);
            }
        }
    }

}