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/*
* Copyright (C) 2007 Google Inc.
*
* Licensed 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 com.google.common.collect;
import com.google.common.base.Nullable;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.Set;
/**
* Implementation of {@code Multimap} that does not allow duplicate key-value
* entries and that returns collections whose iterators follow the ordering in
* which the data was added to the multimap.
*
* The collections returned by {@code keySet}, {@code keys}, and {@code
* asMap} iterate through the keys in the order they were first added to the
* multimap. Similarly, {@code get}, {@code removeAll}, and {@code
* replaceValues} return collections that iterate through the values in the
* order they were added. The collections generated by {@code entries} and
* {@code values} iterate across the key-value mappings in the order they were
* added to the multimap.
*
*
The iteration ordering of the collections generated by {@code keySet},
* {@code keys}, and {@code asMap} has a few subtleties. As long as the set of
* keys remains unchanged, adding or removing mappings does not affect the key
* iteration order. However, if you remove all values associated with a key and
* then add the key back to the multimap, that key will come last in the key
* iteration order.
*
*
The multimap does not store duplicate key-value pairs. Adding a new
* key-value pair equal to an existing key-value pair has no effect.
*
*
Keys and values may be null. All optional multimap methods are supported,
* and all returned views are modifiable.
*
*
This class is not threadsafe when any concurrent operations update the
* multimap. Concurrent read operations will work correctly. To allow concurrent
* update operations, wrap your multimap with a call to {@link
* Multimaps#synchronizedSetMultimap}.
*
* @author Jared Levy
*/
public final class LinkedHashMultimap extends StandardSetMultimap {
/**
* Map entries with an iteration order corresponding to the order in which the
* key-value pairs were added to the multimap.
*/
private transient Collection> linkedEntries;
/** Constructs an empty {@code LinkedHashMultimap}. */
public LinkedHashMultimap() {
super(new LinkedHashMap>());
linkedEntries = Sets.newLinkedHashSet();
}
/**
* Constructs a {@code LinkedHashMultimap} with the same mappings as the
* specified {@code Multimap}. If a key-value mapping appears multiple times
* in the input multimap, it only appears once in the constructed multimap.
* The new multimap has the same {@link Multimap#entries()} iteration order as
* the input multimap, except for excluding duplicate mappings.
*/
public LinkedHashMultimap(Multimap multimap) {
super(new LinkedHashMap>(
Maps.capacity(multimap.keySet().size())));
linkedEntries
= new LinkedHashSet>(Maps.capacity(multimap.size()));
putAll(multimap);
}
/**
* {@inheritDoc}
*
* Creates an empty {@code LinkedHashSet} for a collection of values for
* one key.
*
* @return a new {@code LinkedHashSet} containing a collection of values for
* one key
*/
@Override Set createCollection() {
return new LinkedHashSet();
}
/**
* {@inheritDoc}
*
* Creates a decorated {@code LinkedHashSet} that also keeps track of the
* order in which key-value pairs are added to the multimap.
*
* @param key key to associate with values in the collection
* @return a new decorated {@code LinkedHashSet} containing a collection of
* values for one key
*/
@Override Collection createCollection(@Nullable K key) {
return new SetDecorator(key, createCollection());
}
private class SetDecorator extends ForwardingSet {
final Set delegate;
final K key;
SetDecorator(@Nullable K key, Set delegate) {
this.delegate = delegate;
this.key = key;
}
@Override protected Set delegate() {
return delegate;
}
Map.Entry createEntry(@Nullable E value) {
return Maps.immutableEntry(key, value);
}
Collection> createEntries(Collection values) {
// converts a collection of values into a list of key/value map entries
Collection> entries
= Lists.newArrayListWithExpectedSize(values.size());
for (E value : values) {
entries.add(createEntry(value));
}
return entries;
}
@Override public boolean add(@Nullable V value) {
boolean changed = delegate.add(value);
if (changed) {
linkedEntries.add(createEntry(value));
}
return changed;
}
@Override public boolean addAll(Collection values) {
boolean changed = delegate.addAll(values);
if (changed) {
linkedEntries.addAll(createEntries(delegate()));
}
return changed;
}
@Override public void clear() {
linkedEntries.removeAll(createEntries(delegate()));
delegate.clear();
}
@Override public Iterator iterator() {
final Iterator delegateIterator = delegate.iterator();
return new Iterator() {
V value;
public boolean hasNext() {
return delegateIterator.hasNext();
}
public V next() {
value = delegateIterator.next();
return value;
}
public void remove() {
delegateIterator.remove();
linkedEntries.remove(createEntry(value));
}
};
}
@Override public boolean remove(@Nullable Object value) {
boolean changed = delegate.remove(value);
if (changed) {
/*
* linkedEntries.remove() will return false when this method is called
* by entries().iterator().remove()
*/
linkedEntries.remove(createEntry(value));
}
return changed;
}
@Override public boolean removeAll(Collection values) {
boolean changed = delegate.removeAll(values);
if (changed) {
linkedEntries.removeAll(createEntries(values));
}
return changed;
}
@Override public boolean retainAll(Collection values) {
/*
* Calling linkedEntries.retainAll() would incorrectly remove values
* with other keys.
*/
boolean changed = false;
Iterator iterator = delegate.iterator();
while (iterator.hasNext()) {
V value = iterator.next();
if (!values.contains(value)) {
iterator.remove();
linkedEntries.remove(Maps.immutableEntry(key, value));
changed = true;
}
}
return changed;
}
}
/**
* {@inheritDoc}
*
* Generates an iterator across map entries that follows the ordering in
* which the key-value pairs were added to the multimap.
*
* @return a key-value iterator with the correct ordering
*/
@Override Iterator> createEntryIterator() {
final Iterator> delegateIterator = linkedEntries.iterator();
return new Iterator>() {
Map.Entry entry;
public boolean hasNext() {
return delegateIterator.hasNext();
}
public Map.Entry next() {
entry = delegateIterator.next();
return entry;
}
public void remove() {
// Remove from iterator first to keep iterator valid.
delegateIterator.remove();
LinkedHashMultimap.this.remove(entry.getKey(), entry.getValue());
}
};
}
/**
* {@inheritDoc}
*
* If {@code values} is not empty and the multimap already contains a
* mapping for {@code key}, the {@code keySet()} ordering is unchanged.
* However, the provided values always come last in the {@link #entries()} and
* {@link #values()} iteration orderings.
*/
@Override public Set replaceValues(
@Nullable K key, Iterable values) {
return super.replaceValues(key, values);
}
/**
* Returns a set of all key-value pairs. Changes to the returned set will
* update the underlying multimap, and vice versa. The entries set does not
* support the {@code add} or {@code addAll} operations.
*
* The iterator generated by the returned set traverses the entries in the
* order they were added to the multimap.
*
*
Each entry is an immutable snapshot of a key-value mapping in the
* multimap, taken at the time the entry is returned by a method call to the
* collection or its iterator.
*/
@Override public Set> entries() {
return super.entries();
}
/**
* Returns a collection of all values in the multimap. Changes to the returned
* collection will update the underlying multimap, and vice versa.
*
* The iterator generated by the returned collection traverses the values
* in the order they were added to the multimap.
*/
@Override public Collection values() {
return super.values();
}
// Unfortunately, the entries() ordering does not determine the key ordering;
// see the example in the LinkedListMultimap class Javadoc.
/**
* @serialData the number of distinct keys, and then for each distinct key:
* the first key, the number of values for that key, and the key's values,
* followed by successive keys and values from the entries() ordering
*/
private void writeObject(ObjectOutputStream stream) throws IOException {
stream.defaultWriteObject();
Serialization.writeMultimap(this, stream);
for (Map.Entry entry : linkedEntries) {
stream.writeObject(entry.getKey());
stream.writeObject(entry.getValue());
}
}
private void readObject(ObjectInputStream stream)
throws IOException, ClassNotFoundException {
stream.defaultReadObject();
setMap(new LinkedHashMap>());
linkedEntries = Sets.newLinkedHashSet();
Serialization.populateMultimap(this, stream);
linkedEntries.clear(); // will clear and repopulate entries
for (int i = 0; i < size(); i++) {
@SuppressWarnings("unchecked") // reading data stored by writeObject
K key = (K) stream.readObject();
@SuppressWarnings("unchecked") // reading data stored by writeObject
V value = (V) stream.readObject();
linkedEntries.add(Maps.immutableEntry(key, value));
}
}
private static final long serialVersionUID = 0;
}