org.apache.commons.collections4.collection.IndexedCollection Maven / Gradle / Ivy
/*
* 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.collection;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Objects;
import java.util.function.Predicate;
import org.apache.commons.collections4.MultiMap;
import org.apache.commons.collections4.Transformer;
import org.apache.commons.collections4.map.MultiValueMap;
/**
* An IndexedCollection is a Map-like view onto a Collection. It accepts a
* keyTransformer to define how the keys are converted from the values.
*
* Modifications made to this decorator modify the index as well as the
* decorated {@link Collection}. However, modifications to the underlying
* {@link Collection} will not update the index and it will get out of sync.
*
*
* If modification of the decorated {@link Collection} is unavoidable, then a
* call to {@link #reindex()} will update the index to the current contents of
* the {@link Collection}.
*
*
* @param the type of object in the index.
* @param the type of object in the collection.
*
* @since 4.0
*/
public class IndexedCollection extends AbstractCollectionDecorator {
// TODO: replace with MultiValuedMap
/** Serialization version */
private static final long serialVersionUID = -5512610452568370038L;
/** The {@link Transformer} for generating index keys. */
private final Transformer keyTransformer;
/** The map of indexes to collected objects. */
private final MultiMap index;
/** The uniqueness constraint for the index. */
private final boolean uniqueIndex;
/**
* Create an {@link IndexedCollection} for a unique index.
*
* If an element is added, which maps to an existing key, an {@link IllegalArgumentException}
* will be thrown.
*
* @param the index object type.
* @param the collection type.
* @param coll the decorated {@link Collection}.
* @param keyTransformer the {@link Transformer} for generating index keys.
* @return the created {@link IndexedCollection}.
*/
public static IndexedCollection uniqueIndexedCollection(final Collection coll,
final Transformer keyTransformer) {
return new IndexedCollection<>(coll, keyTransformer,
MultiValueMap.multiValueMap(new HashMap>()),
true);
}
/**
* Create an {@link IndexedCollection} for a non-unique index.
*
* @param the index object type.
* @param the collection type.
* @param coll the decorated {@link Collection}.
* @param keyTransformer the {@link Transformer} for generating index keys.
* @return the created {@link IndexedCollection}.
*/
public static IndexedCollection nonUniqueIndexedCollection(final Collection coll,
final Transformer keyTransformer) {
return new IndexedCollection<>(coll, keyTransformer,
MultiValueMap.multiValueMap(new HashMap>()),
false);
}
/**
* Create a {@link IndexedCollection}.
*
* @param coll decorated {@link Collection}
* @param keyTransformer {@link Transformer} for generating index keys
* @param map map to use as index
* @param uniqueIndex if the index shall enforce uniqueness of index keys
*/
public IndexedCollection(final Collection coll, final Transformer keyTransformer,
final MultiMap map, final boolean uniqueIndex) {
super(coll);
this.keyTransformer = keyTransformer;
this.index = map;
this.uniqueIndex = uniqueIndex;
reindex();
}
/**
* {@inheritDoc}
*
* @throws IllegalArgumentException if the object maps to an existing key and the index
* enforces a uniqueness constraint
*/
@Override
public boolean add(final C object) {
final boolean added = super.add(object);
if (added) {
addToIndex(object);
}
return added;
}
@Override
public boolean addAll(final Collection coll) {
boolean changed = false;
for (final C c: coll) {
changed |= add(c);
}
return changed;
}
@Override
public void clear() {
super.clear();
index.clear();
}
/**
* {@inheritDoc}
*
* Note: uses the index for fast lookup
*/
@SuppressWarnings("unchecked")
@Override
public boolean contains(final Object object) {
return index.containsKey(keyTransformer.transform((C) object));
}
/**
* {@inheritDoc}
*
* Note: uses the index for fast lookup
*/
@Override
public boolean containsAll(final Collection coll) {
for (final Object o : coll) {
if (!contains(o)) {
return false;
}
}
return true;
}
/**
* Get the element associated with the given key.
*
* In case of a non-unique index, this method will return the first
* value associated with the given key. To retrieve all elements associated
* with a key, use {@link #values(Object)}.
*
* @param key key to look up
* @return element found
* @see #values(Object)
*/
public C get(final K key) {
@SuppressWarnings("unchecked") // index is a MultiMap which returns a Collection
final Collection coll = (Collection) index.get(key);
return coll == null ? null : coll.iterator().next();
}
/**
* Get all elements associated with the given key.
*
* @param key key to look up
* @return a collection of elements found, or null if {@code contains(key) == false}
*/
@SuppressWarnings("unchecked") // index is a MultiMap which returns a Collection
public Collection values(final K key) {
return (Collection) index.get(key);
}
/**
* Clears the index and re-indexes the entire decorated {@link Collection}.
*/
public void reindex() {
index.clear();
for (final C c : decorated()) {
addToIndex(c);
}
}
@SuppressWarnings("unchecked")
@Override
public boolean remove(final Object object) {
final boolean removed = super.remove(object);
if (removed) {
removeFromIndex((C) object);
}
return removed;
}
/**
* @since 4.4
*/
@Override
public boolean removeIf(final Predicate filter) {
if (Objects.isNull(filter)) {
return false;
}
boolean changed = false;
final Iterator it = iterator();
while (it.hasNext()) {
if (filter.test(it.next())) {
it.remove();
changed = true;
}
}
if (changed) {
reindex();
}
return changed;
}
@Override
public boolean removeAll(final Collection coll) {
boolean changed = false;
for (final Object o : coll) {
changed |= remove(o);
}
return changed;
}
@Override
public boolean retainAll(final Collection coll) {
final boolean changed = super.retainAll(coll);
if (changed) {
reindex();
}
return changed;
}
//-----------------------------------------------------------------------
/**
* Provides checking for adding the index.
*
* @param object the object to index
* @throws IllegalArgumentException if the object maps to an existing key and the index
* enforces a uniqueness constraint
*/
private void addToIndex(final C object) {
final K key = keyTransformer.transform(object);
if (uniqueIndex && index.containsKey(key)) {
throw new IllegalArgumentException("Duplicate key in uniquely indexed collection.");
}
index.put(key, object);
}
/**
* Removes an object from the index.
*
* @param object the object to remove
*/
private void removeFromIndex(final C object) {
index.remove(keyTransformer.transform(object));
}
}