MapWithOrdinalImpl.java
/*
* 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.arrow.vector.util;
import java.util.AbstractMap;
import java.util.ArrayList;
import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.stream.Collectors;
/**
* An implementation of map that supports constant time look-up by a generic key or an ordinal.
*
* <p>This class extends the functionality a regular {@link Map} with ordinal lookup support. Upon
* insertion an unused ordinal is assigned to the inserted (key, value) tuple. Upon update the same
* ordinal id is re-used while value is replaced. Upon deletion of an existing item, its
* corresponding ordinal is recycled and could be used by another item.
*
* <p>For any instance with N items, this implementation guarantees that ordinals are in the range
* of [0, N). However, the ordinal assignment is dynamic and may change after an insertion or
* deletion. Consumers of this class are responsible for explicitly checking the ordinal
* corresponding to a key via {@link MapWithOrdinalImpl#getOrdinal(Object)} before attempting to
* execute a lookup with an ordinal.
*
* @param <K> key type
* @param <V> value type
*/
public class MapWithOrdinalImpl<K, V> implements MapWithOrdinal<K, V> {
private final Map<K, Map.Entry<Integer, V>> primary = new LinkedHashMap<>();
private final IntObjectHashMap<V> secondary = new IntObjectHashMap<>();
private final Map<K, V> delegate =
new Map<K, V>() {
@Override
public boolean isEmpty() {
return size() == 0;
}
@Override
public int size() {
return primary.size();
}
@Override
public boolean containsKey(Object key) {
return primary.containsKey(key);
}
@Override
public boolean containsValue(Object value) {
return primary.containsValue(value);
}
@Override
public V get(Object key) {
Entry<Integer, V> pair = primary.get(key);
if (pair != null) {
return pair.getValue();
}
return null;
}
@Override
public V put(K key, V value) {
final Entry<Integer, V> oldPair = primary.get(key);
// if key exists try replacing otherwise, assign a new ordinal identifier
final int ordinal = oldPair == null ? primary.size() : oldPair.getKey();
primary.put(key, new AbstractMap.SimpleImmutableEntry<>(ordinal, value));
secondary.put(ordinal, value);
return oldPair == null ? null : oldPair.getValue();
}
@Override
public V remove(Object key) {
final Entry<Integer, V> oldPair = primary.remove(key);
if (oldPair != null) {
final int lastOrdinal = secondary.size();
final V last = secondary.get(lastOrdinal);
// normalize mappings so that all numbers until primary.size() is assigned
// swap the last element with the deleted one
secondary.put(oldPair.getKey(), last);
primary.put((K) key, new AbstractMap.SimpleImmutableEntry<>(oldPair.getKey(), last));
}
return oldPair == null ? null : oldPair.getValue();
}
@Override
public void putAll(Map<? extends K, ? extends V> m) {
throw new UnsupportedOperationException();
}
@Override
public void clear() {
primary.clear();
secondary.clear();
}
@Override
public Set<K> keySet() {
return primary.keySet();
}
@Override
public Collection<V> values() {
return secondary.values();
}
@Override
public Set<Entry<K, V>> entrySet() {
return primary.entrySet().stream()
.map(
entry ->
new AbstractMap.SimpleImmutableEntry<>(
entry.getKey(), entry.getValue().getValue()))
.collect(Collectors.toSet());
}
};
/**
* Returns the value corresponding to the given ordinal.
*
* @param id ordinal value for lookup
* @return an instance of V
*/
@Override
public V getByOrdinal(int id) {
return secondary.get(id);
}
/**
* Returns the ordinal corresponding to the given key.
*
* @param key key for ordinal lookup
* @return ordinal value corresponding to key if it exists or -1
*/
@Override
public int getOrdinal(K key) {
Map.Entry<Integer, V> pair = primary.get(key);
if (pair != null) {
return pair.getKey();
}
return -1;
}
@Override
public int size() {
return delegate.size();
}
@Override
public boolean isEmpty() {
return delegate.isEmpty();
}
@Override
public Collection<V> getAll(K key) {
if (delegate.containsKey(key)) {
List<V> list = new ArrayList<>(1);
list.add(get(key));
return list;
}
return null;
}
@Override
public V get(K key) {
return delegate.get(key);
}
/**
* Inserts the tuple (key, value) into the map extending the semantics of {@link Map#put} with
* automatic ordinal assignment. A new ordinal is assigned if key does not exists. Otherwise the
* same ordinal is re-used but the value is replaced.
*
* @see java.util.Map#put
*/
@Override
public boolean put(K key, V value, boolean overwrite) {
return delegate.put(key, value) != null;
}
@Override
public Collection<V> values() {
return delegate.values();
}
@Override
public boolean remove(K key, V value) {
return false;
}
@Override
public boolean containsKey(Object key) {
return delegate.containsKey(key);
}
/**
* Removes the element corresponding to the key if exists extending the semantics of {@link
* java.util.Map#remove} with ordinal re-cycling. The ordinal corresponding to the given key may
* be re-assigned to another tuple. It is important that consumer checks the ordinal value via
* {@link MapWithOrdinalImpl#getOrdinal(Object)} before attempting to look-up by ordinal.
*
* @see java.util.Map#remove
*/
@Override
public boolean removeAll(K key) {
return delegate.remove(key) != null;
}
@Override
public void clear() {
delegate.clear();
}
@Override
public Set<K> keys() {
return delegate.keySet();
}
}