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The Apache Commons Collections package contains types that extend and augment the Java Collections Framework.
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/*
* 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.map;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Objects;
import org.apache.commons.collections4.OrderedIterator;
import org.apache.commons.collections4.OrderedMap;
import org.apache.commons.collections4.OrderedMapIterator;
import org.apache.commons.collections4.ResettableIterator;
import org.apache.commons.collections4.iterators.EmptyOrderedIterator;
import org.apache.commons.collections4.iterators.EmptyOrderedMapIterator;
/**
* An abstract implementation of a hash-based map that links entries to create an
* ordered map and which provides numerous points for subclasses to override.
*
* This class implements all the features necessary for a subclass linked
* hash-based map. Key-value entries are stored in instances of the
* {@code LinkEntry} class which can be overridden and replaced.
* The iterators can similarly be replaced, without the need to replace the KeySet,
* EntrySet and Values view classes.
*
*
* Overridable methods are provided to change the default hashing behavior, and
* to change how entries are added to and removed from the map. Hopefully, all you
* need for unusual subclasses is here.
*
*
* This implementation maintains order by original insertion, but subclasses
* may work differently. The {@code OrderedMap} interface is implemented
* to provide access to bidirectional iteration and extra convenience methods.
*
*
* The {@code orderedMapIterator()} method provides direct access to a
* bidirectional iterator. The iterators from the other views can also be cast
* to {@code OrderedIterator} if required.
*
*
* All the available iterators can be reset back to the start by casting to
* {@code ResettableIterator} and calling {@code reset()}.
*
*
* The implementation is also designed to be subclassed, with lots of useful
* methods exposed.
*
*
* @param the type of the keys in this map
* @param the type of the values in this map
* @since 3.0
*/
public abstract class AbstractLinkedMap extends AbstractHashedMap implements OrderedMap {
/**
* EntrySet iterator.
*
* @param the key type.
* @param the value type.
*/
protected static class EntrySetIterator extends LinkIterator implements
OrderedIterator>, ResettableIterator> {
/**
* Constructs a new instance.
*
* @param parent The parent AbstractLinkedMap.
*/
protected EntrySetIterator(final AbstractLinkedMap parent) {
super(parent);
}
@Override
public Map.Entry next() {
return super.nextEntry();
}
@Override
public Map.Entry previous() {
return super.previousEntry();
}
}
/**
* KeySet iterator.
*
* @param the key type.
*/
protected static class KeySetIterator extends LinkIterator implements
OrderedIterator, ResettableIterator {
/**
* Constructs a new instance.
*
* @param parent The parent AbstractLinkedMap.
*/
@SuppressWarnings("unchecked")
protected KeySetIterator(final AbstractLinkedMap parent) {
super((AbstractLinkedMap) parent);
}
@Override
public K next() {
return super.nextEntry().getKey();
}
@Override
public K previous() {
return super.previousEntry().getKey();
}
}
/**
* LinkEntry that stores the data.
*
* If you subclass {@code AbstractLinkedMap} but not {@code LinkEntry}
* then you will not be able to access the protected fields.
* The {@code entryXxx()} methods on {@code AbstractLinkedMap} exist
* to provide the necessary access.
*
*
* @param the key type.
* @param the value type.
*/
protected static class LinkEntry extends HashEntry {
/** The entry before this one in the order */
protected LinkEntry before;
/** The entry after this one in the order */
protected LinkEntry after;
/**
* Constructs a new entry.
*
* @param next the next entry in the hash bucket sequence
* @param hashCode the hash code
* @param key the key
* @param value the value
*/
protected LinkEntry(final HashEntry next, final int hashCode, final Object key, final V value) {
super(next, hashCode, key, value);
}
}
/**
* Base Iterator that iterates in link order.
*
* @param the key type.
* @param the value type.
*/
protected abstract static class LinkIterator {
/** The parent map */
protected final AbstractLinkedMap parent;
/** The current (last returned) entry */
protected LinkEntry last;
/** The next entry */
protected LinkEntry next;
/** The modification count expected */
protected int expectedModCount;
/**
* Constructs a new instance.
*
* @param parent The parent AbstractLinkedMap.
*/
protected LinkIterator(final AbstractLinkedMap parent) {
this.parent = Objects.requireNonNull(parent);
this.next = parent.header.after;
this.expectedModCount = parent.modCount;
}
/**
* Gets the current entry.
*
* @return the current entry.
*/
protected LinkEntry currentEntry() {
return last;
}
/**
* Tests whether there is another entry.
*
* @return whether there is another entry.
*/
public boolean hasNext() {
return next != parent.header;
}
/**
* Tests whether there is a previous entry.
*
* @return whether there is a previous entry.
*/
public boolean hasPrevious() {
return next.before != parent.header;
}
/**
* Gets the next entry.
*
* @return the next entry.
*/
protected LinkEntry nextEntry() {
if (parent.modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
if (next == parent.header) {
throw new NoSuchElementException(NO_NEXT_ENTRY);
}
last = next;
next = next.after;
return last;
}
/**
* Gets the previous entry.
*
* @return the previous entry.
*/
protected LinkEntry previousEntry() {
if (parent.modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
final LinkEntry previous = next.before;
if (previous == parent.header) {
throw new NoSuchElementException(NO_PREVIOUS_ENTRY);
}
next = previous;
last = previous;
return last;
}
/**
* Removes the current entry.
*/
public void remove() {
if (last == null) {
throw new IllegalStateException(REMOVE_INVALID);
}
if (parent.modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
parent.remove(last.getKey());
last = null;
expectedModCount = parent.modCount;
}
/**
* Resets the state to the end.
*/
public void reset() {
last = null;
next = parent.header.after;
}
@Override
public String toString() {
if (last != null) {
return "Iterator[" + last.getKey() + "=" + last.getValue() + "]";
}
return "Iterator[]";
}
}
/**
* MapIterator implementation.
*
* @param the key type.
* @param the value type.
*/
protected static class LinkMapIterator extends LinkIterator implements
OrderedMapIterator, ResettableIterator {
/**
* Constructs a new instance.
*
* @param parent The parent AbstractLinkedMap.
*/
protected LinkMapIterator(final AbstractLinkedMap parent) {
super(parent);
}
@Override
public K getKey() {
final LinkEntry current = currentEntry();
if (current == null) {
throw new IllegalStateException(GETKEY_INVALID);
}
return current.getKey();
}
@Override
public V getValue() {
final LinkEntry current = currentEntry();
if (current == null) {
throw new IllegalStateException(GETVALUE_INVALID);
}
return current.getValue();
}
@Override
public K next() {
return super.nextEntry().getKey();
}
@Override
public K previous() {
return super.previousEntry().getKey();
}
@Override
public V setValue(final V value) {
final LinkEntry current = currentEntry();
if (current == null) {
throw new IllegalStateException(SETVALUE_INVALID);
}
return current.setValue(value);
}
}
/**
* Values iterator.
*
* @param the value type.
*/
protected static class ValuesIterator extends LinkIterator implements
OrderedIterator, ResettableIterator {
/**
* Constructs a new instance.
*
* @param parent The parent AbstractLinkedMap.
*/
@SuppressWarnings("unchecked")
protected ValuesIterator(final AbstractLinkedMap parent) {
super((AbstractLinkedMap) parent);
}
@Override
public V next() {
return super.nextEntry().getValue();
}
@Override
public V previous() {
return super.previousEntry().getValue();
}
}
/** Header in the linked list */
transient LinkEntry header;
/**
* Constructor only used in deserialization, do not use otherwise.
*/
protected AbstractLinkedMap() {
}
/**
* Constructs a new, empty map with the specified initial capacity.
*
* @param initialCapacity the initial capacity
* @throws IllegalArgumentException if the initial capacity is negative
*/
protected AbstractLinkedMap(final int initialCapacity) {
super(initialCapacity);
}
/**
* Constructs a new, empty map with the specified initial capacity and
* load factor.
*
* @param initialCapacity the initial capacity
* @param loadFactor the load factor
* @throws IllegalArgumentException if the initial capacity is negative
* @throws IllegalArgumentException if the load factor is less than zero
*/
protected AbstractLinkedMap(final int initialCapacity, final float loadFactor) {
super(initialCapacity, loadFactor);
}
/**
* Constructor which performs no validation on the passed in parameters.
*
* @param initialCapacity the initial capacity, must be a power of two
* @param loadFactor the load factor, must be > 0.0f and generally < 1.0f
* @param threshold the threshold, must be sensible
*/
protected AbstractLinkedMap(final int initialCapacity, final float loadFactor, final int threshold) {
super(initialCapacity, loadFactor, threshold);
}
/**
* Constructor copying elements from another map.
*
* @param map the map to copy
* @throws NullPointerException if the map is null
*/
protected AbstractLinkedMap(final Map map) {
super(map);
}
/**
* Adds an entry into this map, maintaining insertion order.
*
* This implementation adds the entry to the data storage table and
* to the end of the linked list.
*
*
* @param entry the entry to add
* @param hashIndex the index into the data array to store at
*/
@Override
protected void addEntry(final HashEntry entry, final int hashIndex) {
final LinkEntry link = (LinkEntry) entry;
link.after = header;
link.before = header.before;
header.before.after = link;
header.before = link;
data[hashIndex] = link;
}
/**
* Clears the map, resetting the size to zero and nullifying references
* to avoid garbage collection issues.
*/
@Override
public void clear() {
// override to reset the linked list
super.clear();
header.before = header.after = header;
}
/**
* Checks whether the map contains the specified value.
*
* @param value the value to search for
* @return true if the map contains the value
*/
@Override
public boolean containsValue(final Object value) {
// override uses faster iterator
if (value == null) {
for (LinkEntry entry = header.after; entry != header; entry = entry.after) {
if (entry.getValue() == null) {
return true;
}
}
} else {
for (LinkEntry entry = header.after; entry != header; entry = entry.after) {
if (isEqualValue(value, entry.getValue())) {
return true;
}
}
}
return false;
}
/**
* Creates an entry to store the data.
*
* This implementation creates a new LinkEntry instance.
*
*
* @param next the next entry in sequence
* @param hashCode the hash code to use
* @param key the key to store
* @param value the value to store
* @return the newly created entry
*/
@Override
protected LinkEntry createEntry(final HashEntry next, final int hashCode, final K key, final V value) {
return new LinkEntry<>(next, hashCode, convertKey(key), value);
}
/**
* Creates an entry set iterator.
* Subclasses can override this to return iterators with different properties.
*
* @return the entrySet iterator
*/
@Override
protected Iterator> createEntrySetIterator() {
if (isEmpty()) {
return EmptyOrderedIterator.>emptyOrderedIterator();
}
return new EntrySetIterator<>(this);
}
/**
* Creates a key set iterator.
* Subclasses can override this to return iterators with different properties.
*
* @return the keySet iterator
*/
@Override
protected Iterator createKeySetIterator() {
if (isEmpty()) {
return EmptyOrderedIterator.emptyOrderedIterator();
}
return new KeySetIterator<>(this);
}
/**
* Creates a values iterator.
* Subclasses can override this to return iterators with different properties.
*
* @return the values iterator
*/
@Override
protected Iterator createValuesIterator() {
if (isEmpty()) {
return EmptyOrderedIterator.emptyOrderedIterator();
}
return new ValuesIterator<>(this);
}
/**
* Gets the {@code after} field from a {@code LinkEntry}.
* Used in subclasses that have no visibility of the field.
*
* @param entry the entry to query, must not be null
* @return the {@code after} field of the entry
* @throws NullPointerException if the entry is null
* @since 3.1
*/
protected LinkEntry entryAfter(final LinkEntry entry) {
return entry.after;
}
/**
* Gets the {@code before} field from a {@code LinkEntry}.
* Used in subclasses that have no visibility of the field.
*
* @param entry the entry to query, must not be null
* @return the {@code before} field of the entry
* @throws NullPointerException if the entry is null
* @since 3.1
*/
protected LinkEntry entryBefore(final LinkEntry entry) {
return entry.before;
}
/**
* Gets the first key in the map, which is the first inserted.
*
* @return the eldest key
*/
@Override
public K firstKey() {
if (size == 0) {
throw new NoSuchElementException("Map is empty");
}
return header.after.getKey();
}
/**
* Gets the key at the specified index.
*
* @param index the index to retrieve
* @return the key at the specified index
* @throws IndexOutOfBoundsException if the index is invalid
*/
protected LinkEntry getEntry(final int index) {
if (index < 0) {
throw new IndexOutOfBoundsException("Index " + index + " is less than zero");
}
if (index >= size) {
throw new IndexOutOfBoundsException("Index " + index + " is invalid for size " + size);
}
LinkEntry entry;
if (index < size / 2) {
// Search forwards
entry = header.after;
for (int currentIndex = 0; currentIndex < index; currentIndex++) {
entry = entry.after;
}
} else {
// Search backwards
entry = header;
for (int currentIndex = size; currentIndex > index; currentIndex--) {
entry = entry.before;
}
}
return entry;
}
@Override
protected LinkEntry getEntry(final Object key) {
return (LinkEntry) super.getEntry(key);
}
/**
* Initialize this subclass during construction.
*
* Note: As from v3.2 this method calls
* {@link #createEntry(HashEntry, int, Object, Object)} to create
* the map entry object.
*
*/
@Override
protected void init() {
header = createEntry(null, -1, null, null);
header.before = header.after = header;
}
/**
* Gets the last key in the map, which is the most recently inserted.
*
* @return the most recently inserted key
*/
@Override
public K lastKey() {
if (size == 0) {
throw new NoSuchElementException("Map is empty");
}
return header.before.getKey();
}
/**
* {@inheritDoc}
*/
@Override
public OrderedMapIterator mapIterator() {
if (size == 0) {
return EmptyOrderedMapIterator.emptyOrderedMapIterator();
}
return new LinkMapIterator<>(this);
}
/**
* Gets the next key in sequence.
*
* @param key the key to get after
* @return the next key
*/
@Override
public K nextKey(final Object key) {
final LinkEntry entry = getEntry(key);
return entry == null || entry.after == header ? null : entry.after.getKey();
}
/**
* Gets the previous key in sequence.
*
* @param key the key to get before
* @return the previous key
*/
@Override
public K previousKey(final Object key) {
final LinkEntry entry = getEntry(key);
return entry == null || entry.before == header ? null : entry.before.getKey();
}
/**
* Removes an entry from the map and the linked list.
*
* This implementation removes the entry from the linked list chain, then
* calls the superclass implementation.
*
*
* @param entry the entry to remove
* @param hashIndex the index into the data structure
* @param previous the previous entry in the chain
*/
@Override
protected void removeEntry(final HashEntry entry, final int hashIndex, final HashEntry previous) {
final LinkEntry link = (LinkEntry) entry;
link.before.after = link.after;
link.after.before = link.before;
link.after = null;
link.before = null;
super.removeEntry(entry, hashIndex, previous);
}
}
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