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The Commons Collections AbstractLinkedMap.java source code
/*
* 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.collections.map;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import org.apache.commons.collections.MapIterator;
import org.apache.commons.collections.OrderedIterator;
import org.apache.commons.collections.OrderedMap;
import org.apache.commons.collections.OrderedMapIterator;
import org.apache.commons.collections.ResettableIterator;
import org.apache.commons.collections.iterators.EmptyOrderedIterator;
import org.apache.commons.collections.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.
* <p>
* 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.
* <p>
* Overridable methods are provided to change the default hashing behaviour, and
* to change how entries are added to and removed from the map. Hopefully, all you
* need for unusual subclasses is here.
* <p>
* 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.
* <p>
* 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.
* <p>
* All the available iterators can be reset back to the start by casting to
* <code>ResettableIterator and calling reset().
* <p>
* The implementation is also designed to be subclassed, with lots of useful
* methods exposed.
*
* @since Commons Collections 3.0
* @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
*
* @author java util LinkedHashMap
* @author Stephen Colebourne
*/
public class AbstractLinkedMap extends AbstractHashedMap implements OrderedMap {
/** Header in the linked list */
protected transient LinkEntry header;
/**
* Constructor only used in deserialization, do not use otherwise.
*/
protected AbstractLinkedMap() {
super();
}
/**
* 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(int initialCapacity, float loadFactor, int threshold) {
super(initialCapacity, loadFactor, threshold);
}
/**
* Constructs a new, empty map with the specified initial capacity.
*
* @param initialCapacity the initial capacity
* @throws IllegalArgumentException if the initial capacity is less than one
*/
protected AbstractLinkedMap(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 less than one
* @throws IllegalArgumentException if the load factor is less than zero
*/
protected AbstractLinkedMap(int initialCapacity, float loadFactor) {
super(initialCapacity, loadFactor);
}
/**
* Constructor copying elements from another map.
*
* @param map the map to copy
* @throws NullPointerException if the map is null
*/
protected AbstractLinkedMap(Map map) {
super(map);
}
/**
* Initialise this subclass during construction.
* <p>
* NOTE: As from v3.2 this method calls
* {@link #createEntry(HashEntry, int, Object, Object)} to create
* the map entry object.
*/
protected void init() {
header = (LinkEntry) createEntry(null, -1, null, null);
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
*/
public boolean containsValue(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;
}
/**
* Clears the map, resetting the size to zero and nullifying references
* to avoid garbage collection issues.
*/
public void clear() {
// override to reset the linked list
super.clear();
header.before = header.after = header;
}
//-----------------------------------------------------------------------
/**
* Gets the first key in the map, which is the most recently inserted.
*
* @return the most recently inserted key
*/
public Object firstKey() {
if (size == 0) {
throw new NoSuchElementException("Map is empty");
}
return header.after.getKey();
}
/**
* Gets the last key in the map, which is the first inserted.
*
* @return the eldest key
*/
public Object lastKey() {
if (size == 0) {
throw new NoSuchElementException("Map is empty");
}
return header.before.getKey();
}
/**
* Gets the next key in sequence.
*
* @param key the key to get after
* @return the next key
*/
public Object nextKey(Object key) {
LinkEntry entry = (LinkEntry) 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
*/
public Object previousKey(Object key) {
LinkEntry entry = (LinkEntry) getEntry(key);
return (entry == null || entry.before == header ? null : entry.before.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(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;
}
/**
* Adds an entry into this map, maintaining insertion order.
* <p>
* 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
*/
protected void addEntry(HashEntry entry, int hashIndex) {
LinkEntry link = (LinkEntry) entry;
link.after = header;
link.before = header.before;
header.before.after = link;
header.before = link;
data[hashIndex] = entry;
}
/**
* Creates an entry to store the data.
* <p>
* 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
*/
protected HashEntry createEntry(HashEntry next, int hashCode, Object key, Object value) {
return new LinkEntry(next, hashCode, key, value);
}
/**
* Removes an entry from the map and the linked list.
* <p>
* 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
*/
protected void removeEntry(HashEntry entry, int hashIndex, HashEntry previous) {
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);
}
//-----------------------------------------------------------------------
/**
* Gets the <code>before field from a 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 Commons Collections 3.1
*/
protected LinkEntry entryBefore(LinkEntry entry) {
return entry.before;
}
/**
* Gets the <code>after field from a 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 Commons Collections 3.1
*/
protected LinkEntry entryAfter(LinkEntry entry) {
return entry.after;
}
//-----------------------------------------------------------------------
/**
* Gets an iterator over the map.
* Changes made to the iterator affect this map.
* <p>
* A MapIterator returns the keys in the map. It also provides convenient
* methods to get the key and value, and set the value.
* It avoids the need to create an entrySet/keySet/values object.
*
* @return the map iterator
*/
public MapIterator mapIterator() {
if (size == 0) {
return EmptyOrderedMapIterator.INSTANCE;
}
return new LinkMapIterator(this);
}
/**
* Gets a bidirectional iterator over the map.
* Changes made to the iterator affect this map.
* <p>
* A MapIterator returns the keys in the map. It also provides convenient
* methods to get the key and value, and set the value.
* It avoids the need to create an entrySet/keySet/values object.
*
* @return the map iterator
*/
public OrderedMapIterator orderedMapIterator() {
if (size == 0) {
return EmptyOrderedMapIterator.INSTANCE;
}
return new LinkMapIterator(this);
}
/**
* MapIterator implementation.
*/
protected static class LinkMapIterator extends LinkIterator implements OrderedMapIterator {
protected LinkMapIterator(AbstractLinkedMap parent) {
super(parent);
}
public Object next() {
return super.nextEntry().getKey();
}
public Object previous() {
return super.previousEntry().getKey();
}
public Object getKey() {
HashEntry current = currentEntry();
if (current == null) {
throw new IllegalStateException(AbstractHashedMap.GETKEY_INVALID);
}
return current.getKey();
}
public Object getValue() {
HashEntry current = currentEntry();
if (current == null) {
throw new IllegalStateException(AbstractHashedMap.GETVALUE_INVALID);
}
return current.getValue();
}
public Object setValue(Object value) {
HashEntry current = currentEntry();
if (current == null) {
throw new IllegalStateException(AbstractHashedMap.SETVALUE_INVALID);
}
return current.setValue(value);
}
}
//-----------------------------------------------------------------------
/**
* Creates an entry set iterator.
* Subclasses can override this to return iterators with different properties.
*
* @return the entrySet iterator
*/
protected Iterator createEntrySetIterator() {
if (size() == 0) {
return EmptyOrderedIterator.INSTANCE;
}
return new EntrySetIterator(this);
}
/**
* EntrySet iterator.
*/
protected static class EntrySetIterator extends LinkIterator {
protected EntrySetIterator(AbstractLinkedMap parent) {
super(parent);
}
public Object next() {
return super.nextEntry();
}
public Object previous() {
return super.previousEntry();
}
}
//-----------------------------------------------------------------------
/**
* Creates a key set iterator.
* Subclasses can override this to return iterators with different properties.
*
* @return the keySet iterator
*/
protected Iterator createKeySetIterator() {
if (size() == 0) {
return EmptyOrderedIterator.INSTANCE;
}
return new KeySetIterator(this);
}
/**
* KeySet iterator.
*/
protected static class KeySetIterator extends EntrySetIterator {
protected KeySetIterator(AbstractLinkedMap parent) {
super(parent);
}
public Object next() {
return super.nextEntry().getKey();
}
public Object previous() {
return super.previousEntry().getKey();
}
}
//-----------------------------------------------------------------------
/**
* Creates a values iterator.
* Subclasses can override this to return iterators with different properties.
*
* @return the values iterator
*/
protected Iterator createValuesIterator() {
if (size() == 0) {
return EmptyOrderedIterator.INSTANCE;
}
return new ValuesIterator(this);
}
/**
* Values iterator.
*/
protected static class ValuesIterator extends LinkIterator {
protected ValuesIterator(AbstractLinkedMap parent) {
super(parent);
}
public Object next() {
return super.nextEntry().getValue();
}
public Object previous() {
return super.previousEntry().getValue();
}
}
//-----------------------------------------------------------------------
/**
* LinkEntry that stores the data.
* <p>
* If you subclass <code>AbstractLinkedMap but not LinkEntry
* then you will not be able to access the protected fields.
* The <code>entryXxx() methods on AbstractLinkedMap exist
* to provide the necessary access.
*/
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(HashEntry next, int hashCode, Object key, Object value) {
super(next, hashCode, key, value);
}
}
/**
* Base Iterator that iterates in link order.
*/
protected static abstract class LinkIterator
implements OrderedIterator, ResettableIterator {
/** 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;
protected LinkIterator(AbstractLinkedMap parent) {
super();
this.parent = parent;
this.next = parent.header.after;
this.expectedModCount = parent.modCount;
}
public boolean hasNext() {
return (next != parent.header);
}
public boolean hasPrevious() {
return (next.before != parent.header);
}
protected LinkEntry nextEntry() {
if (parent.modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
if (next == parent.header) {
throw new NoSuchElementException(AbstractHashedMap.NO_NEXT_ENTRY);
}
last = next;
next = next.after;
return last;
}
protected LinkEntry previousEntry() {
if (parent.modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
LinkEntry previous = next.before;
if (previous == parent.header) {
throw new NoSuchElementException(AbstractHashedMap.NO_PREVIOUS_ENTRY);
}
next = previous;
last = previous;
return last;
}
protected LinkEntry currentEntry() {
return last;
}
public void remove() {
if (last == null) {
throw new IllegalStateException(AbstractHashedMap.REMOVE_INVALID);
}
if (parent.modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
parent.remove(last.getKey());
last = null;
expectedModCount = parent.modCount;
}
public void reset() {
last = null;
next = parent.header.after;
}
public String toString() {
if (last != null) {
return "Iterator[" + last.getKey() + "=" + last.getValue() + "]";
} else {
return "Iterator[]";
}
}
}
}
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