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 * 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
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 *      http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.commons.collections4.map;

import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;

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 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 behaviour, 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 OrderedMap interface is implemented to provide access to bidirectional iteration and extra convenience methods.

The orderedMapIterator() method provides direct access to a bidirectional iterator. The iterators from the other views can also be cast to OrderedIterator if required.

All the available iterators can be reset back to the start by casting to ResettableIterator and calling reset().

The implementation is also designed to be subclassed, with lots of useful methods exposed.

Type parameters:
  • <K> – the type of the keys in this map
  • <V> – the type of the values in this map
Since:3.0
/** * 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</code> 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</code> interface is implemented * to provide access to bidirectional iteration and extra convenience methods. * <p> * The <code>orderedMapIterator()</code> method provides direct access to a * bidirectional iterator. The iterators from the other views can also be cast * to <code>OrderedIterator</code> if required. * <p> * All the available iterators can be reset back to the start by casting to * <code>ResettableIterator</code> and calling <code>reset()</code>. * <p> * The implementation is also designed to be subclassed, with lots of useful * methods exposed. * * @param <K> the type of the keys in this map * @param <V> the type of the values in this map * @since 3.0 */
public abstract class AbstractLinkedMap<K, V> extends AbstractHashedMap<K, V> implements OrderedMap<K, V> {
Header in the linked list
/** Header in the linked list */
transient LinkEntry<K, V> header;
Constructor only used in deserialization, do not use otherwise.
/** * Constructor only used in deserialization, do not use otherwise. */
protected AbstractLinkedMap() { super(); }
Constructor which performs no validation on the passed in parameters.
Params:
  • initialCapacity – the initial capacity, must be a power of two
  • loadFactor – the load factor, must be > 0.0f and generally < 1.0f
  • threshold – the threshold, must be sensible
/** * 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 &gt; 0.0f and generally &lt; 1.0f * @param threshold the threshold, must be sensible */
protected AbstractLinkedMap(final int initialCapacity, final float loadFactor, final int threshold) { super(initialCapacity, loadFactor, threshold); }
Constructs a new, empty map with the specified initial capacity.
Params:
  • initialCapacity – the initial capacity
Throws:
/** * 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.
Params:
  • initialCapacity – the initial capacity
  • loadFactor – the load factor
Throws:
/** * 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 copying elements from another map.
Params:
  • map – the map to copy
Throws:
/** * Constructor copying elements from another map. * * @param map the map to copy * @throws NullPointerException if the map is null */
protected AbstractLinkedMap(final Map<? extends K, ? extends V> map) { super(map); }
Initialise this subclass during construction.

NOTE: As from v3.2 this method calls createEntry(HashEntry, int, Object, Object) to create the map entry object.

/** * 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. */
@Override protected void init() { header = createEntry(null, -1, null, null); header.before = header.after = header; } //-----------------------------------------------------------------------
Checks whether the map contains the specified value.
Params:
  • value – the value to search for
Returns:true if the map contains the value
/** * 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<K, V> entry = header.after; entry != header; entry = entry.after) { if (entry.getValue() == null) { return true; } } } else { for (LinkEntry<K, V> 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.
/** * 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; } //-----------------------------------------------------------------------
Gets the first key in the map, which is the first inserted.
Returns:the eldest key
/** * 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 last key in the map, which is the most recently inserted.
Returns:the most recently inserted key
/** * 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(); }
Gets the next key in sequence.
Params:
  • key – the key to get after
Returns:the next key
/** * 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<K, V> entry = getEntry(key); return entry == null || entry.after == header ? null : entry.after.getKey(); } @Override protected LinkEntry<K, V> getEntry(final Object key) { return (LinkEntry<K, V>) super.getEntry(key); }
Gets the previous key in sequence.
Params:
  • key – the key to get before
Returns:the previous key
/** * 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<K, V> entry = getEntry(key); return entry == null || entry.before == header ? null : entry.before.getKey(); } //-----------------------------------------------------------------------
Gets the key at the specified index.
Params:
  • index – the index to retrieve
Throws:
Returns:the key at the specified index
/** * 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<K, V> 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<K, V> 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.

This implementation adds the entry to the data storage table and to the end of the linked list.

Params:
  • entry – the entry to add
  • hashIndex – the index into the data array to store at
/** * 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 */
@Override protected void addEntry(final HashEntry<K, V> entry, final int hashIndex) { final LinkEntry<K, V> link = (LinkEntry<K, V>) entry; link.after = header; link.before = header.before; header.before.after = link; header.before = link; data[hashIndex] = link; }
Creates an entry to store the data.

This implementation creates a new LinkEntry instance.

Params:
  • next – the next entry in sequence
  • hashCode – the hash code to use
  • key – the key to store
  • value – the value to store
Returns:the newly created 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 */
@Override protected LinkEntry<K, V> createEntry(final HashEntry<K, V> next, final int hashCode, final K key, final V value) { return new LinkEntry<>(next, hashCode, convertKey(key), value); }
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.

Params:
  • entry – the entry to remove
  • hashIndex – the index into the data structure
  • previous – the previous entry in the chain
/** * 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 */
@Override protected void removeEntry(final HashEntry<K, V> entry, final int hashIndex, final HashEntry<K, V> previous) { final LinkEntry<K, V> link = (LinkEntry<K, V>) entry; link.before.after = link.after; link.after.before = link.before; link.after = null; link.before = null; super.removeEntry(entry, hashIndex, previous); } //-----------------------------------------------------------------------
Gets the before field from a LinkEntry. Used in subclasses that have no visibility of the field.
Params:
  • entry – the entry to query, must not be null
Throws:
Returns:the before field of the entry
Since:3.1
/** * Gets the <code>before</code> field from a <code>LinkEntry</code>. * Used in subclasses that have no visibility of the field. * * @param entry the entry to query, must not be null * @return the <code>before</code> field of the entry * @throws NullPointerException if the entry is null * @since 3.1 */
protected LinkEntry<K, V> entryBefore(final LinkEntry<K, V> entry) { return entry.before; }
Gets the after field from a LinkEntry. Used in subclasses that have no visibility of the field.
Params:
  • entry – the entry to query, must not be null
Throws:
Returns:the after field of the entry
Since:3.1
/** * Gets the <code>after</code> field from a <code>LinkEntry</code>. * Used in subclasses that have no visibility of the field. * * @param entry the entry to query, must not be null * @return the <code>after</code> field of the entry * @throws NullPointerException if the entry is null * @since 3.1 */
protected LinkEntry<K, V> entryAfter(final LinkEntry<K, V> entry) { return entry.after; } //-----------------------------------------------------------------------
{@inheritDoc}
/** * {@inheritDoc} */
@Override public OrderedMapIterator<K, V> mapIterator() { if (size == 0) { return EmptyOrderedMapIterator.<K, V>emptyOrderedMapIterator(); } return new LinkMapIterator<>(this); }
MapIterator implementation.
/** * MapIterator implementation. */
protected static class LinkMapIterator<K, V> extends LinkIterator<K, V> implements OrderedMapIterator<K, V>, ResettableIterator<K> { protected LinkMapIterator(final AbstractLinkedMap<K, V> parent) { super(parent); } @Override public K next() { return super.nextEntry().getKey(); } @Override public K previous() { return super.previousEntry().getKey(); } @Override public K getKey() { final LinkEntry<K, V> current = currentEntry(); if (current == null) { throw new IllegalStateException(AbstractHashedMap.GETKEY_INVALID); } return current.getKey(); } @Override public V getValue() { final LinkEntry<K, V> current = currentEntry(); if (current == null) { throw new IllegalStateException(AbstractHashedMap.GETVALUE_INVALID); } return current.getValue(); } @Override public V setValue(final V value) { final LinkEntry<K, V> 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.
Returns:the entrySet iterator
/** * Creates an entry set iterator. * Subclasses can override this to return iterators with different properties. * * @return the entrySet iterator */
@Override protected Iterator<Map.Entry<K, V>> createEntrySetIterator() { if (size() == 0) { return EmptyOrderedIterator.<Map.Entry<K, V>>emptyOrderedIterator(); } return new EntrySetIterator<>(this); }
EntrySet iterator.
/** * EntrySet iterator. */
protected static class EntrySetIterator<K, V> extends LinkIterator<K, V> implements OrderedIterator<Map.Entry<K, V>>, ResettableIterator<Map.Entry<K, V>> { protected EntrySetIterator(final AbstractLinkedMap<K, V> parent) { super(parent); } @Override public Map.Entry<K, V> next() { return super.nextEntry(); } @Override public Map.Entry<K, V> previous() { return super.previousEntry(); } } //-----------------------------------------------------------------------
Creates a key set iterator. Subclasses can override this to return iterators with different properties.
Returns:the keySet iterator
/** * Creates a key set iterator. * Subclasses can override this to return iterators with different properties. * * @return the keySet iterator */
@Override protected Iterator<K> createKeySetIterator() { if (size() == 0) { return EmptyOrderedIterator.<K>emptyOrderedIterator(); } return new KeySetIterator<>(this); }
KeySet iterator.
/** * KeySet iterator. */
protected static class KeySetIterator<K> extends LinkIterator<K, Object> implements OrderedIterator<K>, ResettableIterator<K> { @SuppressWarnings("unchecked") protected KeySetIterator(final AbstractLinkedMap<K, ?> parent) { super((AbstractLinkedMap<K, Object>) parent); } @Override public K next() { return super.nextEntry().getKey(); } @Override public K previous() { return super.previousEntry().getKey(); } } //-----------------------------------------------------------------------
Creates a values iterator. Subclasses can override this to return iterators with different properties.
Returns:the values iterator
/** * Creates a values iterator. * Subclasses can override this to return iterators with different properties. * * @return the values iterator */
@Override protected Iterator<V> createValuesIterator() { if (size() == 0) { return EmptyOrderedIterator.<V>emptyOrderedIterator(); } return new ValuesIterator<>(this); }
Values iterator.
/** * Values iterator. */
protected static class ValuesIterator<V> extends LinkIterator<Object, V> implements OrderedIterator<V>, ResettableIterator<V> { @SuppressWarnings("unchecked") protected ValuesIterator(final AbstractLinkedMap<?, V> parent) { super((AbstractLinkedMap<Object, V>) parent); } @Override public V next() { return super.nextEntry().getValue(); } @Override public V previous() { return super.previousEntry().getValue(); } } //-----------------------------------------------------------------------
LinkEntry that stores the data.

If you subclass AbstractLinkedMap but not LinkEntry then you will not be able to access the protected fields. The entryXxx() methods on AbstractLinkedMap exist to provide the necessary access.

/** * LinkEntry that stores the data. * <p> * If you subclass <code>AbstractLinkedMap</code> but not <code>LinkEntry</code> * then you will not be able to access the protected fields. * The <code>entryXxx()</code> methods on <code>AbstractLinkedMap</code> exist * to provide the necessary access. */
protected static class LinkEntry<K, V> extends HashEntry<K, V> {
The entry before this one in the order
/** The entry before this one in the order */
protected LinkEntry<K, V> before;
The entry after this one in the order
/** The entry after this one in the order */
protected LinkEntry<K, V> after;
Constructs a new entry.
Params:
  • next – the next entry in the hash bucket sequence
  • hashCode – the hash code
  • key – the key
  • value – the value
/** * 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<K, V> next, final int hashCode, final Object key, final V value) { super(next, hashCode, key, value); } }
Base Iterator that iterates in link order.
/** * Base Iterator that iterates in link order. */
protected static abstract class LinkIterator<K, V> {
The parent map
/** The parent map */
protected final AbstractLinkedMap<K, V> parent;
The current (last returned) entry
/** The current (last returned) entry */
protected LinkEntry<K, V> last;
The next entry
/** The next entry */
protected LinkEntry<K, V> next;
The modification count expected
/** The modification count expected */
protected int expectedModCount; protected LinkIterator(final AbstractLinkedMap<K, V> 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<K, V> 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<K, V> previousEntry() { if (parent.modCount != expectedModCount) { throw new ConcurrentModificationException(); } final LinkEntry<K, V> previous = next.before; if (previous == parent.header) { throw new NoSuchElementException(AbstractHashedMap.NO_PREVIOUS_ENTRY); } next = previous; last = previous; return last; } protected LinkEntry<K, V> 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; } @Override public String toString() { if (last != null) { return "Iterator[" + last.getKey() + "=" + last.getValue() + "]"; } return "Iterator[]"; } } }