abstractlinkedmap.java

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/*
 *  Copyright 2003-2004 The Apache Software Foundation
 *
 *  Licensed 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</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.
 * 
 * @since Commons Collections 3.0
 * @version $Revision: 158688 $ $Date: 2005-03-22 22:14:15 +0000 (Tue, 22 Mar 2005) $
 *
 * @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</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 Commons Collections 3.1