/*
 *  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.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.AbstractCollection;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;

import org.apache.commons.collections.IterableMap;
import org.apache.commons.collections.IteratorUtils;
import org.apache.commons.collections.KeyValue;
import org.apache.commons.collections.MapIterator;

/**
 * An abstract implementation of a hash-based map which provides numerous points for
 * subclasses to override.
 * <p>
 * This class implements all the features necessary for a subclass hash-based map.
 * Key-value entries are stored in instances of the <code>HashEntry</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.
 * 
 * @since Commons Collections 3.0
 * @version $Revision: 1.1 $ $Date: 2004/03/27 00:07:13 $
 *
 * @author java util HashMap
 * @author Stephen Colebourne
 */
public class AbstractHashedMap implements IterableMap {
    
    protected static final String NO_NEXT_ENTRY = "No next() entry in the iteration";
    protected static final String NO_PREVIOUS_ENTRY = "No previous() entry in the iteration";
    protected static final String REMOVE_INVALID = "remove() can only be called once after next()";
    protected static final String GETKEY_INVALID = "getKey() can only be called after next() and before remove()";
    protected static final String GETVALUE_INVALID = "getValue() can only be called after next() and before remove()";
    protected static final String SETVALUE_INVALID = "setValue() can only be called after next() and before remove()";
    
    /** The default capacity to use */
    protected static final int DEFAULT_CAPACITY = 16;
    /** The default threshold to use */
    protected static final int DEFAULT_THRESHOLD = 12;
    /** The default load factor to use */
    protected static final float DEFAULT_LOAD_FACTOR = 0.75f;
    /** The maximum capacity allowed */
    protected static final int MAXIMUM_CAPACITY = 1 << 30;
    /** An object for masking null */
    protected static final Object NULL = new Object();
    
    /** Load factor, normally 0.75 */
    protected transient float loadFactor;
    /** The size of the map */
    protected transient int size;
    /** Map entries */
    protected transient HashEntry[] data;
    /** Size at which to rehash */
    protected transient int threshold;
    /** Modification count for iterators */
    protected transient int modCount;
    /** Entry set */
    protected transient EntrySet entrySet;
    /** Key set */
    protected transient KeySet keySet;
    /** Values */
    protected transient Values values;

    /**
     * Constructor only used in deserialization, do not use otherwise.
     */
    protected AbstractHashedMap() {
        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 &gt; 0.0f and generally &lt; 1.0f
     * @param threshold  the threshold, must be sensible
     */
    protected AbstractHashedMap(int initialCapacity, float loadFactor, int threshold) {
        super();
        this.loadFactor = loadFactor;
        this.data = new HashEntry[initialCapacity];
        this.threshold = threshold;
        init();
    }

    /**
     * Constructs a new, empty map with the specified initial capacity and
     * default load factor. 
     *
     * @param initialCapacity  the initial capacity
     * @throws IllegalArgumentException if the initial capacity is less than one
     */
    protected AbstractHashedMap(int initialCapacity) {
        this(initialCapacity, DEFAULT_LOAD_FACTOR);
    }

    /**
     * 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 or equal to zero
     */
    protected AbstractHashedMap(int initialCapacity, float loadFactor) {
        super();
        if (initialCapacity < 1) {
            throw new IllegalArgumentException("Initial capacity must be greater than 0");
        }
        if (loadFactor <= 0.0f || Float.isNaN(loadFactor)) {
            throw new IllegalArgumentException("Load factor must be greater than 0");
        }
        this.loadFactor = loadFactor;
        this.threshold = calculateThreshold(initialCapacity, loadFactor);
        initialCapacity = calculateNewCapacity(initialCapacity);
        this.data = new HashEntry[initialCapacity];
        init();
    }

    /**
     * Constructor copying elements from another map.
     *
     * @param map  the map to copy
     * @throws NullPointerException if the map is null
     */
    protected AbstractHashedMap(Map map) {
        this(Math.max(2 * map.size(), DEFAULT_CAPACITY), DEFAULT_LOAD_FACTOR);
        putAll(map);
    }

    /**
     * Initialise subclasses during construction, cloning or deserialization.
     */
    protected void init() {
    }

    //-----------------------------------------------------------------------
    /**
     * Gets the value mapped to the key specified.
     * 
     * @param key  the key
     * @return the mapped value, null if no match
     */
    public Object get(Object key) {
        key = convertKey(key);
        int hashCode = hash(key);
        HashEntry entry = data[hashIndex(hashCode, data.length)]; // no local for hash index
        while (entry != null) {
            if (entry.hashCode == hashCode && isEqualKey(key, entry.key)) {
                return entry.getValue();
            }
            entry = entry.next;
        }
        return null;
    }

    /**
     * Gets the size of the map.
     * 
     * @return the size
     */
    public int size() {
        return size;
    }

    /**
     * Checks whether the map is currently empty.
     * 
     * @return true if the map is currently size zero
     */
    public boolean isEmpty() {
        return (size == 0);
    }

    //-----------------------------------------------------------------------
    /**
     * Checks whether the map contains the specified key.
     * 
     * @param key  the key to search for
     * @return true if the map contains the key
     */
    public boolean containsKey(Object key) {
        key = convertKey(key);
        int hashCode = hash(key);
        HashEntry entry = data[hashIndex(hashCode, data.length)]; // no local for hash index
        while (entry != null) {
            if (entry.hashCode == hashCode && isEqualKey(key, entry.key)) {
                return true;
            }
            entry = entry.next;
        }
        return false;
    }

    /**
     * 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) {
        if (value == null) {
            for (int i = 0, isize = data.length; i < isize; i++) {
                HashEntry entry = data[i];
                while (entry != null) {
                    if (entry.getValue() == null) {
                        return true;
                    }
                    entry = entry.next;
                }
            }
        } else {
            for (int i = 0, isize = data.length; i < isize; i++) {
                HashEntry entry = data[i];
                while (entry != null) {
                    if (isEqualValue(value, entry.getValue())) {
                        return true;
                    }
                    entry = entry.next;
                }
            }
        }
        return false;
    }

    //-----------------------------------------------------------------------
    /**
     * Puts a key-value mapping into this map.
     * 
     * @param key  the key to add
     * @param value  the value to add
     * @return the value previously mapped to this key, null if none
     */
    public Object put(Object key, Object value) {
        key = convertKey(key);
        int hashCode = hash(key);
        int index = hashIndex(hashCode, data.length);
        HashEntry entry = data[index];
        while (entry != null) {
            if (entry.hashCode == hashCode && isEqualKey(key, entry.key)) {
                Object oldValue = entry.getValue();
                updateEntry(entry, value);
                return oldValue;
            }
            entry = entry.next;
        }
        
        addMapping(index, hashCode, key, value);
        return null;
    }

    /**
     * Puts all the values from the specified map into this map.
     * 
     * @param map  the map to add
     * @throws NullPointerException if the map is null
     */
    public void putAll(Map map) {
        int mapSize = map.size();
        if (mapSize == 0) {
            return;
        }
        ensureCapacity(calculateNewCapacity(size + mapSize));
        for (Iterator it = map.entrySet().iterator(); it.hasNext();) {
            Map.Entry entry = (Map.Entry) it.next();
            put(entry.getKey(), entry.getValue());
        }
    }

    /**
     * Removes the specified mapping from this map.
     * 
     * @param key  the mapping to remove
     * @return the value mapped to the removed key, null if key not in map
     */
    public Object remove(Object key) {
        key = convertKey(key);
        int hashCode = hash(key);
        int index = hashIndex(hashCode, data.length);
        HashEntry entry = data[index];
        HashEntry previous = null;
        while (entry != null) {
            if (entry.hashCode == hashCode && isEqualKey(key, entry.key)) {
                Object oldValue = entry.getValue();
                removeMapping(entry, index, previous);
                return oldValue;
            }
            previous = entry;
            entry = entry.next;
        }
        return null;
    }

    /**
     * Clears the map, resetting the size to zero and nullifying references
     * to avoid garbage collection issues.
     */
    public void clear() {
        modCount++;
        HashEntry[] data = this.data;
        for (int i = data.length - 1; i >= 0; i--) {
            data[i] = null;
        }
        size = 0;
    }

    //-----------------------------------------------------------------------
    /**
     * Converts input keys to another object for storage in the map.
     * This implementation masks nulls.
     * Subclasses can override this to perform alternate key conversions.
     * <p>
     * The reverse conversion can be changed, if required, by overriding the
     * getKey() method in the hash entry.
     * 
     * @param key  the key convert
     * @return the converted key
     */
    protected Object convertKey(Object key) {
        return (key == null ? NULL : key);
    }
    
    /**
     * Gets the hash code for the key specified.
     * This implementation uses the additional hashing routine from JDK1.4.
     * Subclasses can override this to return alternate hash codes.
     * 
     * @param key  the key to get a hash code for
     * @return the hash code
     */
    protected int hash(Object key) {
        // same as JDK 1.4
        int h = key.hashCode();
        h += ~(h << 9);
        h ^=  (h >>> 14);
        h +=  (h << 4);
        h ^=  (h >>> 10);
        return h;
    }
    
    /**
     * Compares two keys for equals.
     * This implementation uses the equals method.
     * Subclasses can override this to match differently.
     * 
     * @param key1  the first key to compare
     * @param key2  the second key to compare
     * @return true if equal
     */
    protected boolean isEqualKey(Object key1, Object key2) {
        return (key1 == key2 || key1.equals(key2));
    }
    
    /**
     * Compares two values for equals.
     * This implementation uses the equals method.
     * Subclasses can override this to match differently.
     * 
     * @param value1  the first value to compare
     * @param value2  the second value to compare
     * @return true if equal
     */
    protected boolean isEqualValue(Object value1, Object value2) {
        return (value1 == value2 || value1.equals(value2));
    }
    
    /**
     * Gets the index into the data storage for the hashCode specified.
     * This implementation uses the least significant bits of the hashCode.
     * Subclasses can override this to return alternate bucketing.
     * 
     * @param hashCode  the hash code to use
     * @param dataSize  the size of the data to pick a bucket from
     * @return the bucket index
     */
    protected int hashIndex(int hashCode, int dataSize) {
        return hashCode & (dataSize - 1);
    }
    
    //-----------------------------------------------------------------------
    /**
     * Gets the entry mapped to the key specified.
     * <p>
     * This method exists for subclasses that may need to perform a multi-step
     * process accessing the entry. The public methods in this class don't use this
     * method to gain a small performance boost.
     * 
     * @param key  the key
     * @return the entry, null if no match
     */
    protected HashEntry getEntry(Object key) {
        key = convertKey(key);
        int hashCode = hash(key);
        HashEntry entry = data[hashIndex(hashCode, data.length)]; // no local for hash index
        while (entry != null) {
            if (entry.hashCode == hashCode && isEqualKey(key, entry.key)) {
                return entry;
            }
            entry = entry.next;
        }
        return null;
    }

    //-----------------------------------------------------------------------
    /**
     * Updates an existing key-value mapping to change the value.
     * <p>
     * This implementation calls <code>setValue()</code> on the entry.
     * Subclasses could override to handle changes to the map.
     * 
     * @param entry  the entry to update
     * @param newValue  the new value to store
     */
    protected void updateEntry(HashEntry entry, Object newValue) {
        entry.setValue(newValue);
    }
    
    /**
     * Reuses an existing key-value mapping, storing completely new data.
     * <p>
     * This implementation sets all the data fields on the entry.
     * Subclasses could populate additional entry fields.
     * 
     * @param entry  the entry to update, not null
     * @param hashIndex  the index in the data array
     * @param hashCode  the hash code of the key to add
     * @param key  the key to add
     * @param value  the value to add
     */
    protected void reuseEntry(HashEntry entry, int hashIndex, int hashCode, Object key, Object value) {
        entry.next = data[hashIndex];
        entry.hashCode = hashCode;
        entry.key = key;
        entry.value = value;
    }
    
    //-----------------------------------------------------------------------
    /**
     * Adds a new key-value mapping into this map.
     * <p>
     * This implementation calls <code>createEntry()</code>, <code>addEntry()</code>
     * and <code>checkCapacity()</code>.
     * It also handles changes to <code>modCount</code> and <code>size</code>.
     * Subclasses could override to fully control adds to the map.
     * 
     * @param hashIndex  the index into the data array to store at
     * @param hashCode  the hash code of the key to add
     * @param key  the key to add
     * @param value  the value to add
     */
    protected void addMapping(int hashIndex, int hashCode, Object key, Object value) {
        modCount++;
        HashEntry entry = createEntry(data[hashIndex], hashCode, key, value);
        addEntry(entry, hashIndex);
        size++;
        checkCapacity();
    }
    
    /**
     * Creates an entry to store the key-value data.
     * <p>
     * This implementation creates a new HashEntry instance.
     * Subclasses can override this to return a different storage class,
     * or implement caching.
     * 
     * @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 HashEntry(next, hashCode, key, value);
    }
    
    /**
     * Adds an entry into this map.
     * <p>
     * This implementation adds the entry to the data storage table.
     * Subclasses could override to handle changes to the map.
     *
     * @param entry  the entry to add
     * @param hashIndex  the index into the data array to store at
     */
    protected void addEntry(HashEntry entry, int hashIndex) {
        data[hashIndex] = entry;
    }
    
    //-----------------------------------------------------------------------
    /**
     * Removes a mapping from the map.
     * <p>
     * This implementation calls <code>removeEntry()</code> and <code>destroyEntry()</code>.
     * It also handles changes to <code>modCount</code> and <code>size</code>.
     * Subclasses could override to fully control removals from the map.
     * 
     * @param entry  the entry to remove
     * @param hashIndex  the index into the data structure
     * @param previous  the previous entry in the chain
     */
    protected void removeMapping(HashEntry entry, int hashIndex, HashEntry previous) {
        modCount++;
        removeEntry(entry, hashIndex, previous);
        size--;
        destroyEntry(entry);
    }
    
    /**
     * Removes an entry from the chain stored in a particular index.
     * <p>
     * This implementation removes the entry from the data storage table.
     * The size is not updated.
     * Subclasses could override to handle changes to the map.
     * 
     * @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) {
        if (previous == null) {
            data[hashIndex] = entry.next;
        } else {
            previous.next = entry.next;
        }
    }
    
    /**
     * Kills an entry ready for the garbage collector.
     * <p>
     * This implementation prepares the HashEntry for garbage collection.
     * Subclasses can override this to implement caching (override clear as well).
     * 
     * @param entry  the entry to destroy
     */
    protected void destroyEntry(HashEntry entry) {
        entry.next = null;
        entry.key = null;
        entry.value = null;
    }
    
    //-----------------------------------------------------------------------
    /**
     * Checks the capacity of the map and enlarges it if necessary.
     * <p>
     * This implementation uses the threshold to check if the map needs enlarging
     */
    protected void checkCapacity() {
        if (size >= threshold) {
            ensureCapacity(data.length * 2);
        }
    }
    
    /**
     * Changes the size of the data structure to the capacity proposed.
     * 
     * @param newCapacity  the new capacity of the array
     */
    protected void ensureCapacity(int newCapacity) {
        int oldCapacity = data.length;
        if (newCapacity <= oldCapacity) {
            return;
        }
        HashEntry oldEntries[] = data;
        HashEntry newEntries[] = new HashEntry[newCapacity];

        modCount++;
        for (int i = oldCapacity - 1; i >= 0; i--) {
            HashEntry entry = oldEntries[i];
            if (entry != null) {
                oldEntries[i] = null;  // gc
                do {
                    HashEntry next = entry.next;
                    int index = hashIndex(entry.hashCode, newCapacity);  
                    entry.next = newEntries[index];
                    newEntries[index] = entry;
                    entry = next;
                } while (entry != null);
            }
        }
        threshold = calculateThreshold(newCapacity, loadFactor);
        data = newEntries;
    }

    /**
     * Calculates the new capacity of the map.
     * This implementation normalizes the capacity to a power of two.
     * 
     * @param proposedCapacity  the proposed capacity
     * @return the normalized new capacity
     */
    protected int calculateNewCapacity(int proposedCapacity) {
        int newCapacity = 1;
        if (proposedCapacity > MAXIMUM_CAPACITY) {
            newCapacity = MAXIMUM_CAPACITY;
        } else {
            while (newCapacity < proposedCapacity) {
                newCapacity <<= 1;  // multiply by two
            }
            if (proposedCapacity > MAXIMUM_CAPACITY) {
                newCapacity = MAXIMUM_CAPACITY;
            }
        }
        return newCapacity;
    }
    
    /**
     * Calculates the new threshold of the map, where it will be resized.
     * This implementation uses the load factor.
     * 
     * @param newCapacity  the new capacity
     * @param factor  the load factor
     * @return the new resize threshold
     */
    protected int calculateThreshold(int newCapacity, float factor) {
        return (int) (newCapacity * factor);
    }
    
    //-----------------------------------------------------------------------
    /**
     * 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.
     * It also avoids creating the Map.Entry object.
     * 
     * @return the map iterator
     */
    public MapIterator mapIterator() {
        if (size == 0) {
            return IteratorUtils.EMPTY_MAP_ITERATOR;
        }
        return new HashMapIterator(this);
    }

    /**
     * MapIterator implementation.
     */
    protected static class HashMapIterator extends HashIterator implements MapIterator {
        
        protected HashMapIterator(AbstractHashedMap parent) {
            super(parent);
        }

        public Object next() {
            return super.nextEntry().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);
        }
    }
    
    //-----------------------------------------------------------------------    
    /**
     * Gets the entrySet view of the map.
     * Changes made to the view affect this map.
     * The Map Entry is not an independent object and changes as the 
     * iterator progresses.
     * To simply iterate through the entries, use {@link #mapIterator()}.
     * 
     * @return the entrySet view
     */
    public Set entrySet() {
        if (entrySet == null) {
            entrySet = new EntrySet(this);
        }
        return entrySet;
    }
    
    /**
     * 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 IteratorUtils.EMPTY_ITERATOR;
        }
        return new EntrySetIterator(this);
    }

    /**
     * EntrySet implementation.
     */
    protected static class EntrySet extends AbstractSet {
        /** The parent map */
        protected final AbstractHashedMap parent;
        
        protected EntrySet(AbstractHashedMap parent) {
            super();
            this.parent = parent;
        }

        public int size() {
            return parent.size();
        }
        
        public void clear() {
            parent.clear();
        }
        
        public boolean contains(Object entry) {
            if (entry instanceof Map.Entry) {
                return parent.containsKey(((Map.Entry) entry).getKey());
            }
            return false;
        }
        
        public boolean remove(Object obj) {
            if (obj instanceof Map.Entry == false) {
                return false;
            }
            Map.Entry entry = (Map.Entry) obj;
            Object key = entry.getKey();
            boolean result = parent.containsKey(key);
            parent.remove(key);
            return result;
        }

        public Iterator iterator() {
            return parent.createEntrySetIterator();
        }
    }

    /**
     * EntrySet iterator.
     */
    protected static class EntrySetIterator extends HashIterator {
        
        protected EntrySetIterator(AbstractHashedMap parent) {
            super(parent);
        }

        public Object next() {
            return super.nextEntry();
        }
    }

    //-----------------------------------------------------------------------    
    /**
     * Gets the keySet view of the map.
     * Changes made to the view affect this map.
     * To simply iterate through the keys, use {@link #mapIterator()}.
     * 
     * @return the keySet view
     */
    public Set keySet() {
        if (keySet == null) {
            keySet = new KeySet(this);
        }
        return keySet;
    }

    /**
     * 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 IteratorUtils.EMPTY_ITERATOR;
        }
        return new KeySetIterator(this);
    }

    /**
     * KeySet implementation.
     */
    protected static class KeySet extends AbstractSet {
        /** The parent map */
        protected final AbstractHashedMap parent;
        
        protected KeySet(AbstractHashedMap parent) {
            super();
            this.parent = parent;
        }

        public int size() {
            return parent.size();
        }
        
        public void clear() {
            parent.clear();
        }
        
        public boolean contains(Object key) {
            return parent.containsKey(key);
        }
        
        public boolean remove(Object key) {
            boolean result = parent.containsKey(key);
            parent.remove(key);
            return result;
        }

        public Iterator iterator() {
            return parent.createKeySetIterator();
        }
    }

    /**
     * KeySet iterator.
     */
    protected static class KeySetIterator extends EntrySetIterator {
        
        protected KeySetIterator(AbstractHashedMap parent) {
            super(parent);
        }

        public Object next() {
            return super.nextEntry().getKey();
        }
    }
    
    //-----------------------------------------------------------------------    
    /**
     * Gets the values view of the map.
     * Changes made to the view affect this map.
     * To simply iterate through the values, use {@link #mapIterator()}.
     * 
     * @return the values view
     */
    public Collection values() {
        if (values == null) {
            values = new Values(this);
        }
        return values;
    }

    /**
     * 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 IteratorUtils.EMPTY_ITERATOR;
        }
        return new ValuesIterator(this);
    }

    /**
     * Values implementation.
     */
    protected static class Values extends AbstractCollection {
        /** The parent map */
        protected final AbstractHashedMap parent;
        
        protected Values(AbstractHashedMap parent) {
            super();
            this.parent = parent;
        }

        public int size() {
            return parent.size();
        }
        
        public void clear() {
            parent.clear();
        }
        
        public boolean contains(Object value) {
            return parent.containsValue(value);
        }
        
        public Iterator iterator() {
            return parent.createValuesIterator();
        }
    }

    /**
     * Values iterator.
     */
    protected static class ValuesIterator extends HashIterator {
        
        protected ValuesIterator(AbstractHashedMap parent) {
            super(parent);
        }

        public Object next() {
            return super.nextEntry().getValue();
        }
    }
    
    //-----------------------------------------------------------------------
    /**
     * HashEntry used to store the data
     */
    protected static class HashEntry implements Map.Entry, KeyValue {
        /** The next entry in the hash chain */
        protected HashEntry next;
        /** The hash code of the key */
        protected int hashCode;
        /** The key */
        protected Object key;
        /** The value */
        protected Object value;
        
        protected HashEntry(HashEntry next, int hashCode, Object key, Object value) {
            super();
            this.next = next;
            this.hashCode = hashCode;
            this.key = key;
            this.value = value;
        }
        
        public Object getKey() {
            return (key == NULL ? null : key);
        }
        
        public Object getValue() {
            return value;
        }
        
        public Object setValue(Object value) {
            Object old = this.value;
            this.value = value;
            return old;
        }
        
        public boolean equals(Object obj) {
            if (obj == this) {
                return true;
            }
            if (obj instanceof Map.Entry == false) {
                return false;
            }
            Map.Entry other = (Map.Entry) obj;
            return
                (getKey() == null ? other.getKey() == null : getKey().equals(other.getKey())) &&
                (getValue() == null ? other.getValue() == null : getValue().equals(other.getValue()));
        }
        
        public int hashCode() {
            return (getKey() == null ? 0 : getKey().hashCode()) ^
                   (getValue() == null ? 0 : getValue().hashCode()); 
        }
        
        public String toString() {
            return new StringBuffer().append(getKey()).append('=').append(getValue()).toString();
        }
    }
    
    /**
     * Base Iterator
     */
    protected static abstract class HashIterator implements Iterator {
        
        /** The parent map */
        protected final AbstractHashedMap parent;
        /** The current index into the array of buckets */
        protected int hashIndex;
        /** The last returned entry */
        protected HashEntry last;
        /** The next entry */
        protected HashEntry next;
        /** The modification count expected */
        protected int expectedModCount;
        
        protected HashIterator(AbstractHashedMap parent) {
            super();
            this.parent = parent;
            HashEntry[] data = parent.data;
            int i = data.length;
            HashEntry next = null;
            while (i > 0 && next == null) {
                next = data[--i];
            }
            this.next = next;
            this.hashIndex = i;
            this.expectedModCount = parent.modCount;
        }

        public boolean hasNext() {
            return (next != null);
        }

        protected HashEntry nextEntry() { 
            if (parent.modCount != expectedModCount) {
                throw new ConcurrentModificationException();
            }
            HashEntry newCurrent = next;
            if (newCurrent == null)  {
                throw new NoSuchElementException(AbstractHashedMap.NO_NEXT_ENTRY);
            }
            HashEntry[] data = parent.data;
            int i = hashIndex;
            HashEntry n = newCurrent.next;
            while (n == null && i > 0) {
                n = data[--i];
            }
            next = n;
            hashIndex = i;
            last = newCurrent;
            return newCurrent;
        }

        protected HashEntry 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 String toString() {
            if (last != null) {
                return "Iterator[" + last.getKey() + "=" + last.getValue() + "]";
            } else {
                return "Iterator[]";
            }
        }
    }
    
    //-----------------------------------------------------------------------
    /**
     * Writes the map data to the stream. This method must be overridden if a
     * subclass must be setup before <code>put()</code> is used.
     * <p>
     * Serialization is not one of the JDK's nicest topics. Normal serialization will
     * initialise the superclass before the subclass. Sometimes however, this isn't
     * what you want, as in this case the <code>put()</code> method on read can be
     * affected by subclass state.
     * <p>
     * The solution adopted here is to serialize the state data of this class in
     * this protected method. This method must be called by the
     * <code>writeObject()</code> of the first serializable subclass.
     * <p>
     * Subclasses may override if they have a specific field that must be present
     * on read before this implementation will work. Generally, the read determines
     * what must be serialized here, if anything.
     * 
     * @param out  the output stream
     */
    protected void doWriteObject(ObjectOutputStream out) throws IOException {
        out.writeFloat(loadFactor);
        out.writeInt(data.length);
        out.writeInt(size);
        for (MapIterator it = mapIterator(); it.hasNext();) {
            out.writeObject(it.next());
            out.writeObject(it.getValue());
        }
    }

    /**
     * Reads the map data from the stream. This method must be overridden if a
     * subclass must be setup before <code>put()</code> is used.
     * <p>
     * Serialization is not one of the JDK's nicest topics. Normal serialization will
     * initialise the superclass before the subclass. Sometimes however, this isn't
     * what you want, as in this case the <code>put()</code> method on read can be
     * affected by subclass state.
     * <p>
     * The solution adopted here is to deserialize the state data of this class in
     * this protected method. This method must be called by the
     * <code>readObject()</code> of the first serializable subclass.
     * <p>
     * Subclasses may override if the subclass has a specific field that must be present
     * before <code>put()</code> or <code>calculateThreshold()</code> will work correctly.
     * 
     * @param in  the input stream
     */
    protected void doReadObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
        loadFactor = in.readFloat();
        int capacity = in.readInt();
        int size = in.readInt();
        init();
        data = new HashEntry[capacity];
        for (int i = 0; i < size; i++) {
            Object key = in.readObject();
            Object value = in.readObject();
            put(key, value);
        }
        threshold = calculateThreshold(data.length, loadFactor);
    }
    
    //-----------------------------------------------------------------------
    /**
     * Clones the map without cloning the keys or values.
     * <p>
     * To implement <code>clone()</code>, a subclass must implement the
     * <code>Cloneable</code> interface and make this method public.
     *
     * @return a shallow clone
     */
    protected Object clone() {
        try {
            AbstractHashedMap cloned = (AbstractHashedMap) super.clone();
            cloned.data = new HashEntry[data.length];
            cloned.entrySet = null;
            cloned.keySet = null;
            cloned.values = null;
            cloned.modCount = 0;
            cloned.size = 0;
            init();
            cloned.putAll(this);
            return cloned;
            
        } catch (CloneNotSupportedException ex) {
            return null;  // should never happen
        }
    }
    
    /**
     * Compares this map with another.
     * 
     * @param obj  the object to compare to
     * @return true if equal
     */
    public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        }
        if (obj instanceof Map == false) {
            return false;
        }
        Map map = (Map) obj;
        if (map.size() != size()) {
            return false;
        }
        MapIterator it = mapIterator();
        try {
            while (it.hasNext()) {
                Object key = it.next();
                Object value = it.getValue();
                if (value == null) {
                    if (map.get(key) != null || map.containsKey(key) == false) {
                        return false;
                    }
                } else {
                    if (value.equals(map.get(key)) == false) {
                        return false;
                    }
                }
            }
        } catch (ClassCastException ignored)   {
            return false;
        } catch (NullPointerException ignored) {
            return false;
        }
        return true;
    }

    /**
     * Gets the standard Map hashCode.
     * 
     * @return the hash code defined in the Map interface
     */
    public int hashCode() {
        int total = 0;
        Iterator it = createEntrySetIterator();
        while (it.hasNext()) {
            total += it.next().hashCode();
        }
        return total;
    }

    /**
     * Gets the map as a String.
     * 
     * @return a string version of the map
     */
    public String toString() {
        if (size() == 0) {
            return "{}";
        }
        StringBuffer buf = new StringBuffer(32 * size());
        buf.append('{');

        MapIterator it = mapIterator();
        boolean hasNext = it.hasNext();
        while (hasNext) {
            Object key = it.next();
            Object value = it.getValue();
            buf.append(key == this ? "(this Map)" : key)
               .append('=')
               .append(value == this ? "(this Map)" : value);

            hasNext = it.hasNext();
            if (hasNext) {
                buf.append(',').append(' ');
            }
        }

        buf.append('}');
        return buf.toString();
    }
}
