multihashmap.java

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        } else {
            for (Iterator it = map.entrySet().iterator(); it.hasNext();) {
                Map.Entry entry = (Map.Entry) it.next();
                put(entry.getKey(), entry.getValue());
            }
        }
    }

    /**
     * Adds a collection of values to the collection associated with the specified key.
     *
     * @param key  the key to store against
     * @param values  the values to add to the collection at the key, null ignored
     * @return true if this map changed
     * @since Commons Collections 3.1
     */    
    public boolean putAll(Object key, Collection values) {
        if (values == null || values.size() == 0) {
            return false;
        }
        Collection coll = getCollection(key);
        if (coll == null) {
            coll = createCollection(values);
            if (coll.size() == 0) {
                return false;
            }
            super.put(key, coll);
            return true;
        } else {
            return coll.addAll(values);
        }
    }

    /**
     * Checks whether the map contains the value specified.
     * <p>
     * This checks all collections against all keys for the value, and thus could be slow.
     * 
     * @param value  the value to search for
     * @return true if the map contains the value
     */
    public boolean containsValue(Object value) {
        Set pairs = super.entrySet();

        if (pairs == null) {
            return false;
        }
        Iterator pairsIterator = pairs.iterator();
        while (pairsIterator.hasNext()) {
            Map.Entry keyValuePair = (Map.Entry) pairsIterator.next();
            Collection coll = (Collection) keyValuePair.getValue();
            if (coll.contains(value)) {
                return true;
            }
        }
        return false;
    }

    /**
     * Checks whether the collection at the specified key contains the value.
     * 
     * @param value  the value to search for
     * @return true if the map contains the value
     * @since Commons Collections 3.1
     */
    public boolean containsValue(Object key, Object value) {
        Collection coll = getCollection(key);
        if (coll == null) {
            return false;
        }
        return coll.contains(value);
    }

    /**
     * Removes a specific value from map.
     * <p>
     * The item is removed from the collection mapped to the specified key.
     * Other values attached to that key are unaffected.
     * <p>
     * If the last value for a key is removed, <code>null</code> will be returned
     * from a subsequant <code>get(key)</code>.
     * 
     * @param key  the key to remove from
     * @param item  the value to remove
     * @return the value removed (which was passed in), null if nothing removed
     */
    public Object remove(Object key, Object item) {
        Collection valuesForKey = getCollection(key);
        if (valuesForKey == null) {
            return null;
        }
        boolean removed = valuesForKey.remove(item);
        if (removed == false) {
            return null;
        }
        // remove the list if it is now empty
        // (saves space, and allows equals to work)
        if (valuesForKey.isEmpty()){
            remove(key);
        }
        return item;
    }

    /**
     * Clear the map.
     * <p>
     * This clears each collection in the map, and so may be slow.
     */
    public void clear() {
        // For gc, clear each list in the map
        Set pairs = super.entrySet();
        Iterator pairsIterator = pairs.iterator();
        while (pairsIterator.hasNext()) {
            Map.Entry keyValuePair = (Map.Entry) pairsIterator.next();
            Collection coll = (Collection) keyValuePair.getValue();
            coll.clear();
        }
        super.clear();
    }

    /**
     * Gets a collection containing all the values in the map.
     * <p>
     * This returns a collection containing the combination of values from all keys.
     *
     * @return a collection view of the values contained in this map
     */
    public Collection values() {
        Collection vs = values;
        return (vs != null ? vs : (values = new Values()));
    }

    /**
     * Gets the values iterator from the superclass, as used by inner class.
     *
     * @return iterator
     */
    Iterator superValuesIterator() {
        return super.values().iterator();
    }

    //-----------------------------------------------------------------------
    /**
     * Inner class to view the elements.
     */
    private class Values extends AbstractCollection {

        public Iterator iterator() {
            return new ValueIterator();
        }

        public int size() {
            int compt = 0;
            Iterator it = iterator();
            while (it.hasNext()) {
                it.next();
                compt++;
            }
            return compt;
        }

        public void clear() {
            MultiHashMap.this.clear();
        }

    }

    /**
     * Inner iterator to view the elements.
     */
    private class ValueIterator implements Iterator {
        private Iterator backedIterator;
        private Iterator tempIterator;

        private ValueIterator() {
            backedIterator = MultiHashMap.this.superValuesIterator();
        }

        private boolean searchNextIterator() {
            while (tempIterator == null || tempIterator.hasNext() == false) {
                if (backedIterator.hasNext() == false) {
                    return false;
                }
                tempIterator = ((Collection) backedIterator.next()).iterator();
            }
            return true;
        }

        public boolean hasNext() {
            return searchNextIterator();
        }

        public Object next() {
            if (searchNextIterator() == false) {
                throw new NoSuchElementException();
            }
            return tempIterator.next();
        }

        public void remove() {
            if (tempIterator == null) {
                throw new IllegalStateException();
            }
            tempIterator.remove();
        }

    }

    //-----------------------------------------------------------------------
    /**
     * Clones the map creating an independent copy.
     * <p>
     * The clone will shallow clone the collections as well as the map.
     * 
     * @return the cloned map
     */
    public Object clone() {
        MultiHashMap cloned = (MultiHashMap) super.clone();

        // clone each Collection container
        for (Iterator it = cloned.entrySet().iterator(); it.hasNext();) {
            Map.Entry entry = (Map.Entry) it.next();
            Collection coll = (Collection) entry.getValue();
            Collection newColl = createCollection(coll);
            entry.setValue(newColl);
        }
        return cloned;
    }

    /** 
     * Creates a new instance of the map value Collection container.
     * <p>
     * This method can be overridden to use your own collection type.
     *
     * @param coll  the collection to copy, may be null
     * @return the new collection
     */
    protected Collection createCollection(Collection coll) {
        if (coll == null) {
            return new ArrayList();
        } else {
            return new ArrayList(coll);
        }
    }

}