Subversion Repositories mkgmap

/*
 * Copyright (C) 2013.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 3 or
 * version 2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 */

package uk.me.parabola.util;

import java.util.Collections;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;


public class MultiHashMap<K,V> extends HashMap<K,List<V>> {

        /**
        * Returns the list of values associated with the given key.
        *
        * @param key the key to get the values for.
        * @return a list of values for the given keys or the empty list of no such
        *         value exist.
        */
        @Override
        public List<V> get(Object key) {
                List<V> result = super.get(key);
                return result == null ? Collections.emptyList() : result;
        }

        /**
         * Add mapping for the given key and value.
         * If the key already exists, the value is added to the end of the existing list.
         *
         * @param key the key
         * @param value the value
         * @return the value
         */
        public V add(K key, V value ) {
                super.computeIfAbsent(key, k -> new LinkedList<>()).add(value);
                return value;  
        }

        public V removeMapping(K key, V value) {
                List<V> values = super.get(key);
                if (values == null)
                        return null;

                values.remove(value);

                if (values.isEmpty())
                        super.remove(key);

                return value;
        }
}