Subversion Repositories mkgmap

/*
 * Copyright (C) 2015 Gerd Petermann
 *
 * 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.LinkedHashSet;
import java.util.Set;


public class MultiHashSet<K,V> extends HashMap<K,Set<V>> {

        /**
        * the empty set to be returned when there is key without values.
        */
        private final Set<V> emptyList = Collections.emptySet();

        /**
        * 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.
        */
        public Set<V> get(Object key) {
                Set<V> result = super.get(key);
                return result == null ? emptyList : result;
        }


        public boolean add(K key, V value ) {
                Set<V> values = super.get(key);
            if (values == null ) {
                values = new LinkedHashSet<V>();
                super.put( key, values );
            }
            return values.add(value);
        }

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

            boolean existed = values.remove(value);
               
                if (values.isEmpty())
                        super.remove(key);

                return existed;
        }
}