TypedMap.java

    abstract class TypedMap {

        private Map internalMap = new HashMap();

        public <T> TypedMap put(Class<T> k, List<T> v) {
            internalMap.put(k, v);
            return this;
        }

        public <T> List<T> get(Class<T> k) {
            return (List<T>) internalMap.get(k);
        }

        public <T> T getSingleValue(Class<T> k) {
            List<T> l = (List<T>) internalMap.get(k);
            if (l == null)
                return null;
            if (l.size() == 1)
                return l.get(0);
            else
                throw new IllegalStateException("More than one value");
        }
    }