final Map<TypeVariable<?>, Type> map = GenericsUtil.getTypeVariableMap(Hoge.class);
        final Method method = Hoge.class.getMethod("map");
        assertThat(GenericsUtil.getActualKeyClassOfMap(method.getGenericReturnType(), map), is(sameClass(String.class)));
    }

    /**
     * @throws Exception
     */
    public void testGetActualValueClassOfMap() throws Exception {

     * @param map
     *            the map that contains the type variables and type arguments
     * @return the actual key type of the map, or null if not a parameterized map
     */
    public static Class<?> getActualKeyClassOfMap(final Type type, final Map<TypeVariable<?>, Type> map) {
        if (!isTypeOf(type, Map.class)) {
            return null;
        }
        return getActualClass(getGenericParameter(type, 0), map);
    }