public static boolean isFunction(Class type) {
        if (type.isInterface()) {
            String typeName = type.getName();
            if (typeName.startsWith("java.util.function.")) {
                return true;
            }

            return type.isAnnotationPresent(FunctionalInterface.class);
        }

        return false;
    }
decimal is integer, check has non-zero small

@param decimal
@return
core/src/main/java/com/alibaba/fastjson2/util/TypeUtils.java