Sort of. You can effectively do so in a language like Java, which allows you to inspect the types of objects at runtime. For example if you have a class `Foo` with two subclasses `SubA` and `SubB` you could do something like this:

    public static void test(Foo f) {
        if (f isinstanceof SubA) {
            SubA a = (SubA)f;
            /* ... */
        } else if (f isinstanceof SubB) {
            SubB b = (SubB)f;
        }
    }

This works okay but you have to implement all the machinery yourself, and for a statically typed language Java is notoriously type-unsafe so if you make a mistake with your casts you're basically not going to find out until you get an exception at runtime. And of course there might be other existing subclasses of `Foo` which means that you get no compile-time guarantee that you didn't miss a possible case.

Standard ML approaches subtyping in a very different way that renders this kind of approach impossible. It gives you less freedom in that it eliminates downcasting, but that ultimately results in a safer language. Of course Standard ML has proper sum types with all of their compile-time guarantees so there's little reason for it anyway.