Parsing a superclass object to subclass object dynamicly

I have about 20 different classes that extend a superclass. Each subclass has some methods that are not implemented in the superclass.
At runtime I need to parse the superclass object to whatever subclass object for my program to work correctly. How do I do this?

Manually I would do something like

Superclass super = method.getSomething();
Subclass sub = (Subclass)super;

This works fine, but I don't know how to do this at runtime because don't know which class that it is to be parsed. Any ideas?

thanks in advance

EDIT: I mean casting obviously.

You can use instanceof to check the type of an object and then cast it from there.

I don't think you have the best design for your app. I'm not good at OOP.
The different logic required for each subclass should probably be in the subclass.
Or you should use an interface so that all the subclasses have the same type.
Or ...