The short answer is don't mix object types in a list like that
. You can only store objects of different class types if you store them as an Object, which means you can only retrieve them as an Object, so you're very limited as to what you can do with them.
It is possible to use the Reflection API to discover the real type of the object you want to use, then cast it to that type to use it. I strongly advise against this, it should be the last resort when there is no alternative.
There are far better alternatives, but it depends on exactly what you're trying to achieve. The ideal situation is to store a class type that has the methods that you want to use. This is usually done by defining an interface with the methods you want and having various classes implement the methods in their own way. Then the list can be specified to store the interface type and all classes that implement the interface can be used with it.