How are Java generics different from C++ templates? Why can't I use int as a parameter?

Question

I am trying to create

ArrayList myList = new ArrayList();

in Java but that does not work.

Can someone explain

Answer 1

The reason that int doesn't work, is that you cannot use primitive types as generic parameters in Java.

As to your actual question, how C++ templates are different from Java generics, the answer is that they're really, really different. The languages essentially apply completely different approaches to implementing a similar end effect.

Java tends to focus on the definition of the generic. That is, the validity of the generic definition is checked by only considering the code in the generic. If parameters are not properly constrained, certain actions cannot be performed on them. The actual type it's eventually invoked with, is not considered.

C++ is the opposite. Only minimal verification is done on the template itself. It really only needs to be parsable to be considered valid. The actual correctness of the definition is done at the place in which the template is used.