Generics make your code more flexible and easier to read, and they help you avoid ClassCastExceptions at runtime. Get started with this introduction to using generics with the Java Collections ...

Certain principles hold for the use of iterators: In general, you should be able to have multiple traversals in progress at the same time; that is, an iterator should allow for the concept of nested ...

Almost every article or lecture about generics touches on collections and shows how to build a Stack<T>. Collections and stack building are an obvious choice, but generics have many other uses.

Apache Collections supports generics, so that's not a reason to choose one over the other. If the collections you need are available in it, I'd probably lean towards Guava, though.