Where and when to use generics?

Question

I'm brushing up on Java 5.0, I'm at 'generics' - I always hated c++ templates and knew they would catch up with me sooner or later...
I have a fairly simple question about where and how to use them, conceptually.
Am I correct in thinking that they are primarily concerned with items contained within a class and passed to a class?
I'm trying to find a useful bit of code to write to practice with them and I've been half tempted to re-write something that uses lots of inheritance simply because I know the code in question needed a lot of casting, but my gut feeling is that generics doesn't have an awful lot to do with inheritance and re-jigging a class that relied on inheritance to use generics is barking up the wrong tree.
I'd really appreciate some informed comments before I go trundling off down a path that is going to end with reams of pointless code.
Thanks,
Steve

Answer 1

IMO the most useful feature of using Generics is compile time typesafety.
Consider the pre-1.5 code for making a LinkedList that contains strings:
LinkedList l = new LinkedList();
l.add("Hello world!");
l.add(new Integer(100));    // <---- runtime exceptionInstead, you can now write the code like this:
LinkedList<String> l = new LinkedList<String>();
l.add("Hello world!");
l.add(new Integer(100));    // compile time exceptionIf you accidentally put the wrong type in a Collection you will get a nice compile time exception instead of a ClassCastException at runtime.