Generic Epiphany - an Angled bracket vision

The past few days I have been looking at a lot of Generic code, reading articles about generics, looking at more generics code, snacking on generic code and washing it down with a nice generic drink and finally going to bed and dreaming about ...yes of course Generics.

I have been reading all sorts of stupid examples about putting apples and pears into a fruitbasket and how the Doctors class is using generics to check the different animals but of course you can't just put a dog or elephant into an animal class oh no.

I have blogged about Generics a fair bit, here is the last effort and it goes back through the others if you want a generic frenzy of information

http://hoskinator.blogspot.com/2006/08/type-safe-collections-generics-arent.html

I have kept plugging away with Generics and I have a decent grasp of it but one thing that I always had to double check was the placment of the angled brackets. Even copying out examples to play around with the code, I would often put the angled brackets in the wrong place. Anyway I was typing in an example and then all of a sudden, the angled brackets suddenly made sense, just like that, boom. It was a like a magic eye picture had suddenly come into view or when you look at the picture of the young woman looking one way and then suddenly realise that it can also be an old woman (if you have seen the picture you know what I mean, if not you probably think I'm mad)

I understand the bit inside the angled brackets is the "type" but I often got slightly confused with the talk of the base type and then then the type but it's actually not as difficult as people talking about it seem to make out.

I have found it's often easy to look at Generic code and reverse it (mentally) to non generic code and then see what you have got.

so you have this

List<String> myList = new ArrayList<String>();

becomes

List myList = new ArrayList();

look at it this way helped me understand how Generics worked more clearly and simplified the angled bracket placing conundrum I had been experiencing. It also help me understand the base class they were talking about e.g. List and ArrayList (List is the Base class and ArrayList is the subclass).

Looking at it now it seems fairly obvious and probably is to a lot of people out there but I now understand the angled brackets need to go anywhere where you are mentioning a class/object you are going to use e.g. List, ArrayList etc. so now I see the above

so this

List<String> myList = new ArrayList<String>();

I now see

base class type Variable name = new subclass class type ()

but I find it helpful to take this code back to the non generic style to understand what is going on
List myList = new ArrayList();

Obviously this is an easy example and it can get very complex but here is another example

A method example taking in an ArrayList

public List<String> changeStrings(ArrayList<String> s) { }

to this:

public List changeStrings(ArrayList s) { }

Once again it seems easier to imagine the pre generic code show first and then adding it in to see what is actually happening in the code.

I just thought I would share my Generic breakthrough on the blog in case anyone else was having a few problems with Generics, it's definitly one of the tricky sections on the SCJP exam I think.