For the first one, you should get some sort of error ( ArrayList<type> and ArrayList are two different types); my guess is that the pre-processor fixes this for you. The second one should work normally, as ArrayList extends List. The only problem is that you will have to cast to an ArrayList whenever you want to use an ArrayList-specific method.

Thanks calsign, you wrote ArrayList<item>. Isn't <type> correct? ;)

Yes, sorry. My bad. type is simply a generic type used to show any given type, no? Fixing my response anyway...

I think so, i was really checking, cause some times just get things wrong. :-)

As said, the first form should generate a warning with a real Java compiler. I don't think Processing fixes that, but just hides simple warnings to avoid distracting users: they want against possible mistakes but doesn't prevent compilation to be achieved.

The second form is often used. You declare a generic kind of list, and select one possible implementation (ArrayList) to fulfill the task. You can then easily substitute another implementation (eg. LinkedList) without disturbing the whole program.
It works well as long as you use only the methods declared in List (that's an interface), which are generally enough for most current needs. But indeed, if you need some specific method of ArrayList or of another implementation, you have to cast the List to the specific type.

The first actually i found by mistake, just forgot and later realised and the stuff was working fine ;)

I missed the important stuff...

Call a List to an ArrayList? I'm not entirely sure what you mean.

You can define a List and initialize an ArrayList, as you have demonstrated:

1. List<type> happy = new ArrayList<type>();

And you can cast that List to an ArrayList in order to access ArrayList-specific functions:

1. ((ArrayList) happy).add(new type());
   

Sorry, i meant cast in previous post. My question is answered by your second answer.