Re: Aspect questions?
Novice wrote:
And I need to look at List
<E>
and ArrayList
<E>
in more detail too. I've already
glanced at them and expect to start a thread on Interfaces [sic] soon so that I
can hash out some of my conceptions and misconceptions about interfaces
vs. classes. It might take a couple of days because I've got some other
things that I need to do first....
I favor a style of programming I call "type-based programming" that relies on
interfaces and generics.
Since you say you write comments first, this should be natural for you.
An interface is like a compilable comment that specifies what classes are
supposed to accomplish. Classes are specific implementations of what their
interfaces promise.
In general, per the advice of /Effective Java/ (2nd ed.) by Joshua Bloch* and
other wise people, you should declare variables, return types, etc., as the
most general (closest to interface) type that promises what you need.
If all your list needs is what's promised by 'List<E>', you declare the type
as the interface type. If it needs additional methods or attributes declared
by 'ArrayList<E>' but not in the interface, you use the more specific type. If
you don't even need the "listiness" but just that it's a collection, declare
the type 'Collection<E>'.
When you design a program, design it in terms of interfaces. Defer
implementations as far as makes sense. This lets you focus on _what_ the
program should do rather than _how_.
I frequently write interfaces even when I'm only writing one implementing class.
So taking lists as the example:
List<String> options = new ArrayList<>();
I declared the 'options' variable as a 'List<String>', not as an
'ArrayList<String>'. If I discover that the array-backed list wasn't giving me
the performance or other implementation-specific behavior I need, but a linked
list does, I can refactor more easily:
List<String> options = new LinkedList<>();
The rest of the program, depending only on the "list"ness and not the
"array"ness, is unharmed.
(What performance differences are there? Excellent question! Pop quiz - please
answer this post with your answer - where would you find out about performance
characteristics of 'ArrayList<E>' and 'LinkedList<E>'?)
Summary:
Interface: what to do
Class: how to do it
--
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg