Re: the java assert mechanism: is it useful?
Tom Anderson wrote:
On Mon, 4 Aug 2008, Arne Vajh?j wrote:
Tom Anderson wrote:
On Mon, 4 Aug 2008, marlow.andrew@googlemail.com wrote:
So do people actually find the java assert mechanism useful? I am
relatively new to java and have not seen it used in any projects I
have been on yet. But I do see lots of advice telling newcomers to
use it and how good it is. Does anyone here prefer to always have
the checking on?
I haven't ever used it.
I think the way to think of java assertions is as tiny unit tests
which are embedded in the application code.
There is a difference in that assertion can be used to test on stuff
that is not exposed to the outside.
Quite true.
The unit test addict would respond that there should never be stuff that
isn't exposed so that the test system can reach it - designing for
testability is a pillar of unit test dogma.
I don't think that is applicable.
You unit test for the contract that the class exposes.
You do not unit test the internals of the implementation.
Assertions can be used for the internals stuff.
It'd be nice if you could write assertions at class rather than
method level, and have them evaluated, say, every time a method on an
object of that class was called. Like:
public class OldMoney {
private int pounds ; // must be >= 0
assert pounds >= 0 ;
private int shillings ; // must be >=0, <20
assert (shillings >= 0) && (shillings < 20) ;
private int pence ; // must be >=0, <12
assert (pence >= 0) && (pence < 12) ;
}
The compiler would deal with them in a similar manner to field
initializer expressions - collect them together and invisibly prepend
them to every method body. Or perhaps the end of every method body.
Or both. Who knows.
Then you will need some type of AOP. If the values tested are exposed,
then it should be easy. If they are internal you will need a very
advanced AOP framework.
I was just thinking that the compiler would do it. No aspect funkiness
required.
The compiler will do it if you write the code everywhere.
But to write something once and get it applied to all methods
will bring it over in the AOP area.
Arne