[jdom-interest] NoSuch*Exceptions in JDOM

[Jools Enticknap]

On Sun, 18 Jun 2000, Jason Hunter wrote:

> You know, I was halfway into proposing such a method when I stopped to
> give it some more thought.  It lets you write code
> 
> if (elt.hasChild("foo")) {
>   Element child = elt.getChild("foo");
> }
> else {
>   // deal with none
> }
> 
> which is debatably better to read.  The reason I wanted to think more
> about it was that hasChild() would have to do an O(n) scan through the
> children, then getChild() would have to do the same scan.  Course, we
> could cache the hasChild() child trusting the user is pretty likely to
> call getChild() if it returns true, but that's another piece of memory
> every Element will have to hold.

During my initial thought, prior to writing my initial post I wondered
about this, but after refreshing myself with the code I realized that in
the success case it would be 2 O(n) scans through the children which I
thought was a bit heavy, although caching would resolve that as long as
no add/delete/has Child calls to another Element name were made prior to
getChild being called.

But to me this all seems like a large hammer on a small nail, lets take
the above example and nullify it.

Element e = elem.getChild("foo");
if ( e != null ) {
	// Do something with e
}
else {
	// Do something else.
}

Looks like it does the same, but with much less overhead. 

Don't get me wrong, I'm not shooting the hasChild() call down, I think
it's a good idea, and I like the ability to check on the presence of a
child before I try to get it, it's just that I think if we want to make it
efficient caching is required, much like what has been done with
getContent(). 

But it all adds weight to what is a nicely lightweight XML implementation
which already does what is required.

<suggestion>

1) Drop the NoSuch*Exceptions.
2) Return nulls, when the 'thing' you were looking for is not there.
3) Add the hasChild() call for those who don't want to check for null, but
   add a JavaDoc comment stating the overhead of using this instead of 
   null.

Adding the hasChild is a no-brainer, gets rid of the Exception and
returning null helps the CPU restricted people get the job done quicker
:-)

</suggestion>

--Jools (who's now off the fence)