Re: Java blunders

Eric Sosman <esosman@comcast-dot-net.invalid>
Fri, 25 Jul 2014 08:35:55 -0400
On 7/25/2014 12:07 AM, thinbluernime wrote:

On Wed, 23 Jul 2014 15:14:34 -0400, Eric Sosman wrote:

      IMHO Java would be a better language if `switch' were removed
altogether, fall-through or not. But that's just MHO, which (clearly)
is not widely shared. Meanwhile, I oppose anything that encourages the
use of the construct.

If Java existed in a vacuum, so one could always use polymorphism instead
of "switch", then maybe. But Java does not exist in a vacuum and at the
edge it will often be necessary to take a finite set of numbers, strings,
or something such as a png compression-type magic number, an enum-like
field from a database, or similar and react to that. And that is a place
where switch is useful and polymorphism isn't. Switch can even be used to
turn "which value was received" to "which class to instantiate" so you
can use polymorphism in the rest of the code.

     Sure. I use `switch' myself, now and then. But I find that I use
it less frequently in Java than in other languages, that there's simply
less need for it. (Also, I've more than once reconsidered a `switch'
I'd written, and jettisoned it in favor of something else.) Sure, the
construct is occasionally useful, but it's far from crucial. I don't
think it is fruitful to over-ornament the language to encourage the use
of a rarely-applicable construct.

     By the way, have you taken a look at the byte code generated by
`switch' on String values? Ye flippin' gods! It compiles into *two*
`switch' statements, one sparse and one dense, sort of like

    int _case_;
    switch (string.hashCode()) {
    case "A".hashCode():
        if ("A".equals(string)) _case_ = 1; else _case_ = 0;
    case "B".hashCode():
        if ("B".equals(string)) _case_ = 2; else _case_ = 0;
        _case_ = 0;
    switch (_case_) {
    case 1:
        /* "A" stuff */
    case 2:
        /* "B" stuff */
    case 0:
        /* default stuff */

Something like this would be necessary if any of the cases' hashCode()s
collided *and* the cases ran different code *and* there was fall-through
involved, but absent even one of these the compiler ought to be able to
generate something less cumbersome. Even a smarter compiler, though,
would still have to compute hashCode() on the switch'ed String unless
it decided to abandon the `switch'-style strategy altogether.


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