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Groups > comp.lang.java.programmer > #2657

Re: Enums: Properties vs. Methods

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On 31 Mrz., 14:41, Lew <no...@lewscanon.com> wrote:
> Robert Klemme wrote:
> > Lew<l...@lewscanon.com>  wrote:
> >> Yes.  So?  that's what HotSpot does, except it's not one per instance,
> >> it's N>= 1 per instance, potentially.  HotSpot optimizes for
> >> individual hot spots in the code, hence the name.
>
> > Hmm... Considering
>
> > public void hotSpotMethod(Valve v) {
> >    // code
> >    if (v.isOpen()) {
> >      // ...
> >    }
> >    else {
> >      // ...
> >    }
> >    // more code
> > }
>
> > Since this method can be invoked with different Valve instances the
> > only optimization I can see so far is
>
> > public void hotSpotMethod(Valve v) {
> >    // code
> >    if (v.open) {
> >      // ...
> >    }
> >    else {
> >      // ...
> >    }
> >    // more code
> > }
>
> > or are you saying that we can actually get this?
>
> I make no claims whatsoever about individually crafted examples designed to
> show where HotSpot might fail.  I only repeat publicly available information
> about what it does.

These examples were not crafted to show where HotSpot fails but to
learn what kind of optimizations you had in mind.  I went from

http://www.oracle.com/technetwork/java/javase/tech/index-jsp-136373.html

and found

http://www.oracle.com/technetwork/java/whitepaper-135217.html#method
http://www.oracle.com/technetwork/java/whitepaper-135217.html#optimizations

which does not give away too much.  There's also

http://en.wikipedia.org/wiki/Java_performance

But that did not provide too much insight either.

http://www.google.de/search?q=java+hotspot+optimizations

Wasn't too good either.  What public resources did you have in mind?

> > public void hotSpotMethod(boolean valve_open) {
> >    // code
> >    if (valve_open) {
> >      // ...
> >    }
> >    else {
> >      // ...
> >    }
> >    // more code
> > }
> ...
> >> Yes, it wins, but that has nothing to do with memory or performance in
> >> the JVM.
>
> >> For the toy example given I would expect no difference, since the
> >> final variables ocmpile to constants anyway.
> > But those final variables are only constant /per instance/.  How would
> > hotspot be able to inline them?
>
> Per instance, or perhaps per call.  Of course.  It might then un-inline them
> for a later call, then re-inline them - even the exact same call if conditions
> change that affect optimization.

Yes, but frankly, that's too general for me.  Can you be more specific
with regard to the current case we are discussing?

> The beauty of HotSpot is that it accounts for changing run-time circumstances,
> so it can perform optimizations that elude static analysis.

Certainly.

> You should read about it.
>
> ...
>
> >> As for JVM effects, I would expect the two approaches to be
> >> indistinguishable.  Constant variables are compiled into constants in
> >> the code, so they get treated identically with constants (being, after
> >> all, constants in truth) at run time.
> > I don't think these final members (which are not static!) can be
> > compiled into the code because there is just one class (and hence one
> > instance of each method) but multiple instances with different sets of
> > values for their final members.
>
> The JLS requires them to be compiled into the code.  And regardless of what
> you don't think, that's exactly what happens.  You should read about it.
>
> Start here:  JLS, §17.5.3, as I cited earlier.

It seems that is not a good place to start (see other postings). :-)

Cheers

robert

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Enums: Properties vs. Methods Robert Klemme <shortcutter@googlemail.com> - 2011-03-29 08:18 -0700
  Re: Enums: Properties vs. Methods Lew <noone@lewscanon.com> - 2011-03-29 11:47 -0400
    Re: Enums: Properties vs. Methods Robert Klemme <shortcutter@googlemail.com> - 2011-03-30 20:00 +0200
      Re: Enums: Properties vs. Methods Lew <lew@lewscanon.com> - 2011-03-30 13:17 -0700
        Re: Enums: Properties vs. Methods Robert Klemme <shortcutter@googlemail.com> - 2011-03-31 00:48 -0700
          Re: Enums: Properties vs. Methods Lew <noone@lewscanon.com> - 2011-03-31 08:41 -0400
            Re: Enums: Properties vs. Methods Robert Klemme <shortcutter@googlemail.com> - 2011-03-31 08:26 -0700
              Re: Enums: Properties vs. Methods Lew <noone@lewscanon.com> - 2011-03-31 22:16 -0400
                Re: Enums: Properties vs. Methods Robert Klemme <shortcutter@googlemail.com> - 2011-04-02 11:56 +0200
                Re: Enums: Properties vs. Methods Lew <noone@lewscanon.com> - 2011-04-02 10:29 -0400
                Re: Enums: Properties vs. Methods Robert Klemme <shortcutter@googlemail.com> - 2011-04-03 13:14 +0200
  Re: Enums: Properties vs. Methods markspace <-@.> - 2011-03-29 09:26 -0700
    Re: Enums: Properties vs. Methods Robert Klemme <shortcutter@googlemail.com> - 2011-03-30 20:06 +0200
      Re: Enums: Properties vs. Methods markspace <-@.> - 2011-03-30 12:40 -0700
        Re: Enums: Properties vs. Methods Robert Klemme <shortcutter@googlemail.com> - 2011-03-31 00:38 -0700
  Re: Enums: Properties vs. Methods Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-03-29 19:03 +0200
    Re: Enums: Properties vs. Methods Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-03-29 19:04 +0200
  Re: Enums: Properties vs. Methods Roedy Green <see_website@mindprod.com.invalid> - 2011-03-29 12:49 -0700
  Re: Enums: Properties vs. Methods Roedy Green <see_website@mindprod.com.invalid> - 2011-03-29 12:52 -0700
    Re: Enums: Properties vs. Methods Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-03-29 22:45 +0200
      Re: Enums: Properties vs. Methods Lew <noone@lewscanon.com> - 2011-03-29 17:08 -0400
        Re: Enums: Properties vs. Methods Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-03-29 23:25 +0200
          Re: Enums: Properties vs. Methods Lew <noone@lewscanon.com> - 2011-03-29 19:05 -0400
            Re: Enums: Properties vs. Methods Lew <noone@lewscanon.com> - 2011-03-29 19:40 -0400
              Re: Enums: Properties vs. Methods Robert Klemme <shortcutter@googlemail.com> - 2011-03-31 02:57 -0700
                Re: Enums: Properties vs. Methods Lew <noone@lewscanon.com> - 2011-03-31 08:52 -0400
                Re: Enums: Properties vs. Methods Lew <noone@lewscanon.com> - 2011-03-31 08:54 -0400
            Re: Enums: Properties vs. Methods Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-03-30 18:40 +0200
              Re: Enums: Properties vs. Methods Lew <lew@lewscanon.com> - 2011-03-30 10:33 -0700
                Re: Enums: Properties vs. Methods Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-03-30 20:43 +0200
                Re: Enums: Properties vs. Methods Lew <lew@lewscanon.com> - 2011-03-30 13:20 -0700
                Re: Enums: Properties vs. Methods Lew <noone@lewscanon.com> - 2011-03-31 08:55 -0400
  Re: Enums: Properties vs. Methods Wanja Gayk <brixomatic@yahoo.com> - 2011-04-02 11:23 +0200
    Re: Enums: Properties vs. Methods Lew <noone@lewscanon.com> - 2011-04-02 10:36 -0400
      Re: Enums: Properties vs. Methods Wanja Gayk <brixomatic@yahoo.com> - 2011-04-02 21:20 +0200

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