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Groups > comp.lang.java.programmer > #2649

Re: Enums: Properties vs. Methods

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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.

> 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.

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

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.

-- 
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg

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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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