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Groups > comp.lang.java.programmer > #15387

Re: "Small" Program Challenge.

From Lew <lewbloch@gmail.com>
Newsgroups comp.lang.java.programmer
Subject Re: "Small" Program Challenge.
Date 2012-06-18 12:47 -0700
Organization http://groups.google.com
Message-ID <20ad5d23-f0a7-4926-9d99-b9dc0a7ea18e@googlegroups.com> (permalink)
References (4 earlier) <4fde76ce$0$287$14726298@news.sunsite.dk> <jrlu9c$eab$2@speranza.aioe.org> <IqxDr.28704$hJ3.24051@newsfe14.iad> <jrmaju$u48$1@news.albasani.net> <jrmbpg$6ik$1@speranza.aioe.org>

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On Sunday, June 17, 2012 9:45:34 PM UTC-7, javax.swing.JSnarker wrote:
> On 18/06/2012 12:25 AM, Lew wrote:
> > You aren't supposed to rely on a bug.
> 
> It's not a bug.
> 
> > The JLS 3rd ed., which covers Java 5 and Java 6, says,
> > "A Java virtual machine starts up by loading a specified class and then
> > invoking the method main in this specified class."
> 
> Exactly. It loads the specified class, as part of which that class's 
> static initializer runs. And if it's an enum, the enum elements' 
> initializers run too.

Loading does not imply initialization, and in fact cannot.

The JVM is forbidden to initialize a class except under specific 
circumstances, a
> 
> If one of those calls System.exit(0) you could argue, theoretically, 
> that there's an ambiguity in what the spec says should be the behavior. 
> On the one hand, System.exit(0) should terminate the running VM instance 
> when invoked. On the other hand, that precludes "and then invoking the 
> method main in this specified class".
> 
> However, the observed behavior seems to be out of spec. The main 
> method's absence should prompt an error upon the attempt to invoke it, 
> and did. The error being generated before the main method should be 
> being invoked is dissimilar from any other JVM behavior. For example, if 
> you create code that attempts to invoke Foo.quux() by reflection, and 
> there's no quux static method in class Foo, there won't be any error 
> until the reflection attempt, which will throw an exception when it occurs.
> 
> More generally, "and then invoking the method main" can mean one of two 
> things, given that main itself is static: the call to main is statically 
> compiled in, in which case javac should complain when compiling the call 
> site, or the call to main is reflective, in which case the error should 
> not occur until runtime and should not occur until the running code 
> reaches the location of the reflective invocation. We're now seeing an 
> error later than compile time and earlier than the running code reaches 
> the location of the reflective invocation, which behavior is 
> inconsistent with *each* static-method call semantic.
> 
> -- 
> public final class JSnarker
> extends JComponent
> A JSnarker is an NNTP-aware component that asynchronously provides 
> snarky output when the Ego.needsPuncturing() event is fired in cljp.



On Sunday, June 17, 2012 9:45:34 PM UTC-7, javax.swing.JSnarker wrote:
> On 18/06/2012 12:25 AM, Lew wrote:
> > You aren't supposed to rely on a bug.
> 
> It's not a bug.
> 
> > The JLS 3rd ed., which covers Java 5 and Java 6, says,
> > "A Java virtual machine starts up by loading a specified class and then
> > invoking the method main in this specified class."
> 
> Exactly. It loads the specified class, as part of which that class's 
> static initializer runs. And if it's an enum, the enum elements' 
> initializers run too.
> 
> If one of those calls System.exit(0) you could argue, theoretically, 
> that there's an ambiguity in what the spec says should be the behavior. 
> On the one hand, System.exit(0) should terminate the running VM instance 
> when invoked. On the other hand, that precludes "and then invoking the 
> method main in this specified class".
> 
> However, the observed behavior seems to be out of spec. The main 
> method's absence should prompt an error upon the attempt to invoke it, 
> and did. The error being generated before the main method should be 
> being invoked is dissimilar from any other JVM behavior. For example, if 
> you create code that attempts to invoke Foo.quux() by reflection, and 
> there's no quux static method in class Foo, there won't be any error 
> until the reflection attempt, which will throw an exception when it occurs.
> 
> More generally, "and then invoking the method main" can mean one of two 
> things, given that main itself is static: the call to main is statically 
> compiled in, in which case javac should complain when compiling the call 
> site, or the call to main is reflective, in which case the error should 
> not occur until runtime and should not occur until the running code 
> reaches the location of the reflective invocation. We're now seeing an 
> error later than compile time and earlier than the running code reaches 
> the location of the reflective invocation, which behavior is 
> inconsistent with *each* static-method call semantic.
> 
> -- 
> public final class JSnarker
> extends JComponent
> A JSnarker is an NNTP-aware component that asynchronously provides 
> snarky output when the Ego.needsPuncturing() event is fired in cljp.



On Sunday, June 17, 2012 9:45:34 PM UTC-7, javax.swing.JSnarker wrote:
> On 18/06/2012 12:25 AM, Lew wrote:
> > You aren't supposed to rely on a bug.
> 
> It's not a bug.
> 
> > The JLS 3rd ed., which covers Java 5 and Java 6, says,
> > "A Java virtual machine starts up by loading a specified class and then
> > invoking the method main in this specified class."
> 
> Exactly. It loads the specified class, as part of which that class's 
> static initializer runs. And if it's an enum, the enum elements' 
> initializers run too.

Not true. Loading does not imply initialization, and in fact is forbidden to.

The initializers only run under specific circumstances, separately from 
loading.

I have cited the relevant JLS sections.

> If one of those calls System.exit(0) you could argue, theoretically, 
> that there's an ambiguity in what the spec says should be the behavior. 
> On the one hand, System.exit(0) should terminate the running VM instance 
> when invoked. On the other hand, that precludes "and then invoking the 
> method main in this specified class".

False premise, unreliable conclusion. Loading does not imply initialization.

> However, the observed behavior seems to be out of spec. The main 
> method's absence should prompt an error upon the attempt to invoke it, 

Indeed.

-- 
Lew

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Thread

"Small" Program Challenge. Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-06-13 13:45 -0700
  Re: "Small" Program Challenge. Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-06-13 13:52 -0700
    Re: "Small" Program Challenge. Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-06-13 16:17 -0700
      Re: "Small" Program Challenge. glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-06-14 00:16 +0000
    Re: "Small" Program Challenge. Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-06-13 16:19 -0700
      Re: "Small" Program Challenge. Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-06-13 16:24 -0700
    Re: "Small" Program Challenge. markspace <-@.> - 2012-06-13 17:40 -0700
  Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-13 21:28 -0400
  Re: "Small" Program Challenge. Roedy Green <see_website@mindprod.com.invalid> - 2012-06-13 20:52 -0700
    Re: "Small" Program Challenge. "Hiram Hunt" <hiramhunt@verizon.net> - 2012-06-14 08:23 -0400
      Re: "Small" Program Challenge. "Hiram Hunt" <hiramhunt@verizon.net> - 2012-06-14 08:30 -0400
    Re: "Small" Program Challenge. Arne Vajhøj <arne@vajhoej.dk> - 2012-06-17 21:17 -0400
  Re: "Small" Program Challenge. Paul Cager <paul.cager@googlemail.com> - 2012-06-14 02:32 -0700
  Re: "Small" Program Challenge. Bent C Dalager <bcd@pvv.ntnu.no> - 2012-06-14 11:29 +0000
  Re: "Small" Program Challenge. Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-06-14 12:50 -0700
  Re: "Small" Program Challenge. Leif Roar Moldskred <leifm@dimnakorr.com> - 2012-06-14 15:49 -0500
  Re: "Small" Program Challenge. Gene Wirchenko <genew@ocis.net> - 2012-06-14 14:56 -0700
  Re: "Small" Program Challenge. Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-06-14 17:02 -0700
  Re: "Small" Program Challenge. Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-06-14 17:09 -0700
  Re: "Small" Program Challenge. Kevin McMurtrie <mcmurtrie@pixelmemory.us> - 2012-06-15 22:13 -0700
    Re: "Small" Program Challenge. Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-06-16 12:11 -0700
  Re: "Small" Program Challenge. Wanja Gayk <brixomatic@yahoo.com> - 2012-06-17 15:22 +0200
    Re: "Small" Program Challenge. Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-06-17 15:24 -0700
      Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-17 18:25 -0400
        Re: "Small" Program Challenge. Arne Vajhøj <arne@vajhoej.dk> - 2012-06-17 20:31 -0400
          Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-17 20:55 -0400
            Re: "Small" Program Challenge. Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-06-17 20:40 -0700
              Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-17 23:43 -0400
              Re: "Small" Program Challenge. Lew <noone@lewscanon.com> - 2012-06-17 21:25 -0700
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-18 00:45 -0400
                Re: "Small" Program Challenge. Lew <lewbloch@gmail.com> - 2012-06-18 12:47 -0700
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-18 15:57 -0400
                Re: "Small" Program Challenge. Lew <lewbloch@gmail.com> - 2012-06-18 13:31 -0700
                Re: "Small" Program Challenge. Leif Roar Moldskred <leifm@dimnakorr.com> - 2012-06-18 16:05 -0500
                Re: "Small" Program Challenge. Lew <lewbloch@gmail.com> - 2012-06-18 14:18 -0700
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-18 19:50 -0400
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-18 19:48 -0400
                Re: "Small" Program Challenge. David Lamb <dalamb@cs.queensu.ca> - 2012-06-19 08:07 -0400
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-19 15:26 -0400
                Re: "Small" Program Challenge. Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-06-18 09:04 -0700
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-18 13:09 -0400
                Re: "Small" Program Challenge. markspace <-@.> - 2012-06-18 11:06 -0700
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-18 14:46 -0400
                Re: "Small" Program Challenge. markspace <-@.> - 2012-06-18 13:22 -0700
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-18 19:51 -0400
                Re: "Small" Program Challenge. Wanja Gayk <brixomatic@yahoo.com> - 2012-06-20 13:11 +0200
                Re: "Small" Program Challenge. Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-06-22 12:54 -0700
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-22 18:30 -0400
                Re: "Small" Program Challenge. Lew <lewbloch@gmail.com> - 2012-06-25 12:59 -0700
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-25 16:49 -0400
                Re: "Small" Program Challenge. Lew <lewbloch@gmail.com> - 2012-06-18 12:44 -0700
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-18 16:01 -0400
                Re: "Small" Program Challenge. Lew <lewbloch@gmail.com> - 2012-06-18 13:36 -0700
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-18 20:01 -0400
                Re: "Small" Program Challenge. Lew <lewbloch@gmail.com> - 2012-06-18 18:25 -0700
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-18 22:01 -0400
                Re: "Small" Program Challenge. Gene Wirchenko <genew@ocis.net> - 2012-06-18 19:04 -0700
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-18 22:12 -0400
                Re: "Small" Program Challenge. Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-06-19 12:36 +0000
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-19 15:28 -0400
                Re: "Small" Program Challenge. Gene Wirchenko <genew@ocis.net> - 2012-06-19 09:12 -0700
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-19 15:30 -0400
                Re: "Small" Program Challenge. Gene Wirchenko <genew@ocis.net> - 2012-06-19 15:04 -0700
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-19 18:23 -0400
                Re: "Small" Program Challenge. Gene Wirchenko <genew@ocis.net> - 2012-06-19 15:32 -0700
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-19 19:09 -0400
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-19 19:10 -0400
                Re: "Small" Program Challenge. Lew <lewbloch@gmail.com> - 2012-06-19 17:19 -0700
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-19 20:42 -0400
                Re: "Small" Program Challenge. Leif Roar Moldskred <leifm@dimnakorr.com> - 2012-06-19 20:01 -0500
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-19 21:12 -0400
                Re: "Small" Program Challenge. Leif Roar Moldskred <leifm@dimnakorr.com> - 2012-06-19 20:32 -0500
                Re: "Small" Program Challenge. Lew <noone@lewscanon.com> - 2012-06-19 22:01 -0700
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-20 21:15 -0400
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-20 21:05 -0400
                Re: "Small" Program Challenge. Wanja Gayk <brixomatic@yahoo.com> - 2012-06-23 13:42 +0200
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-23 12:12 -0400
                Re: "Small" Program Challenge. Wanja Gayk <brixomatic@yahoo.com> - 2012-06-23 23:10 +0200
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-23 17:14 -0400
                Re: "Small" Program Challenge. Lew <noone@lewscanon.com> - 2012-06-19 22:15 -0700
                Re: "Small" Program Challenge. Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-06-20 10:34 +0000
                Re: "Small" Program Challenge. Lew <lewbloch@gmail.com> - 2012-06-20 10:45 -0700
                Re: "Small" Program Challenge. Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-06-21 08:13 +0000
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-21 17:18 -0400
                Re: "Small" Program Challenge. Lew <lewbloch@gmail.com> - 2012-06-21 15:30 -0700
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-21 20:28 -0400
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-20 21:22 -0400
                Re: "Small" Program Challenge. "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-06-20 21:19 -0400

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