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Re: Java generics and type erasure

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In article <irlega$3kp$1@news.albasani.net>, Lew <noone@lewscanon.com> 
wrote:

> On 05/26/2011 04:34 AM, Esmond Pitt wrote:
> > On 26/05/2011 4:48 PM, Lawrence D'Oliveiro wrote:
> >>> No -- presumably, it would have caused problems compiling 1.4 source code
> >>> against 1.5's libraries, not running existing 1.4 bytecode linked to 1.5
> >>> libraries.
> >>
> >> In Java terms, what’s the difference?
> >
> > The difference is that generic type-signatures are present in 
> > .class files for compilation purposes even though generics are 
> > erased to their lower bounds at runtime, so that the compiler can 
> > enforce the semantics of generics.
> 
> This contradicts the statement that Ian Shef made upthread that type 
> erasure occurs in compilation.

I don't see a contradiction. Since 1.5, the compiler puts Type and 
GenericDeclaration information in the class file for access via 
reflection, as shown using javap; but the information is not otherwise 
used at runtime.

> It seems I was correct after all, and that it really does happen at 
> runtime.

I'm still not seeing a disparity. The compiler interprets generic 
declarations and stores them in the class file. At runtime, those types 
are available to introspection but not checked for validity, a job 
already done at compile time.

As you observed earlier, the problem is more subtle than my initial 
response. I welcome any clarification.

-- 
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>

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Thread

Java generics and type erasure Marcin Pietraszek <m.pietraszek@gmail.com> - 2011-05-23 13:18 -0700
  Re: Java generics and type erasure "John B. Matthews" <nospam@nospam.invalid> - 2011-05-23 22:54 -0400
    Re: Java generics and type erasure Lew <noone@lewscanon.com> - 2011-05-24 01:45 -0400
      Re: Java generics and type erasure Marcin Pietraszek <m.pietraszek@gmail.com> - 2011-05-24 12:39 -0700
      Re: Java generics and type erasure Ian Shef <invalid@avoiding.spam> - 2011-05-24 20:04 +0000
        Re: Java generics and type erasure Lew <noone@lewscanon.com> - 2011-05-24 17:06 -0400
          Re: Java generics and type erasure Ian Shef <invalid@avoiding.spam> - 2011-05-24 23:05 +0000
            Re: Java generics and type erasure Susan Calvin <s.calvin@usr.invalid> - 2011-05-25 00:13 +0000
              Re: Java generics and type erasure Lawrence D'Oliveiro <ldo@geek-central.gen.new_zealand> - 2011-05-26 10:18 +1200
                Re: Java generics and type erasure Susan Calvin <s.calvin@usr.invalid> - 2011-05-26 01:12 +0000
                Re: Java generics and type erasure Lawrence D'Oliveiro <ldo@geek-central.gen.new_zealand> - 2011-05-26 13:59 +1200
                Re: Java generics and type erasure Susan Calvin <s.calvin@usr.invalid> - 2011-05-26 04:18 +0000
                Re: Java generics and type erasure Lawrence D'Oliveiro <ldo@geek-central.gen.new_zealand> - 2011-05-26 18:48 +1200
                Re: Java generics and type erasure Esmond Pitt <esmond.pitt@bigpond.com> - 2011-05-26 18:34 +1000
                Re: Java generics and type erasure Lew <noone@lewscanon.com> - 2011-05-26 07:45 -0400
                Re: Java generics and type erasure "John B. Matthews" <nospam@nospam.invalid> - 2011-05-26 15:25 -0400
                Re: Java generics and type erasure Esmond Pitt <esmond.pitt@bigpond.com> - 2011-05-27 12:01 +1000
                Re: Java generics and type erasure Lew <noone@lewscanon.com> - 2011-05-26 22:15 -0400
                Re: Java generics and type erasure Esmond Pitt <esmond.pitt@bigpond.com> - 2011-05-27 13:04 +1000
                Re: Java generics and type erasure Lew <noone@lewscanon.com> - 2011-05-27 01:27 -0400
                Re: Java generics and type erasure Esmond Pitt <esmond.pitt@bigpond.com> - 2011-05-27 18:07 +1000
                Re: Java generics and type erasure Lew <noone@lewscanon.com> - 2011-05-27 10:18 -0400
                Re: Java generics and type erasure Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-05-27 17:03 +0000
                Re: Java generics and type erasure Lew <noone@lewscanon.com> - 2011-05-27 13:27 -0400
                Re: Java generics and type erasure Esmond Pitt <esmond.pitt@bigpond.com> - 2011-05-30 15:19 +1000
                Re: Java generics and type erasure Tom McGlynn <taqmcg@gmail.com> - 2011-05-26 19:53 -0700
                Re: Java generics and type erasure Lew <noone@lewscanon.com> - 2011-05-27 01:30 -0400
                Re: Java generics and type erasure Esmond Pitt <esmond.pitt@bigpond.com> - 2011-05-27 18:09 +1000
                Re: Java generics and type erasure Lew <noone@lewscanon.com> - 2011-05-27 10:22 -0400
                Re: Java generics and type erasure Esmond Pitt <esmond.pitt@bigpond.com> - 2011-05-30 15:23 +1000
                Re: Java generics and type erasure Lew <noone@lewscanon.com> - 2011-05-30 02:35 -0400

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