Groups > comp.lang.java.programmer > #2922

Re: calling own methods from constructor

From	Tobias Blass <tobiasblass@gmx.net>
Newsgroups	comp.lang.java.programmer
Subject	Re: calling own methods from constructor
Date	2011-04-07 10:58 +0000
Organization	A noiseless patient Spider
Message-ID	<ink5cn$e78$1@dont-email.me> (permalink)
References	<slrnippkd9.phi.avl@gamma.logic.tuwien.ac.at> <2011040622233261380-angrybaldguy@gmailcom> <slrnipr02k.phi.avl@gamma.logic.tuwien.ac.at>

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On 2011-04-07, Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> wrote:
> Owen Jacobson <angrybaldguy@gmail.com> wrote:
>> On 2011-04-06 16:48:41 -0400, Andreas Leitgeb said:
>>
>>> There is well-known danger in calling own methods from the
>>> constructor, namely that the method called may be overridden
>>> by a subclass, which is really instanciated, but whose specific
>>> constructor has not yet been run.
>>> 
>>> I do not intend to delve into the details of static, private
>>> or final methods, or final'ity of the class itself (and maybe
>>> others) avoiding these problems, but instead I'm curious, why
>>> Java just doesn't simply forbid the dangerous calls.
>>
>> It's hard to prove that a constructor never calls a virtual method. Consider:
>> [ example of c'tor calling a private method "internalInit", which in turn
>>   calls virtual "virtualMethod". ]
>
> Good point. The compiler couldn't (at least not statically) prevent
> indirect calling of overridable non-static methods.
>
> But otoh., it refuses to compile this:
>   String bad = (String) new Integer(42);
> while allowing this: (sure bomb at runtime)
>   String bad = (String) (Object) new Integer(42);
>
> So, not being able to prevent something happening indirectly,
> doesn't imply that the direct way would need to be allowed, too.
>
> So, it boils down to the original question of whether there is also
> a good use of constructors (directly or indirectly) invoking
> overridable virtual methods.
>
> What it "good"? I have no exact definition, but if one of the 
> Java gurus (Brian Goetz, Joshua Bloch, James Gosling,...) ever
> before suggested a pattern that would involve it, then chances
> are good, that I'd accept it. Also, if the JSL or one of the big
> Java-based projects used it. Tom's example (Library) didn't
> convince me so far.
>
Why should it complain about your second example? You tell the Compiler
explicitly "Please consider this Integer as Object and this Object as String,
I know types don't match but I know what I'm doing" (I'm programming in C at
the moment where the Compiler doesn't complain about things javac wouldn't
even compile as in your first example, so YMMV)

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calling own methods from constructor Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-04-06 20:48 +0000
  Re: calling own methods from constructor Tom Anderson <twic@urchin.earth.li> - 2011-04-06 23:06 +0100
    Re: calling own methods from constructor Lew <noone@lewscanon.com> - 2011-04-06 18:24 -0400
      Re: calling own methods from constructor Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-04-07 08:44 +0000
        Re: calling own methods from constructor Robert Klemme <shortcutter@googlemail.com> - 2011-04-07 04:14 -0700
          Re: calling own methods from constructor Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-04-07 12:32 +0000
            Re: calling own methods from constructor Robert Klemme <shortcutter@googlemail.com> - 2011-04-07 05:55 -0700
            Re: calling own methods from constructor Lew <lew@lewscanon.com> - 2011-04-07 08:10 -0700
              Re: calling own methods from constructor Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-04-07 20:31 +0000
                Re: calling own methods from constructor Lew <lew@lewscanon.com> - 2011-04-07 14:10 -0700
                Re: calling own methods from constructor Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-04-07 22:15 +0000
                Re: calling own methods from constructor Lew <noone@lewscanon.com> - 2011-04-07 21:22 -0400
              Re: calling own methods from constructor Tom Anderson <twic@urchin.earth.li> - 2011-04-07 23:08 +0100
                Re: calling own methods from constructor Lew <noone@lewscanon.com> - 2011-04-07 21:24 -0400
                Re: calling own methods from constructor "Mike Schilling" <mscottschilling@hotmail.com> - 2011-04-09 22:06 -0700
            Re: calling own methods from constructor Tom Anderson <twic@urchin.earth.li> - 2011-04-07 23:10 +0100
              Re: calling own methods from constructor Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-04-07 22:24 +0000
        Re: calling own methods from constructor Lew <noone@lewscanon.com> - 2011-04-07 07:19 -0400
          Re: calling own methods from constructor Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-04-07 12:24 +0000
    Re: calling own methods from constructor Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-04-06 20:46 -0400
    Re: calling own methods from constructor Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-04-07 08:36 +0000
      Re: calling own methods from constructor Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-04-07 07:16 -0300
        Re: calling own methods from constructor Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-04-07 11:26 +0000
      Re: calling own methods from constructor Paul Cager <paul.cager@googlemail.com> - 2011-04-07 03:20 -0700
        Re: calling own methods from constructor Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-04-07 11:36 +0000
  Re: calling own methods from constructor Owen Jacobson <angrybaldguy@gmail.com> - 2011-04-06 22:23 -0400
    Re: calling own methods from constructor Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-04-07 09:13 +0000
      Re: calling own methods from constructor Tobias Blass <tobiasblass@gmx.net> - 2011-04-07 10:58 +0000
        Re: calling own methods from constructor Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-04-07 12:19 +0000
          Re: calling own methods from constructor Alessio Stalla <alessiostalla@gmail.com> - 2011-04-07 10:40 -0700
            Re: calling own methods from constructor Tobias Blass <tobiasblass@gmx.net> - 2011-04-07 19:00 +0000
              Re: calling own methods from constructor Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-04-07 20:11 +0000
              Re: calling own methods from constructor Jim Janney <jjanney@shell.xmission.com> - 2011-04-07 14:36 -0600
              Re: calling own methods from constructor Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-04-07 20:59 -0400
    Re: calling own methods from constructor Jim Janney <jjanney@shell.xmission.com> - 2011-04-07 10:26 -0600
      Re: calling own methods from constructor Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-04-07 20:16 +0000
      Re: calling own methods from constructor Lew <lew@lewscanon.com> - 2011-04-07 14:05 -0700
        Re: calling own methods from constructor Jim Janney <jjanney@shell.xmission.com> - 2011-04-07 16:15 -0600
          Re: calling own methods from constructor Lew <noone@lewscanon.com> - 2011-04-07 21:28 -0400
          Re: calling own methods from constructor Owen Jacobson <angrybaldguy@gmail.com> - 2011-04-07 23:21 -0400
            Re: calling own methods from constructor Owen Jacobson <angrybaldguy@gmail.com> - 2011-04-07 23:39 -0400
            Re: calling own methods from constructor Owen Jacobson <angrybaldguy@gmail.com> - 2011-04-07 23:58 -0400
            Re: calling own methods from constructor Tom Anderson <twic@urchin.earth.li> - 2011-04-08 20:32 +0100
      Re: calling own methods from constructor Tom Anderson <twic@urchin.earth.li> - 2011-04-07 23:05 +0100
        Re: calling own methods from constructor Jim Janney <jjanney@shell.xmission.com> - 2011-04-07 17:38 -0600
  Re: calling own methods from constructor Roedy Green <see_website@mindprod.com.invalid> - 2011-04-07 03:20 -0700
    Re: calling own methods from constructor Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-04-07 11:32 +0000
  Re: calling own methods from constructor Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-04-08 01:51 +0200
    Re: calling own methods from constructor Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-04-08 01:56 +0200
      Re: calling own methods from constructor Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-04-08 09:30 +0000
        Re: calling own methods from constructor Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-04-08 20:02 +0200

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