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Re: e==null? really?

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Eric Sosman wrote:
> markspace wrote:
> > bob smith wrote:
> >> Is it possible to do this in Java?
> >>
> >> throw null;
> >
> >
> > Yes. JLS:
> >
> > <http://docs.oracle.com/javase/specs/jls/se7/html/jls-14.html#jls-14.18>
> >
> >
> > "throw Expression ;
> >
> > The Expression in a throw statement must denote either 1) a variable or
> > value of a reference type which is assignable (§5.2) to the type
> > Throwable, or 2) the null reference..."
> 
>      Interesting. Reading onward, though, we find
> 
> 	"If evaluation of the Expression completes normally,
> 	producing a null value, then an instance V' of class
> 	NullPointerException is created and thrown instead of
> 	null. [...]"
> 
> ... which leaves a bit of a mystery.  The O.P.'s example was
> (fleshed out somewhat)

No mystery. The first refers to a compiler rule, the second to a runtime rule.

> 	try {
> 	    throw null;
> 	} catch (Exception e) {
> 	    // e is null here!
> 	}
> 
> ... but according to the JLS that shouldn't have happened.  Bug?

It's no more a bug than that you might get a 'ClassCastException' when you cast
a value to another type. The compiler allows what the runtime sometimes 
doesn't.

-- 
Lew

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Thread

e==null?  really? bob smith <bob@coolfone.comze.com> - 2012-07-13 07:18 -0700
  Re: e==null?  really? markspace <-@.> - 2012-07-13 07:29 -0700
    Re: e==null?  really? Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-13 10:48 -0400
      Re: e==null?  really? markspace <-@.> - 2012-07-13 08:22 -0700
        Re: e==null?  really? Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-07-13 09:35 -0700
      Re: e==null?  really? Lew <lewbloch@gmail.com> - 2012-07-13 13:11 -0700
        Re: e==null?  really? Joerg Meier <joergmmeier@arcor.de> - 2012-07-13 22:55 +0200
          Re: e==null?  really? "javax.swing.JSnarker" <gharriman@boojum.mit.edu> - 2012-07-13 17:01 -0400
    Re: e==null?  really? Lew <lewbloch@gmail.com> - 2012-07-13 13:09 -0700
  Re: e==null?  really? Roedy Green <see_website@mindprod.com.invalid> - 2012-07-13 12:09 -0700
    Re: e==null?  really? Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-07-13 23:06 +0200
      Re: e==null?  really? Roedy Green <see_website@mindprod.com.invalid> - 2012-07-14 06:30 -0700

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