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Groups > comp.lang.java.programmer > #11713

Re: Converting Sets

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On 2/2/12 5:32 AM, Roedy Green wrote:
> On Thu, 02 Feb 2012 12:47:58 +0100, Mayeul<mayeul.marguet@free.fr>
> wrote, quoted or indirectly quoted someone who said :
>
>> Conversion of a Set<X>  to a Set<? extends Y>, ensuring the Set contains
>> objects assignable to Y, but no new elements can be added to it:
>>
>> Set<X>  setOfX = obtainSetOfX();
>> Set<? extends Y>  setOfY = setOfX;
>
> This what I was looking for , that did not require an element by
> element copy.
> Ah, but this this you created is NOT a Set<Y>.  You cannot add
> arbirary Y to it, just more X. I feel queasy. How could the compiler
> keep track that setOfY could only contain X.
It does not. Instead, it prevents you from any add operation which 
requires the type.

In other words, setOfY becomes somewhat "read-only" for typed 
operations. You can still clear it, or sub-sets of it, but you can no 
longer add *any* object to it, whatever type.

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Thread

Converting Sets Roedy Green <see_website@mindprod.com.invalid> - 2012-02-01 23:34 -0800
  Re: Converting Sets Mayeul <mayeul.marguet@free.fr> - 2012-02-02 12:47 +0100
    Re: Converting Sets Roedy Green <see_website@mindprod.com.invalid> - 2012-02-02 05:32 -0800
      Re: Converting Sets Mayeul <mayeul.marguet@free.fr> - 2012-02-02 16:06 +0100
        Re: Converting Sets markspace <-@.> - 2012-02-02 09:21 -0800
          Re: Converting Sets Jim Janney <jjanney@shell.xmission.com> - 2012-02-02 13:13 -0700
            Re: Converting Sets markspace <-@.> - 2012-02-02 13:46 -0800
          Re: Converting Sets Roedy Green <see_website@mindprod.com.invalid> - 2012-02-02 16:29 -0800
            Re: Converting Sets Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-02-02 17:34 -0800
              Re: Converting Sets Arne Vajhøj <arne@vajhoej.dk> - 2012-02-04 20:49 -0500
                Re: Converting Sets Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-02-06 12:55 -0800
                Re: Converting Sets Arne Vajhøj <arne@vajhoej.dk> - 2012-02-06 20:47 -0500
                Re: Converting Sets Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-02-06 17:51 -0800
                Re: Converting Sets Arne Vajhøj <arne@vajhoej.dk> - 2012-02-06 20:57 -0500
            Re: Converting Sets markspace <-@.> - 2012-02-03 14:12 -0800
              Re: Converting Sets Lew <lewbloch@gmail.com> - 2012-02-03 22:32 -0800
            Re: Converting Sets Lew <lewbloch@gmail.com> - 2012-02-03 22:30 -0800
          Re: Converting Sets Lew <lewbloch@gmail.com> - 2012-02-03 22:33 -0800
      Re: Converting Sets Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-02-02 11:02 -0800
    Re: Converting Sets Roedy Green <see_website@mindprod.com.invalid> - 2012-02-02 18:25 -0800
      Re: Converting Sets markspace <-@.> - 2012-02-03 14:25 -0800

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