Groups > comp.lang.java.programmer > #39959

Re: switch is shared declaration

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From	Arne Vajhøj <arne@vajhoej.dk>
Newsgroups	comp.lang.java.programmer
Subject	Re: switch is shared declaration
Date	Sun, 28 May 2023 13:42:22 -0400
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On 5/28/2023 9:16 AM, Marcel Mueller wrote:
> Am 28.05.23 um 14:36 schrieb Eric Sosman:
>> On 5/28/2023 7:31 AM, Marcel Mueller wrote:
>>> Shouldn't this be a problem too because the 2nd switch label bypasses 
>>> the initialization of s?
>>
>> The `case 1:' part *is* the initialization of `s'.  There is a
>> *declaration* of `s' in the `case -1:' part, but the declaration
>> does nothing (here) to initialize the `s' reference.
>>
>> If we added another case to the switch, say
>>
>>      default:
>>          System.out.println(s);
>>          break;
>>
>> ... the compiler would complain that `s' might be used without
>> being initialized, true.   But the code as shown does not try
>> to retrieve any value from `s', so the compiler holds its peace.
> 
> So ist is only valid because of the optimization?

Not a traditional optimization.

The check if things used are guaranteed to be initialized
just do not apply.

>    String s;
> is a default constructor call.

No. s is just a reference not pointing to any object.

>    s = "1";
> is an assignment operator call.

An assignment.

> I expected the latter to be invalid without the first (unless String is 
> a trivial type).

You can not assign to a variable not declared no matter whether
it is simple or not. But I suspect that was not what you meant.


String s;
s = "1";

is sort of equivalent to C:

char *s;
s = "1";

Arne

Thread

switch is shared declaration "e.d.pro...@gmail.com" <e.d.programmer@gmail.com> - 2023-05-24 05:15 -0700
  Re: switch is shared declaration Arne Vajhøj <arne@vajhoej.dk> - 2023-05-24 12:57 -0400
    Re: switch is shared declaration Arne Vajhøj <arne@vajhoej.dk> - 2023-05-24 13:16 -0400
    Re: switch is shared declaration "e.d.pro...@gmail.com" <e.d.programmer@gmail.com> - 2023-05-24 11:05 -0700
      Re: switch is shared declaration Michael Jung <miju@golem.phantasia.org> - 2023-05-28 12:57 +0200
  Re: switch is shared declaration Marcel Mueller <news.5.maazl@spamgourmet.org> - 2023-05-28 13:31 +0200
    Re: switch is shared declaration Eric Sosman <esosman@comcast-dot-net.invalid> - 2023-05-28 08:36 -0400
      Re: switch is shared declaration Marcel Mueller <news.5.maazl@spamgourmet.org> - 2023-05-28 15:16 +0200
        Re: switch is shared declaration Arne Vajhøj <arne@vajhoej.dk> - 2023-05-28 13:42 -0400
      Re: switch is shared declaration Arne Vajhøj <arne@vajhoej.dk> - 2023-05-28 13:43 -0400

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