Path: csiph.com!news.swapon.de!eternal-september.org!feeder.eternal-september.org!mx02.eternal-september.org!.POSTED!not-for-mail
From: Mike Amling <mamling@chaff.us>
Newsgroups: comp.lang.java.programmer
Subject: Re: about class dependancies
Date: Mon, 21 Dec 2015 08:29:12 -0600
Organization: A noiseless patient Spider
Lines: 33
Message-ID: <n59255$6ve$1@dont-email.me>
References: <565f816b$0$3054$426a74cc@news.free.fr> <77dedcc2-f07c-4234-9b5c-22993b04c6d1@googlegroups.com> <565f9194$0$4565$426a74cc@news.free.fr> <31f29220-8f05-42a4-b62e-59eec378b924@googlegroups.com> <bu8akc-reu.ln1@s.simpson148.btinternet.com> <5fa6a8a6-389b-4ed0-ae37-941d5fd6d358@googlegroups.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Injection-Date: Mon, 21 Dec 2015 14:25:41 -0000 (UTC)
Injection-Info: mx02.eternal-september.org; posting-host="5c7a52e8d8bef31920cedcbb61c44150"; logging-data="7150"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1+rmUDFSyrwejIrwui58fng"
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:38.0) Gecko/20100101 Thunderbird/38.2.0
In-Reply-To: <5fa6a8a6-389b-4ed0-ae37-941d5fd6d358@googlegroups.com>
Cancel-Lock: sha1:Bg6nq2BoA7tegy57WZZIGLIDHOw=
Xref: csiph.com comp.lang.java.programmer:33379

On 12/17/15 3:36 PM, Lew wrote:
>
> You define a constant variable in B and refer to it from A.
>
> You recompile B with a different constant value.
>
> You then run A without recompiling it. Magically, it refers to the old value of the B constant.
>
> Because the constant was inlined in A, it stopped looking like a variable, so the runtime linkage doesn't refer to the constant from B, but uses the inlined value already in A.
> http://javasplitter.blogspot.com/2011/10/static-final-inline-trap.html

I've seen Java software use this to ensure that the components in use 
are consistent. E.g.,

class A {
  public static final int VERSION=3;
  public int getVersion() {
    return VERSION;
  }
}

class B {
  public static void main(String[] args) {
    if (A.getVersion()  // The version we're running with
     !=A.VERSION) {  // The version we were compiled with
      uhoh();
    }
  }
}

Mike Amling
--
QnV0IEkgZG9uJ3QgcmVjYWxsIHdoYXQgcHJvZ3JhbSBJIHNhdyB0aGlzIGluLg==