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Re: about class dependancies

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On Thursday, December 17, 2015 at 12:45:27 AM UTC-8, Steven Simpson wrote:
> On 17/12/15 02:27, Lew wrote:
> > On Wednesday, December 2, 2015 at 4:49:41 PM UTC-8, regis wrote:
> >> On 12/03/15 01:32, Lew wrote:
> >>> On Wednesday, December 2, 2015 at 3:40:46 PM UTC-8, regis wrote:
> >>>> let say we have some public class A
> >>>> that depends on some public class B, e.g.:
> >>>>
> >>>> ====
> >>>> // B.java
> >>>> public class B {
> >>>>      public int f(int n) { return 2*n; }
> >>>> }
> >>>> ====
> >>>> // A.java
> >>>> public class A {
> >>>>      public static void main (String[] args) {
> >>>>        B b= new B ();
> >>>>        System.out.println (b.f(5));
> >>>>      }
> >>>> }
> >>>> ====
> >>>> $ javac A.java B.java
> >>>> $ java A
> >>>> 10
> >>>> ====
> >>>>
> >>>> Then let say class B changes (with signature of f() unchanged), e.g.:
> >>>>
> >>>> ====
> >>>> // B.java, changed
> >>>> public class B {
> >>>>      int lambda= 10;
> >>>>      public int f(int n) { return lambda*n; }
> >>>> }
> >>>> ====
> >>>>
> >>>> Finally, we update file B.class, but not file A.class,
> >>>>
> >>>> ====
> >>>> $ javac B.java        # but not A.java
> >>>> $ java A
> >>>> 50
> >>>> ====
> >>>>
> >>>> It seems to work, but is it guaranteed ?
> >>>> or should file A.class still be updated ?
> >>
> >>> The Java compiler "javac" is smart enough to resolve many dependencies, including the one you note here.
> >>> However, this would not work if 'lambda' (*terrible* name for that variable!) were made 'final', and therefore a constant variable.
> >>
> >> It still seems to work if it is made final...
> >>
> >> // B.java, changed
> >> public class B {
> >>      final int multiplier= 1000;
> >>      public int f(int n) { return multiplier*n; }
> >> }
> >> ====
> >> $ javac B.java          # but not A.java
> >> $ java A
> >> 5000
> > That isn't what I meant. I meant if you recompile 'A' but not 'B" then you don't pick up the change in 'B'. What you did was recompile 'B' and run 'A'. I had misread your example.
> 
> I don't get it.  A.java refers to B, so compiling A.java will also 
> compile B.java as an implicit class, unless you have implicit 
> compilation turned off.

Yeah, my mistake. Let me try to get it right this time.

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 apologize for the confusion.

-- 
Lew

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Thread

about class dependancies regis <regis.barbanchon@free.fr> - 2015-12-03 00:40 +0100
  Re: about class dependancies Lew <lewbloch@gmail.com> - 2015-12-02 16:32 -0800
    Re: about class dependancies regis <regis.barbanchon@free.fr> - 2015-12-03 01:49 +0100
      Re: about class dependancies regis <regis.barbanchon@free.fr> - 2015-12-03 02:26 +0100
        Re: about class dependancies Arne Vajhøj <arne@vajhoej.dk> - 2015-12-02 21:55 -0500
          Re: about class dependancies Arne Vajhøj <arne@vajhoej.dk> - 2015-12-02 21:58 -0500
        Re: about class dependancies Steven Simpson <ss@my.domain.invalid> - 2015-12-03 15:15 +0000
          Re: about class dependancies Arne Vajhøj <arne@vajhoej.dk> - 2015-12-03 19:49 -0500
      Re: about class dependancies Lew <lewbloch@gmail.com> - 2015-12-16 18:27 -0800
        Re: about class dependancies Steven Simpson <ss@my.domain.invalid> - 2015-12-17 08:39 +0000
          Re: about class dependancies Lew <lewbloch@gmail.com> - 2015-12-17 13:36 -0800
            Re: about class dependancies Mike Amling <mamling@chaff.us> - 2015-12-21 08:29 -0600
  Re: about class dependancies regis <regis.barbanchon@free.fr> - 2015-12-03 02:07 +0100
    Re: about class dependancies Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-12-03 08:06 -0500

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