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Re: Casts and special things of the Java language

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Roedy Green <see_website@mindprod.com.invalid> writes:

> On Sat, 02 Apr 2011 22:04:03 +0200, Merciadri Luca
> <Luca.Merciadri@student.ulg.ac.be> wrote, quoted or indirectly quoted
> someone who said :
>
>>I'm wondering what will be displayed on the console.
>
> Seriously, what are you afraid will happen if you RUN the program?
>
> Why would you trust strangers on the Internet to tell you more than
> your own eyes?
>
> Surely you have managed to get a HelloWorld compiled and executing by
> now.  Your questions show you are well beyond the rank beginner stage.
>
> The compiler is well debugged.  Unless you are writing a compiler and
> need the equivalent of supreme court rulings on the meaning of the
> JLS, experiments on how Javac.exe/java.exe behaves won't mislead you.
> In any case, they are more accurate than off the hip answers you may
> get here.
>
> Further, the practical knowledge of how the compiler actually behaves
> is what you need to write programs, not how it should behave.

I know that when I run the bytecode, I get

==
1
1
0
1
1
0
==
(which shows my guesses are correct).

What I need to understand is WHY these values are displayed (and not
WHAT is displayed). That is, I need to understand the intrinsical
mechanism of this.

For example, numbering System.out.println console outputs from 1 to 6,
I can justify that

* output 2 is 1 (because of the return method);
* output 3 is 0 (because of the a.v = 0 instruction);
* output 4 is 1 (because of the b.v = 1 instruction).

However, I don't really understand outputs 1, 5 and 6. I would say:

* output 1 is 1 because b.m() is called thanks to the A a = b
  instruction (because a gets the methods of b, which is a B);
* output 5 is 1 because casting b (of type B) to an A does not change
  its (those of b) methods;
* output 6 is 0 because casting b (of type B) to an A leads to the
  following equality: ((A) b).v == a.v.

I would appreciate to know if I'm right (I might detail my
explanations if necessary), and, if not, I would like to learn what
really happens in these instructions. (Do not hesitate to give me
pointers.)

Thanks.

- -- 
Merciadri Luca
See http://www.student.montefiore.ulg.ac.be/~merciadri/
- -- 

Effort is important, but knowing where to make an effort makes all
  the difference!
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Casts and special things of the Java language Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-04-02 22:04 +0200
  Re: Casts and special things of the Java language Lew <noone@lewscanon.com> - 2011-04-02 17:22 -0400
  Re: Casts and special things of the Java language Roedy Green <see_website@mindprod.com.invalid> - 2011-04-02 21:31 -0700
    Re: Casts and special things of the Java language Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-04-03 11:16 +0200
      Re: Casts and special things of the Java language Merciadri Luca <merciadriluca@gmail.com> - 2011-04-03 09:01 -0700
        Re: Casts and special things of the Java language markspace <-@.> - 2011-04-03 10:53 -0700
          Re: Casts and special things of the Java language Merciadri Luca <merciadriluca@gmail.com> - 2011-04-03 11:28 -0700
            Re: Casts and special things of the Java language markspace <-@.> - 2011-04-03 13:35 -0700
              Re: Casts and special things of the Java language Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-04-03 22:58 +0200
            Re: Casts and special things of the Java language Lew <noone@lewscanon.com> - 2011-04-06 12:32 -0400

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