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  Class ... implements ... Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-04-02 22:13 +0200
    Re: Class ... implements ... Lew <noone@lewscanon.com> - 2011-04-02 17:30 -0400
      Re: Class ... implements ... Roedy Green <see_website@mindprod.com.invalid> - 2011-04-02 23:09 -0700
      Re: Class ... implements ... Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-04-03 12:00 +0200
    Re: Class ... implements ... Roedy Green <see_website@mindprod.com.invalid> - 2011-04-02 20:53 -0700
      Re: Class ... implements ... Stanimir Stamenkov <s7an10@netscape.net> - 2011-04-03 10:15 +0300
    Re: Class ... implements ... Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-04-03 08:42 -0400
      Re: Class ... implements ... Roedy Green <see_website@mindprod.com.invalid> - 2011-04-03 06:45 -0700
        Re: Class ... implements ... Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-04-03 17:29 +0200
          Re: Class ... implements ... Patricia Shanahan <pats@acm.org> - 2011-04-03 09:01 -0700
            Re: Class ... implements ... Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-04-03 18:10 +0200
              Re: Class ... implements ... Patricia Shanahan <pats@acm.org> - 2011-04-03 09:32 -0700
                Re: Class ... implements ... Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-04-03 18:48 +0200
          Re: Class ... implements ... Aéris <aeris@imirhil.fr> - 2011-04-03 18:07 +0200
            Re: Class ... implements ... Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-04-03 18:22 +0200
              Re: Class ... implements ... Aéris <aeris@imirhil.fr> - 2011-04-03 19:02 +0200
                Re: Class ... implements ... Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-04-03 20:15 +0200
        Re: Class ... implements ... Lew <noone@lewscanon.com> - 2011-04-06 12:01 -0400
      Re: Class ... implements ... Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-04-03 17:27 +0200
        Re: Class ... implements ... Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-04-03 14:26 -0400
        Re: Class ... implements ... Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-04-03 16:14 -0300
          Re: Class ... implements ... Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-04-03 21:33 +0200
            Re: Class ... implements ... Aéris <aeris@imirhil.fr> - 2011-04-03 22:13 +0200
              Re: Class ... implements ... Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-04-03 22:24 +0200
        Re: Class ... implements ... Lew <noone@lewscanon.com> - 2011-04-06 12:05 -0400
      Re: Class ... implements ... Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-04-03 17:31 +0200
        Re: Class ... implements ... Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-04-03 14:41 -0400
          Re: Class ... implements ... Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-04-03 21:45 +0200
            Re: Class ... implements ... Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-04-03 16:40 -0400
              Re: Class ... implements ... Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-04-03 22:58 +0200
                Re: Class ... implements ... Lew <noone@lewscanon.com> - 2011-04-06 12:13 -0400
            Re: Class ... implements ... Lew <noone@lewscanon.com> - 2011-04-06 12:10 -0400
          Re: Class ... implements ... Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-04-03 21:51 +0200
            Re: Class ... implements ... Patricia Shanahan <pats@acm.org> - 2011-04-03 13:02 -0700
              Re: Class ... implements ... Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-04-03 22:23 +0200
            Re: Class ... implements ... Lew <noone@lewscanon.com> - 2011-04-06 12:15 -0400
        Re: Class ... implements ... Lew <noone@lewscanon.com> - 2011-04-06 12:08 -0400

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#520

On 11-04-03 12:27 PM, Merciadri Luca wrote:
[ SNIP ]

> Thanks for the tips. I'll try to get a textbook. The problem is that
> I'm learning Java for some course and that I don't have a sufficient
> amount of (academic) time to learn Java in depth. So I'll try to do my best.

Ideally you're not learning Java only to pass a course, although it's
good if you do pass the course. :-) Having said that, what kind of
course is it where you have to learn Java but don't even have a textbook
for it?

At this starter level you honestly don't even need a textbook - you
really don't. What you need to know - minimum - can be found at
http://download.oracle.com/javase/tutorial/, specifically in the "Trails
Covering The Basics" section. If you read and understand this you'll
save yourself a lot of time and effort. No textbook out there is going
to do a better job at explaining the basics. The very first Java printed
reference I ever had (and still have) was 2nd edition "Java In A
Nutshell", 1997, covering Java 1.1, and looking at it now I see that
there's nothing in it that wouldn't be available online. I doubt the
later editions are qualitatively different.

You've already invested a fair bit of effort in this by asking questions
here, and a somewhat painful process it's been. If you look at the Java
Tutorials now, I suspect a fair few things will fall into place.

If you don't mind me asking, is this also your first programming language?

AHS
-- 
That's not the recollection that I recall...All this information is
certainly in the hands of the auditor and we certainly await his report
to indicate what he deems has occurred.
-- Halifax, Nova Scotia mayor Peter Kelly, who is currently deeply in
the shit

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#521

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Arved Sandstrom <asandstrom3minus1@eastlink.ca> writes:

> On 11-04-03 12:27 PM, Merciadri Luca wrote:
> [ SNIP ]
>
>> Thanks for the tips. I'll try to get a textbook. The problem is that
>> I'm learning Java for some course and that I don't have a sufficient
>> amount of (academic) time to learn Java in depth. So I'll try to do my best.
>
> Ideally you're not learning Java only to pass a course, although it's
> good if you do pass the course. :-) Having said that, what kind of
> course is it where you have to learn Java but don't even have a textbook
> for it?
>
> At this starter level you honestly don't even need a textbook - you
> really don't. What you need to know - minimum - can be found at
> http://download.oracle.com/javase/tutorial/, specifically in the "Trails
> Covering The Basics" section. If you read and understand this you'll
> save yourself a lot of time and effort. No textbook out there is going
> to do a better job at explaining the basics. The very first Java printed
> reference I ever had (and still have) was 2nd edition "Java In A
> Nutshell", 1997, covering Java 1.1, and looking at it now I see that
> there's nothing in it that wouldn't be available online. I doubt the
> later editions are qualitatively different.
>
> You've already invested a fair bit of effort in this by asking questions
> here, and a somewhat painful process it's been. If you look at the Java
> Tutorials now, I suspect a fair few things will fall into place.
>
> If you don't mind me asking, is this also your first programming language?

I'll look at your link. Not at all my first programming language, but
sure I'm not really confident with some aspects of OOP, especially
here because of the differences between experts and a beginner like
me. Well, some concepts are installing progressively.

There is no problem about the course, which is well taught. The
problem is that some questions are asked on specific aspects of
the Java language (such as some aspects over which I asked questions
earlier), and a normal student could not be answer all these questions
by only reading the slides, which already provide important
information.

As a result, I'll need to document myself for some specific
aspects. I'm conscient of this.
- -- 
Merciadri Luca
See http://www.student.montefiore.ulg.ac.be/~merciadri/
- -- 

If it's worth doing, it's worth over-doing.
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#525

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Le 03/04/2011 21:33, Merciadri Luca a écrit :
> The
> problem is that some questions are asked on specific aspects of
> the Java language

No, most of your questions is only in the OOP scope, not in the Java one.
Your questions can be applied on C# or Python instead of Java without
changing the responses, for example about inheritance, up/down-casting,
equals/identity, accessor scope and accessibility, etc.

- -- 
Aeris
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#527

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Aéris <aeris@imirhil.fr> writes:

> Le 03/04/2011 21:33, Merciadri Luca a écrit :
>> The
>> problem is that some questions are asked on specific aspects of
>> the Java language
>
> No, most of your questions is only in the OOP scope, not in the Java one.
> Your questions can be applied on C# or Python instead of Java without
> changing the responses, for example about inheritance, up/down-casting,
> equals/identity, accessor scope and accessibility, etc.

Okay, then. I learnt something new again. Well, I think that I'll read
a lot these days about Java mechanisms, so that I will be able to give
more interesting, precise and detailed questions.

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

In the land of the blind, the one-eyed man is king.
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#548

Merciadri Luca wrote:
> Thanks for the tips. I'll try to get a textbook. The problem is that
> I'm learning Java for some course and that I don't have a sufficient
> amount of (academic) time to learn Java in depth. So I'll try to do my best.

Once again, Merciadri,
<http://download.oracle.com/javase/tutorial/index.html>

It's free.

Did you miss this recommendation earlier?

-- 
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg

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#502

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Eric Sosman <esosman@ieee-dot-org.invalid> writes:

> On 4/2/2011 4:13 PM, Merciadri Luca wrote:
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>> Hi,
>>
>> I'm given the following program snippet:
>>
>> ==
>> class C1
>> {
>>   public int n;
>> }
>>
>> interface I1
>> {
>>   int f();
>> }
>>
>> class C2 extends C1 implements I1
>> {
>>   public int f()
>>   {
>>    n = 18;
>>   }
>> }
>> ==
>> I need to say if the following expressions are valid or not
>> (justifications are trivial once I'm sure of the answer):
>>
>> 1. C1 obj_1 = new C2();
>
>     Invalid.
>
>> 2. C2 obj_2 = new C1();
>
>     Invalid.
>
>> 3. I1 obj_3 = new C2();
>
>     Invalid.
>
>> 4. I1 obj_4 = new I1();
>
>     Invalid.
>
>> 5. C2 obj_5 = new I1();
>
>     Invalid.
> I predict you will get compile-time
> errors for all five of them.

Okay, I just tested and received the results I wrote before.

==
$ javac Test.java
Test.java:25: incompatible types
found   : C1
required: C2
C2 obj_2 = new C1();
           ^
Test.java:27: I1 is abstract; cannot be instantiated
I1 obj_4 = new I1();
           ^
Test.java:28: I1 is abstract; cannot be instantiated
C2 obj_5 = new I1(); 
           ^
3 errors
==
so that the three operations I mentioned as invalid are effectively
(at least to my little knowledge) invalid.

Do you have an explanation about your way of reasoning? My compiler
might be too old, or something like that.

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

If you want to judge a man's character, give him power.
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#519

On 4/3/2011 11:31 AM, Merciadri Luca wrote:
> Eric Sosman<esosman@ieee-dot-org.invalid>  writes:
>> [...]
>> I predict you will get compile-time
>> errors for all five of them.
>
> Okay, I just tested and received the results I wrote before.
>[...]
> Do you have an explanation about your way of reasoning? My compiler
> might be too old, or something like that.

     I think it less likely that your compiler is broken than that
you put the wrong code through it.  Allow me to draw your attention
to method f() of class C2: What value does it return?  (In the
version you posted, not the version you've been compiling.)

-- 
Eric Sosman
esosman@ieee-dot-org.invalid

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#522

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Eric Sosman <esosman@ieee-dot-org.invalid> writes:

> On 4/3/2011 11:31 AM, Merciadri Luca wrote:
>> Eric Sosman<esosman@ieee-dot-org.invalid>  writes:
>>> [...]
>>> I predict you will get compile-time
>>> errors for all five of them.
>>
>> Okay, I just tested and received the results I wrote before.
>>[...]
>> Do you have an explanation about your way of reasoning? My compiler
>> might be too old, or something like that.
>
>     I think it less likely that your compiler is broken than that
> you put the wrong code through it.  Allow me to draw your attention
> to method f() of class C2: What value does it return?  (In the
> version you posted, not the version you've been compiling.)

It returns nothing, but as it is declared as an int method, it needs
to return an int. Well, I added return n. What I sent over the valid
and non valid instructions is effectively what I got by compiling the
same code, but with a return where it was missing. 

I now understand your
answer. I can't understand why people are sometimes so `picky' in some
answers. This often go anti-pedagogical.

That reminds me an oral exam. I had to prove some theorem on the board, wrote
something like 98% of the proof, but forgot some things. Well, the
proof was not complete, and the theorem was thus unproved, but is it a
reason to say `totally erroneous?' Sure not, at least to me. It is
better to say `well, you forgot some things.' Especially when the
related mark is however high. This got many students completely
frustrated, shocked, and unable to answer anymore at an oral. This is
not what needs to be evaluated at an oral exam!

Here, if I may, you answered correctly the question, but note that it
brought me nothing interesting, simply because I did not understand
your message, even if it was perfectly correct and irreproachable.

Wouldn't it have been simpler, more pedagogic, and even `friendler,'
to say `this way, there will be a problem with some method. Check it,
because this is surely not the aim of this exercise.'

You already knew that the aim of the exercise was to check student's
knowledge about a totally different concept than a basic thing such as
the fact that an int function needs to return an int, just as it would
in C.

And this is often an attitude I do not appreciate, since it brings
nothing to the student, except some frustration. Going pedagogic is so
much better, especially when it comes to help a student.

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

Remember. If something can go wrong, it will. 
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#529

On 4/3/2011 3:45 PM, Merciadri Luca wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Eric Sosman<esosman@ieee-dot-org.invalid>  writes:
>
>> On 4/3/2011 11:31 AM, Merciadri Luca wrote:
>>> Eric Sosman<esosman@ieee-dot-org.invalid>   writes:
>>>> [...]
>>>> I predict you will get compile-time
>>>> errors for all five of them.
>>>
>>> Okay, I just tested and received the results I wrote before.
>>> [...]
>>> Do you have an explanation about your way of reasoning? My compiler
>>> might be too old, or something like that.
>>
>>      I think it less likely that your compiler is broken than that
>> you put the wrong code through it.  Allow me to draw your attention
>> to method f() of class C2: What value does it return?  (In the
>> version you posted, not the version you've been compiling.)
>
> It returns nothing, but as it is declared as an int method, it needs
> to return an int. Well, I added return n. What I sent over the valid
> and non valid instructions is effectively what I got by compiling the
> same code, but with a return where it was missing.
>
> I now understand your
> answer. I can't understand why people are sometimes so `picky' in some
> answers. This often go anti-pedagogical.

     If you pose a question that requires the answerer to imagine
some kind of repair or completion, different answerers are likely to
imagine different completions and may therefore give different
answers.  One reader fleshes out your code *this* way and says "Yes,"
another completes it *that* way and says "No."  Who's right?  Both!
What have you learned, having been told both "Yes" and "No?"  Nothing!

     If you dislike pickiness, get out of programming.  Seriously.  The
computer is far, far pickier than any human can be.

> That reminds me an oral exam. I had to prove some theorem on the board, wrote
> something like 98% of the proof, but forgot some things. Well, the
> proof was not complete, and the theorem was thus unproved, but is it a
> reason to say `totally erroneous?' Sure not, at least to me. It is
> better to say `well, you forgot some things.' Especially when the
> related mark is however high. This got many students completely
> frustrated, shocked, and unable to answer anymore at an oral. This is
> not what needs to be evaluated at an oral exam!

     Writing on a blackboard and waving your hands and operating the
smoke-and-mirrors machine for a human audience is one thing; writing
code and giving it to a completely unimaginative compiler is another.
If you think you can write 98% of a program and have it work, you are
in the wrong line of work altogether.

     (Also, I did not use the phrase "totally erroneous."  I called
your code "a half-remembered half-accurate half-assed approximation."
I'm not sure "totally erroneous" is even possible, since there does
not seem to be an upper bound on error: Any program, however bad, can
always be disimproved -- or so I suspect.)

> Here, if I may, you answered correctly the question, but note that it
> brought me nothing interesting, simply because I did not understand
> your message, even if it was perfectly correct and irreproachable.

     That's because you're lazy.  Or inattentive.  Or both.

> Wouldn't it have been simpler, more pedagogic, and even `friendler,'
> to say `this way, there will be a problem with some method. Check it,
> because this is surely not the aim of this exercise.'

     Have you heard about giving a man a fish versus teaching him to
fish?  Here's the point: You have questions about Code Sample A, and
you show us Code Sample B instead.  Therefore you get wrong answers.
My pedagogic purpose was to teach you the folly of pretending A == B.
I claim that my purpose has been achieved: You have been taught the
lesson, even though you clearly resent learning it.

     Besides, you have already told us that you do not wish to learn
Java "in depth," so why complain about shallow answers?  It's odd for
an admitted non-learner to harp on pedagogy.

-- 
Eric Sosman
esosman@ieee-dot-org.invalid

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#530

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Eric Sosman <esosman@ieee-dot-org.invalid> writes:

> On 4/3/2011 3:45 PM, Merciadri Luca wrote:
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>> Eric Sosman<esosman@ieee-dot-org.invalid>  writes:
>>
>>> On 4/3/2011 11:31 AM, Merciadri Luca wrote:
>>>> Eric Sosman<esosman@ieee-dot-org.invalid>   writes:
>>>>> [...]
>>>>> I predict you will get compile-time
>>>>> errors for all five of them.
>>>>
>>>> Okay, I just tested and received the results I wrote before.
>>>> [...]
>>>> Do you have an explanation about your way of reasoning? My compiler
>>>> might be too old, or something like that.
>>>
>>>      I think it less likely that your compiler is broken than that
>>> you put the wrong code through it.  Allow me to draw your attention
>>> to method f() of class C2: What value does it return?  (In the
>>> version you posted, not the version you've been compiling.)
>>
>> It returns nothing, but as it is declared as an int method, it needs
>> to return an int. Well, I added return n. What I sent over the valid
>> and non valid instructions is effectively what I got by compiling the
>> same code, but with a return where it was missing.
>>
>> I now understand your
>> answer. I can't understand why people are sometimes so `picky' in some
>> answers. This often go anti-pedagogical.
>
>     If you pose a question that requires the answerer to imagine
> some kind of repair or completion, different answerers are likely to
> imagine different completions and may therefore give different
> answers.  One reader fleshes out your code *this* way and says "Yes,"
> another completes it *that* way and says "No."  Who's right?  Both!
> What have you learned, having been told both "Yes" and "No?"  Nothing!
>
>     If you dislike pickiness, get out of programming.  Seriously.  The
> computer is far, far pickier than any human can be.
>
>> That reminds me an oral exam. I had to prove some theorem on the board, wrote
>> something like 98% of the proof, but forgot some things. Well, the
>> proof was not complete, and the theorem was thus unproved, but is it a
>> reason to say `totally erroneous?' Sure not, at least to me. It is
>> better to say `well, you forgot some things.' Especially when the
>> related mark is however high. This got many students completely
>> frustrated, shocked, and unable to answer anymore at an oral. This is
>> not what needs to be evaluated at an oral exam!
>
>     Writing on a blackboard and waving your hands and operating the
> smoke-and-mirrors machine for a human audience is one thing; writing
> code and giving it to a completely unimaginative compiler is another.
> If you think you can write 98% of a program and have it work, you are
> in the wrong line of work altogether.
>
>     (Also, I did not use the phrase "totally erroneous."  I called
> your code "a half-remembered half-accurate half-assed approximation."
> I'm not sure "totally erroneous" is even possible, since there does
> not seem to be an upper bound on error: Any program, however bad, can
> always be disimproved -- or so I suspect.)
>
>> Here, if I may, you answered correctly the question, but note that it
>> brought me nothing interesting, simply because I did not understand
>> your message, even if it was perfectly correct and irreproachable.
>
>     That's because you're lazy.  Or inattentive.  Or both.
>
>> Wouldn't it have been simpler, more pedagogic, and even `friendler,'
>> to say `this way, there will be a problem with some method. Check it,
>> because this is surely not the aim of this exercise.'
>
>     Have you heard about giving a man a fish versus teaching him to
> fish?  Here's the point: You have questions about Code Sample A, and
> you show us Code Sample B instead.  Therefore you get wrong answers.
> My pedagogic purpose was to teach you the folly of pretending A == B.
> I claim that my purpose has been achieved: You have been taught the
> lesson, even though you clearly resent learning it.
>
>     Besides, you have already told us that you do not wish to learn
> Java "in depth," so why complain about shallow answers?  It's odd for
> an admitted non-learner to harp on pedagogy.

Everybody wants to learn everything in depth. The fact is that there
are far more important things in my studies now. As a result, I want
to learn the basic and most important things in Java. I wrote a
project for the course, but it did not give me sufficient knowledge
about Java. Well, I can do many things, but I haven't yet the habit,
and it will take some time. Programming is clearly something that is
honed by years of practice.

All the best,

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

It's the early bird that gets the worm.
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#551

Merciadri Luca wrote:
> Everybody wants to learn everything in depth. The fact is that there

And some people are actually willing to study to do that.

> are far more important things in my studies now. As a result, I want

Well, then, there are far more important things for us to do than enable an 
ungrateful person who asks for advice then argues about it.

How arrogant can you be?  You even make me look humble.

> to learn the basic and most important things in Java. I wrote a

That's a flat-out lie.

You obviously want no such thing.  Otherwise you'd actually take the advice 
for which you ask,and you wouldn't be so proudly, arrogantly lazy about it.

> project for the course, but it did not give me sufficient knowledge
> about Java. Well, I can do many things, but I haven't yet the habit,
> and it will take some time. Programming is clearly something that is
> honed by years of practice.

And yet you won't spend minutes on it.  You're wasting everyone's time, most 
especially your own.  Is that really wise?

-- 
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg

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#550

Merciadri Luca wrote:
>I can't understand why people are sometimes so `picky' in some
> answers. This often go anti-pedagogical.

Because you ignore advice previously given, you don't do your own research, 
you don't seem to do any work on your own, and you get mad at the answers.

It's really not complicated.

-- 
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg

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#523

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And `going pedagogic' does not mean `doing others' homeworks.' That
just means pointing what is the most probable source of mistakes.

But I understood the error, and also my mistake. Now, we might agree
on the valid and invalid instructions.

Precision is important in programming, mathematics, and, more
generally, in every science, but nothing is more important
than a constructive discussion, or relationship.

All the best,

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

If you don't buy a ticket, you can't win the raffle.
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#524

On 4/3/2011 12:51 PM, Merciadri Luca wrote:
...
> Precision is important in programming, mathematics, and, more
> generally, in every science, but nothing is more important
> than a constructive discussion, or relationship.

When the subject of the discussion is programming or mathematics, often
precision is necessary for a constructive discussion. The less familiar
someone is with a programming language, the greater the risk that
something really important, that affects answers to their questions,
seems like an irrelevant detail to them.

Patricia

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#526

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Patricia Shanahan <pats@acm.org> writes:

> On 4/3/2011 12:51 PM, Merciadri Luca wrote:
> ...
>> Precision is important in programming, mathematics, and, more
>> generally, in every science, but nothing is more important
>> than a constructive discussion, or relationship.
>
> When the subject of the discussion is programming or mathematics, often
> precision is necessary for a constructive discussion. The less familiar
> someone is with a programming language, the greater the risk that
> something really important, that affects answers to their questions,
> seems like an irrelevant detail to them.

Sure, but that does not mean, to me, that the way he answered was the
right way to make me understand what was the error. But that is only a
point of view. It is possible to answer precisely and pedagogically.

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

If you want to judge a man's character, give him power.
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#552

Merciadri Luca wrote:
> Precision is important in programming, mathematics, and, more
> generally, in every science, but nothing is more important
> than a constructive discussion, or relationship.

Yet you do nothing to build one.

That's hypocritical.

-- 
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg

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#549

On 04/03/2011 11:31 AM, Merciadri Luca wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Eric Sosman<esosman@ieee-dot-org.invalid>  writes:
>
>> On 4/2/2011 4:13 PM, Merciadri Luca wrote:
>>> -----BEGIN PGP SIGNED MESSAGE-----
>>> Hash: SHA1
>>>
>>> Hi,
>>>
>>> I'm given the following program snippet:
>>>
>>> ==
>>> class C1
>>> {
>>>    public int n;
>>> }
>>>
>>> interface I1
>>> {
>>>    int f();
>>> }
>>>
>>> class C2 extends C1 implements I1
>>> {
>>>    public int f()
>>>    {
>>>     n = 18;
>>>    }
>>> }
>>> ==
>>> I need to say if the following expressions are valid or not
>>> (justifications are trivial once I'm sure of the answer):
>>>
>>> 1. C1 obj_1 = new C2();
>>
>>      Invalid.
>>
>>> 2. C2 obj_2 = new C1();
>>
>>      Invalid.
>>
>>> 3. I1 obj_3 = new C2();
>>
>>      Invalid.
>>
>>> 4. I1 obj_4 = new I1();
>>
>>      Invalid.
>>
>>> 5. C2 obj_5 = new I1();
>>
>>      Invalid.
>> I predict you will get compile-time
>> errors for all five of them.
>
> Okay, I just tested and received the results I wrote before.
>
> ==
> $ javac Test.java
> Test.java:25: incompatible types
> found   : C1
> required: C2
> C2 obj_2 = new C1();
>             ^
> Test.java:27: I1 is abstract; cannot be instantiated
> I1 obj_4 = new I1();
>             ^
> Test.java:28: I1 is abstract; cannot be instantiated
> C2 obj_5 = new I1();
>             ^
> 3 errors
> ==
> so that the three operations I mentioned as invalid are effectively
> (at least to my little knowledge) invalid.
>
> Do you have an explanation about your way of reasoning? My compiler
> might be too old, or something like that.

This question was answered in your first answer:
> Which expressions put a subtype instance into a supertype variable?
>
> Which expressions put a supertype instance into a subtype variable?
>
> How can a subtype variable be sure that a supertype instance is of the correct type?
>
> Are you allowed in Java to instantiate an interface?
>
> Please answer as best you can.  You should use the Java tutorials to help you; don't just randomly guess.  We will be expecting your responses.

Did you even engage with those hints?  If not, why expect more?

-- 
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg

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