some one please explain this

Question

3.50/5 (2 votes)

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Hi Friends,

Can anyone give me a explnation for this program??

in Java the output :

Hi From derived

in C# the Output :

Hi From base

Why oops concept diffrent in both langauges ?

but in both language - the object type is derived class

C#

class Program
 {
     static void Main(string[] args)
     {
         MyClass A= new MyClass1();
         A.h1();

         System.Type type = A.GetType();
         Console.WriteLine(type.ToString());
         
     }
 }
 public class MyClass
 {
     
     public void h1()
     {
         Console.WriteLine("Hi From base");
     }

 }
public class MyClass1 :MyClass
 {
     public void h1()
     {
         Console.WriteLine("Hi From derived");
     }
     
 }

Posted 30-Mar-12 7:01am

froxy

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Comments

Shahin Khorshidnia 30-Mar-12 15:41pm

Good Question!

Sergey Alexandrovich Kryukov 30-Mar-12 22:01pm

I think this is no more but an elementary bug. And if the question was good, it would contain sample code in two languages, not just one. Nevertheless, it's easy to see what's the problem.
--SA

Shahin Khorshidnia 31-Mar-12 6:11am

Of course, but it's a very common question (Although simple) I've seen many beginners (in C#) that are making the mistake.

2 solutions

Solution 2

Fix the warnings first! Each warning might be a problem.
And you run now into a hiding issue.
I guess you had a warning while you did compile C#, right?

IIRC, in Java, all is virtual, while in C# only the so declared methods are.
(I'm not a Java programmer, though)

[EDIT]
This is the warning you get for C# in Visual Studio 2010:

Warning 1 'ConsoleApplication1.MyClass1.h1()' hides inherited member 'ConsoleApplication1.MyClass.h1()'. Use the new keyword if hiding was intended.

But I have to admit: when pressing F1 in Visual Studio 2010 on that warning to get more details on it, the help text from Microsoft is crap. No word about virtual/override. The simplest solution is not given: rename the hiding member, nor any word about virtual/overriding is given...
I would say: "no one" ever wants to hide a memeber - calls for maintenance trouble.
Any example why one would want to hide a member by applying the new keyword?
[/EDIT]

Posted 30-Mar-12 8:44am

Andreas Gieriet

Updated 1-Apr-12 4:13am

v2

Comments

Sergey Alexandrovich Kryukov 30-Mar-12 21:59pm

But that a good point (about warnings), my 5.
--SA

Andreas Gieriet 31-Mar-12 2:02am

Thanks for your 5! Why the other vote is a 2 would be interesting though... in this case, the warning would have told the problem, assuming one knows what hiding means...

Sergey Alexandrovich Kryukov 1-Apr-12 0:15am

Always a please to mark a good answers. As to the 2... I noticed that somebody often down-vote, for example, any strong opinion, or sometimes, any answer not presenting a ready-to-use cookbook code sample.

Now, about this warning, we has some misunderstanding when I considered the OP's code sample as a bug. (Please see other comments.) I believe, originally, that was mostly the lack of knowledge of the syntax, but paying attention for the warning could help to resolve the problem by learning it, quite easily. That's how such warning could be critically important.

--SA

Andreas Gieriet 1-Apr-12 1:39am

I initially got your statement on the bug wrong - with your explanation it is now clear that you meant the OP's code to have a bug.
Cheers
Andi

Sergey Alexandrovich Kryukov 1-Apr-12 14:23pm

As two other experts got it wrong, I guess I did not express myself clearly. Hopefully, we now understand each other.
Thank you,
--SA

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Not Active · Accepted Answer · 2012-03-30T07:09:00

Solution 1

If you want the method to be overridden in a derived class you need to mark it as virtual in the base.

C#

public class MyClass
 {

     public virtual void h1()
     {
         Console.WriteLine("Hi From base");
     }

 }
public class MyClass1 :MyClass
 {
     public override void h1()
     {
         Console.WriteLine("Hi From derived");
     }

 }

As you have it your instance of MyClass, A, only knows of the h1 method it contains.

Posted 30-Mar-12 7:09am

Not Active

Updated 30-Mar-12 7:12am

v3

Comments

Shahin Khorshidnia 30-Mar-12 15:38pm

My +5

Sergey Alexandrovich Kryukov 30-Mar-12 21:59pm

Exactly, a 5.
That said, OOP concepts are not really different in those language in this respect; this can be considered as a bug in C#, that's it.
--SA

Andreas Gieriet 31-Mar-12 1:59am

I might disagree: I don't see this as a bug. C# provides more fine grained control over the method declaration compared to Java. If it was a wise decision to have non-virtual as default in C# is another question. May be, it has to be viewed as a legacy.

Sergey Alexandrovich Kryukov 1-Apr-12 0:09am

Perhaps you misunderstood what I meant as a bug (because I did not express myself clearly). The bug is OP's code: it looks like OP assumed overridden function without abstract/virtual/override syntax, and also ignored the warning. That is a bug.

--SA

[no name] 31-Mar-12 13:32pm

Since this functionality is present in C++ and, I believe Delphi, which is the basis for C# I would say it is a well-thought design decision not a bug.

Sergey Alexandrovich Kryukov 1-Apr-12 0:08am

Yes, Delphi mechanism is the closest to C#. Delphi is its most direct predecessor (not Java).

Perhaps you misunderstood what I meant as a bug (and I did not express myself clearly). The bug is OP's code: it looks like OP assumed overridden function without abstract/virtual/override syntax, and also ignored the warning. That is a bug.

As to what you call a well-thought decision. If you mean .NET/C# syntax and default semantic (which is exactly the same is in Delphi), I think you are absolutely right. Such design is optimal, in my opinion.

--SA