Clarification on Sefl test - K&B book

[Omer Haderi]

Hi there,

I have a question about the first question on self test page 158 K&B book.

It seems to me that none of the options is 100% correct, the book marks
B. (Has-a relationship always rely on instance variables.), but an object may have static references to other objects.

Is this an errata or I miss something ?

Thank you.

[Chandra Bhatt]

Ummmmmmmmm.....

but an object may have static references to other objects.

Game of words!!! "static references" Good!

Anybody comment please!


Regards,
cmbhatt

[Richard Boren]

And I was patting myself on the back for getting that one right.

Has-a relationship always rely on instance variables.

Should �variable� be left off?

static SomeObject obj = new SomeObject() ;

obj is a static variable. Yes?
obj is referencing a SomeObject instance. Yes?

Do I have this all wrong?

Richard

[Chandra Bhatt]

Good Richard,

Reference variables can be static, but objects are not!!!



Regards,
cmbhatt

[swarna dasa]

Actually i too got it wrong and convinced myself that "HAS-A" makes sense only with instance variables. Though i am not completely convinced

Lets try this example (though not a perfect one)

Lets say Honda always have a particular kind of audio system (Bose) and this will never change (Remember its not a perfect example).


class Honda {
final static BoseSpeakerSystem speaker = new BoseSpeakerSystem();
//can override other functions
...
...
...
}

class BoseSpeakerSystem extends SpeakerSystem{
}

In this case can we say all Honda cars have a Bose Speaker System?

[Omer Haderi]

Hello again,

I couldn't find any good explanation for this, so I will try to get it right through another question... :roll:

if the following is considered to have a "Has-a" relationship then the answer b of the book is an errata.

    
class A {} 
 
class B {
  private static A obj;
}

otherwise I miss something from that question.

[Richard Boren]

Hi Omer,

The book says �Is-a� is based on class inheritance or interface (p. 90; 1st para under IS-A)

I don�t see enxtends or implenents in your example. So I�d say it is a �Has-a�. And obviously obj is not an "instance variable". It looks like answer (b) is not 100% correct as you have stated.

otherwise I miss something from that question.

Me too. Sorry no answer, same question.

Richard

[swarna dasa]

Still on the look out for a convincing answer... :roll:

[Burkhard Hassel]

Hi ranchers,

perhaps read what Javier wrote here (some time ago):
http://www.coderanch.com/t/258840/java-programmer-SCJP/certification/Has-relationship


The errata could be found here:
http://www.coderanch.com/t/257589/java-programmer-SCJP/certification/SCJP-Errata-Updated


And, by the way, nothing can be an errata...


Yours,
Bu.

[Srinivasan thoyyeti]

Hi Ranchers,

I feel there is difference guys.

Class Has-A staticObject.

ClassObject Has-A instanceObject.

When you say ClassObject has an Object, it must be in its ClassObjectState.

ClassObject can use/share the static context Objects. its common behavior for all ClassObjects to share static context.

[Pankaj Patel]

Are STATIC Object OR Reference IS a part of Object.
NO.
IT IS A PART OF CLASS.
SO IT(has-a Relation) IS TOTALLY DEPENDENT ON INSTANCE VARIABLE.


AM I RIGHT?
[ April 19, 2007: Message edited by: Pankaj Patel ]