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"IS-A" and "HAS-A" doubt

Kedar Pethe
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Joined: Jul 17, 2012
Posts: 39
K&B question in self test-

Q - You’re designing a new online board game in which Floozels are a type of Jammers, Jammers can
have Quizels, Quizels are a type of Klakker, and Floozels can have several Floozets. Which of the
following fragments represent this design?


Why isn't Fragment 4 one of the correct answers??
Pritish Chakraborty
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Joined: Jun 12, 2012
Posts: 91

Because Floozel does not HAVE-A Floozet.

Here it IS-A Floozet.


OCJP 6
Kedar Pethe
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Joined: Jul 17, 2012
Posts: 39
Pritish Chakraborty wrote:Because Floozel does not HAVE-A Floozet.

Here it IS-A Floozet.


oh.. So simple!!
Joe Harry
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Joined: Sep 26, 2006
Posts: 9427
    
    2

Pritish Chakraborty wrote:Because Floozel does not HAVE-A Floozet.

Here it IS-A Floozet.


Floozel HAS-A Floozet as per the question. The point here to take away is the following:

(1) IS-A relationship represents Inheritence
(2) HAS-A relationship represents Composition

Hope that was clear.


SCJP 1.4, SCWCD 1.4 - Hints for you, Certified Scrum Master
Did a rm -R / to find out that I lost my entire Linux installation!
Pritish Chakraborty
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Joined: Jun 12, 2012
Posts: 91

I'm sorry, I didn't get you....

Of course those two points are very clear but here Floozel and Floozet are two interfaces linked through inheritance, not through composition.

How does the HAS-A relationship come into question at all?
Joe Harry
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Joined: Sep 26, 2006
Posts: 9427
    
    2

Pritish Chakraborty wrote:I'm sorry, I didn't get you....

Of course those two points are very clear but here Floozel and Floozet are two interfaces linked through inheritance, not through composition.

How does the HAS-A relationship come into question at all?


Doesn't this sentence say that?



I would infer the following:

Quizels extends Klakker (are a type of Klakker) and when Floozels can have several Floozets, would mean Floozels has one to many Floozets as its member. How could I apply IS-A relationship here? Do you understand it now?

By the way, Answer option 4 is wrong. Any wrong answer in the SCJP exam is just to confuse you. The interface in the option 4 above is also to confuse you.
Pritish Chakraborty
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Joined: Jun 12, 2012
Posts: 91

My dear sir, with all due respect, I did read the question. I don't know if you did however.

The original poster was asking why the fourth fragment was wrong.

And it is wrong because the HAS-A relationship of Floozel and Floozet is NOT maintained, which is required as per the question.

It does not hurt to reread the query

Yes, we know option 4 is wrong. He was asking why it is wrong.

Good day to you, sir.
Joe Harry
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Joined: Sep 26, 2006
Posts: 9427
    
    2

Pritish Chakraborty wrote:My dear sir, with all due respect, I did read the question. I don't know if you did however.

The original poster was asking why the fourth fragment was wrong.

And it is wrong because the HAS-A relationship of Floozel and Floozet is NOT maintained, which is required as per the question.

It does not hurt to reread the query

Yes, we know option 4 is wrong. He was asking why it is wrong.

Good day to you, sir.


I don't get you. If you understood the question, then why ask the following in your post above?




Pritish Chakraborty
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Joined: Jun 12, 2012
Posts: 91

Let me clarify this confusion once and for all.

My reply to the OP's query was with respect to the code fragment he posted. He asked why it is wrong.

I answered why it is wrong.

The quote of my post which you have put in </code> tags was asked to you : because you were stating the obvious, and not answering the OP's query.

You were informing me what IS-A and HAS-A relationships are about, whereas the thread had gone in a completely different direction and had already been resolved.
Joe Harry
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Joined: Sep 26, 2006
Posts: 9427
    
    2

Pritish Chakraborty wrote:Let me clarify this confusion once and for all.

My reply to the OP's query was with respect to the code fragment he posted. He asked why it is wrong.

I answered why it is wrong.

The quote of my post which you have put in </code> tags was asked to you : because you were stating the obvious, and not answering the OP's query.

You were informing me what IS-A and HAS-A relationships are about, whereas the thread had gone in a completely different direction and had already been resolved.


The idea here is to mention about composition and Inheritence which I felt I did!
 
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