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what is the need to declare a class abstract if it doesn't contain abstract methods?

preethi kumar
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Joined: Jun 04, 2010
Posts: 50
can anyone tell me?
Hunter McMillen
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Joined: Mar 13, 2009
Posts: 492

Abstract classes can't be instantiated(you can't create objects of their type), but they can be subclassed. Which means that another class could inherit all of its methods and attributes; whether those methods are abstract or not is up to the designer.

Example: Assume Java doesn't actually have a Math class


The PI constant in the shape class can be used by the Circle class. This is a poor example because Java provides a Math class that holds constants like PI.

Sun examples:
http://java.sun.com/docs/books/tutorial/java/IandI/abstract.html

Hunter


"If the facts don't fit the theory, get new facts" --Albert Einstein
preethi kumar
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Joined: Jun 04, 2010
Posts: 50
we could have done the same thing without declaring the shape class abstract right?

whats is the difference it made?
Hunter McMillen
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Joined: Mar 13, 2009
Posts: 492

You could have yes. But in this case Shape was abstract because you wouldn't just want to create a generic Shape object. You wouldnt know how to find the volume of a "Shape", or its circumference, etc..


Hunter
Bear Bibeault
Author and ninkuma
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Joined: Jan 10, 2002
Posts: 61201
    
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Remember, just because you can do something doesn't mean that you should.


[Asking smart questions] [Bear's FrontMan] [About Bear] [Books by Bear]
marc weber
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Joined: Aug 31, 2004
Posts: 11343

Bear Bibeault wrote:Remember, just because you can do something doesn't mean that you should.

I can reply to this.


"We're kind of on the level of crossword puzzle writers... And no one ever goes to them and gives them an award." ~Joe Strummer
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preethi kumar
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Joined: Jun 04, 2010
Posts: 50
thank you so much
preethi kumar
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Joined: Jun 04, 2010
Posts: 50
ya marc you can reply
 
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