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abstract class without abstract methods

Posted on 2011-09-07
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i would like to now about
abstract class without abstract methods

When, why, how, where we use it. I was under impression that abstract should have atleast 1 abstract method in it. I was not clear on this concept. thanks in advance
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Question by:gudii9
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for_yan earned 2000 total points
ID: 36495636

see here:
http://stackoverflow.com/questions/4811678/defining-an-abstract-class-without-any-abstract-methods

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Of course.

Declaring a class abstract only means that you don't allow it to be instantiated on its own.

Declaring a method abstract means that subclasses have to provide an implementation for that method.

The two are separate concepts, but obviously you can't have an abstract method in a non-abstract class.
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by:for_yan
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http://www.codestyle.org/java/faq-Abstract.shtml#whynoabstract
Q: Why do we need abstract classes with no abstract methods?

    A: An abstract class without any abstract methods should be a rare thing and you should always question your application design if this case arises. Normally you should refactor to use a concrete superclass in this scenario.

    One specific case where abstract class may justifiably have no abstract methods is where it partially implements an interface, with the intention that its subclasses must complete the interface. To take a slightly contrived motoring analogy, a Chassis class may partially implement a Vehicle interface and provide a set of core methods from which a range of concrete Vehicle types are extended. Chassis is not a viable implementation of a Vehicle in its own right, so a concrete Car subclass would have to implement interface methods for functional wheels, engine and bodywork.
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by:for_yan
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SO when you declare such class you mean that those who woul use it can only extend it but cannot use it as it is.
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by:Kevin Cross
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This question has been classified as abandoned and is closed as part of the Cleanup Program. See the recommendation for more details.
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