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POAny good examples of inheriting from a concrete class?
 

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  1. POAny good examples of inheriting from a concrete class?
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    <p><strong>Background:</strong> </p> <p>As a Java programmer, I extensively inherit (rather: implement) from interfaces, and sometimes I design abstract base classes. However, I have never really felt the need to subclass a concrete (non-abstract) class (in the cases where I did it, it later turned out that another solution, such as <a href="http://en.wikipedia.org/wiki/Delegation_pattern" rel="nofollow noreferrer">delegation</a> would have been better).</p> <p>So now I'm beginning to feel that there is almost no situation where inheriting from a concrete class is appropriate. For one thing, the <a href="http://en.wikipedia.org/wiki/Liskov_substitution_principle" rel="nofollow noreferrer">Liskov substitution principle</a> (LSP) seems almost impossible to satisfy for non-trivial classes; also <a href="https://stackoverflow.com/questions/269496/inheritance-vs-aggregation">many</a> other <a href="https://stackoverflow.com/questions/3887871/is-inheritence-of-concrete-classes-evil">questions</a> here seem to echo a similar opinion.</p> <p><strong>So my question:</strong> </p> <p>In which situation (if any) does it actually make sense to inherit from a concrete class? Can you give a concrete, real-world example of a class that inherits from another concrete class, where you feel this is the best design given the constraints? I'b be particularly interested in examples that satisfy the LSP (or examples where satisfying LSP seems unimportant).</p> <p>I mainly have a Java background, but I'm interested in examples from any language.</p>
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      1. POAny good examples of inheriting from a concrete class?
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    1. COWhen coding a hierarchy of classes, such as the trivial Dog extends Animal. I usually use inheritance extensively when coding datamodels. For me, modelling real life things is when inheritence comes to play.
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      1. USMister Smith
    2. COAssuming I got what you mean by delegation: One good reason for using subclasses is that it's such a big headache to define classes that delegate all the methods of an interface to another class - in Java and many other OOP languages too. So the common practice to accumulate more and more interfaces in classes by building a hierarchy in which each subclass implements another interface that the base class did not. Ideally, though, it makes heaps more sense to delegate interfaces.
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      1. POAny good examples of inheriting from a concrete class?
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    3. COThere is the pathological case of inheriting from Object ...
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      1. USJens Schauder
 

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