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PO
 

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    <p>Personally I think it is a code smell.</p> <p>Like you say, unless they have some base functionality - which they don't, they should be abstract, forcing derived classes to provide implementation.</p> <p>If some derived classes shouldn't have an implementation for these methods, then there's probably something wrong with the design.</p> <p>Consider this:</p> <pre><code>public abstract class Animal { public abstract string Speak(); } public class Dog : Animal { public override string Speak() { Console.WriteLine("Woof"); } } public class Cat : Animal { public override string Speak() { Console.WriteLine("Meow"); } } </code></pre> <p>All fine so far, but what if you want to add an animal that doesn't speak?</p> <pre><code>public class Ant : Animal { public override string Speak() { // do nothing - ants don't speak. } } </code></pre> <p>This in my opinion is bad. Someone might do this (what you have described).</p> <pre><code>public abstract class Animal { public string Speak() { // not abstract because not all derived animals speak. } } </code></pre> <p>This in my opinion, is better, but still not great. What I would like to see in this situation is either Speak be moved to an interface and only the animals that can speak implement it, or something like this.</p> <pre><code>public abstract class Animal { } public abstract class Mammal : Animal { public abstract string Speak(); } public class Dog : Mammal { public override string Speak() { Console.WriteLine("Woof"); } } public class Cat : Mammal { public override string Speak() { Console.WriteLine("Meow"); } } public class Ant : Animal { } </code></pre>
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    1. POIs there any reason for an empty concrete method in an abstract class?
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    1. COLeaving methods empty in super classes bothers me as well. However, I think I'd have to accept this idea as legitimate and agree with Andrés Fortier's answer. E. g.: What if I had a class that holds a collection of Animal and I'd like to execute some methods on them, Speak() being one of them, if the corresponding Animal would be a Mammal. Does this mean I'd have to use an instanceof or would I have to hold a redundant collection with Mammals? I don't like both of these ideas and would stay with the empty Speak()-method in the Animal class.
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    2. COISpeak interface would be the way to go then.
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    3. COThis fails, if the methods I'd like to execute are among Animal's definition and does not only consist of the speak()-method. Say there's an eat()-method. I want to execute eat and speak. I then have to choose one of the constructs I mentioned before.
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