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    <p><strong>EDIT:</strong></p> <p>I have taken the body of code for each class out - If you want to see my answer, have a look at the edit revisions :)</p> <p>First off we define the <a href="http://msdn.microsoft.com/en-us/library/ms173156.aspx" rel="noreferrer">interface</a></p> <pre><code>public interface IAnimal { string WhatAmI { get; } string WhatIsMyName { get; } } </code></pre> <p>Any class that implements this interface must implement these properties. An interface is like a contract; a class implementing an interface agrees to provide an implementation of the interface's methods, properties events or indexers.</p> <p>Next, we need to define your abstract Animal class</p> <pre><code>public abstract class Animal : IAnimal { //Removed for Training, See Edit for the code } </code></pre> <p>The fact that the class is <a href="http://msdn.microsoft.com/en-us/library/sf985hc5(VS.71).aspx" rel="noreferrer">abstract</a> indicates that the class is intended only to be a base class for other classes. We have implemented both properties of the interface and also have a private field to store the animal name. In addition, we have made the <code>WhatAmI</code> property accessor abstract so that we can implement our own specific property accessor logic in each derived class and have also defined a constructor that accepts a string argument and assigns the value to the <code>_name</code> private field.</p> <p>Now, let's define our <code>Cat</code> and <code>Dog</code> classes</p> <pre><code>public class Dog : Animal { //Removed for Training, See Edit for the code } public class Cat : Animal { //Removed for Training, See Edit for the code } </code></pre> <p>Both classes inherit from <code>Animal</code> and each has a constructor that defines a string argument and passes that argument as a parameter to the base constructor. In addition, each class implements it's own property accessor for <code>WhatAmI</code>, returning a string of their type, respectively.</p> <p>For the rest of the code</p> <pre><code>public class Program { public static void DescribeAnimal(IAnimal animal) { Console.WriteLine("My name is {0}, I am a {1}", animal.WhatIsMyName, animal.WhatAmI); } static void Main(string[] args) { Dog mydog = new Dog("Spot"); Cat mycat = new Cat("Felix"); DescribeAnimal(mydog); DescribeAnimal(mycat); Console.ReadKey(); } } </code></pre> <p>the static method <code>DescribeAnimal</code> accepts an <code>IAnimal</code> as an argument and writes out the values returned by the <code>WhatIsMyName</code> and <code>WhatAmI</code> property accessors for the passed in <code>IAnimal</code>. </p> <p>Since <code>Animal</code> implements <code>IAnimal</code> and both <code>Dog</code> and <code>Cat</code> inherit from <code>Animal</code>, any <code>Cat</code> or <code>Dog</code> object can be passed as a parameter to the <code>DescribeAnimal</code> method.</p> <p>I hope that I have explained this clearly, If anyone feels my choice of words needs tightening up, please comment and I will be happy to edit my answer.</p>
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    1. POCan you help me understand in a practical example the usage abstract classes vs interfaces?
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    1. POCan you help me understand in a practical example the usage abstract classes vs interfaces?
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    1. COhonestly, I've been avoiding reading all your commentary in full since I don't like "reading" the answer to my project, but fyi the link you gave to MSDN gave "sample" code that has helped me move my project along thanks for the help there!
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    2. COgood stuff :) Let me know if you want me to delete my answer, or leave it to come back to once you've got your solution
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    3. COno, i appreciate the help, i'll review it after i'm done on my side to see if i've got the idea right. this has actually been much harder for me to understand than most concepts... the textbook really sucks, i have a high reading level, but its so dry, i get 1-2 paragraphs before losing focus
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