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copied!<p>You are trying to abstract 2 things that is different. Is adding a <code>RentalItem</code> is same with adding a <code>MovieItem</code>? If yes then you can abstract the method. Otherwise, better not abstract it.</p> <p>EDIT: </p> <p>Maybe I am not clear with my statement. Now look at example of this code:</p> <pre><code>RentalItem rent = new RentalItem(); rent.AddItem(..params); </code></pre> <p>Is the usage of <code>AddItem</code> method in <code>RentalItem</code> class. Now for the MovieItem class:</p> <pre><code>MovieItem mv = new MovieItem(); mv.AddItem(..params); </code></pre> <p>Now looks fine. However, because <code>MovieItem</code> is inherited by <code>RentalItem</code>, we can implement it like this:</p> <pre><code>RentalItem item = new MovieItem(); item.AddItem(..params); </code></pre> <p>This comes the problem. We can see that the <code>MovieItem.AddItem</code> is different with <code>RentalItem.AddItem</code>, because it cannot be invoked by <code>RentalItem</code>, and both method accept different parameter. Now what we can do?</p> <p>First, if does not needed or if not logically same, let the <code>MovieItem</code> as a new class instead inherited from <code>RentalItem</code>.</p> <p>Second, if you need inheritance, let the <code>RentalItem</code> and <code>MovieItem</code> become only the entity with just properties and not method. And for handling the AddItem, you create another class like <code>RentalItemCollection</code> and <code>MovieItemCollection</code> which in logic does not has relation each other.</p>

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