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    <p>If you keep in mind fundamental difference between interfaces and classes it will make it easier to decide which one to use. The difference is that interfaces represent just a protocol (usually behavioral) between objects involved, while abstract classes represent some unfinished constructions that involve some parts (data). In car example, interface is essentially a blueprint for the generic car. And abstract class would be like prefabricated specific model car body that needs to be filled with remaining parts to get final product. Interfaces don't even have to be in Java - it will not change anything - still blueprint.</p> <p>Typically you would use abstract class within your specific implementation framework to provide its consumers with some basic functionality. If you just state that you never use abstract class in favor of interface - it's plain wrong from practical standpoint. What if you need 10 implementations of the same interface with 90% of the same code. Replicate code 10 times? Ok, may be you would use abstract class here but put interface on top of it. But why would you do that if you never intend to offer your class hierarchy to external consumers? I am using word external in very wide sense - it can be just different package in your project or remote consumer.</p> <p>Ultimately, many of those things are preferences and personal experiences, but I disagree with most blanket statements like <code>extends is evil</code>. I also prefer not to use extra classes (interfaces or abstract) unless it is required by specific parts of the design.</p> <p>Just my two cents.</p>
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    1. POHow to move away from Inheritance
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    1. USAlex Gitelman
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    1. COThanks for your answer Alex, you have a good way of making concepts transparent, it really made it clearer for me. I agree that article is too radical, probably to catch some attention :)
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      1. USPaulo Ricca
 

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