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POAt runtime, find all classes in a Java application that extend a base class
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  1. POAt runtime, find all classes in a Java application that extend a base class
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    copied!<p>I want to do something like this:</p> <pre><code>List&lt;Animal&gt; animals = new ArrayList&lt;Animal&gt;(); for( Class c: list_of_all_classes_available_to_my_app() ) if (c is Animal) animals.add( new c() ); </code></pre> <p>So, I want to look at all of the classes in my application's universe, and when I find one that descends from Animal, I want to create a new object of that type and add it to the list. This allows me to add functionality without having to update a list of things. I can avoid the following:</p> <pre><code>List&lt;Animal&gt; animals = new ArrayList&lt;Animal&gt;(); animals.add( new Dog() ); animals.add( new Cat() ); animals.add( new Donkey() ); ... </code></pre> <p>With the above approach, I can simply create a new class that extends Animal and it'll get picked up automatically.</p> <p>UPDATE: 10/16/2008 9:00 a.m. Pacific Standard Time:</p> <p>This question has generated a lot of great responses -- thank you. From the responses and my research, I've found that what I really want to do is just not possible under Java. There are approaches, such as ddimitrov's ServiceLoader mechanism that can work -- but they are very heavy for what I want, and I believe I simply move the problem from Java code to an external configuration file. </p> <p>Another way to state what I want: a static function in my Animal class finds and instantiates all classes that inherit from Animal -- without any further configuration/coding. If I have to configure, I might as well just instantiate them in the Animal class anyway. I understand that because a Java program is just a loose federation of .class files that that's just the way it is.</p> <p>Interestingly, it seems this is <a href="http://my.safaribooksonline.com/0596003390/csharpckbk-CHP-12-SECT-8" rel="noreferrer">fairly trivial</a> in C#.</p>
 

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