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POPossibly recursive Java generics between two classes
 

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    <p>I'm attempting to produce some classes to control a model-view-presenter application. I've come up with the following definitions, but am struggling to avoid recursive generics.</p> <pre><code>public abstract class Presenter&lt;V extends View&lt;...?&gt;&gt; { protected V view; public Presenter(V view) { this.view = view; } // ... } public abstract class View&lt;P extends Presenter&lt;...?&gt;&gt; { protected P presenter; // ... } </code></pre> <p>I wanted to enforce a mutual relationship between the two classes. The idea being that I could instantiate a Presenter for a particular View, with both classes relying on useful methods defined in the abstract base classes, yet both knowing exactly what subclass of the counterpart abstract class is in use.</p> <p>My issues is the defining the <code>..?</code> part of the code. I can't see a way to avoid a recursive situation, such as:</p> <pre><code>public abstract class View&lt;P extends Presenter&lt;V&gt;, V extends View&lt;Q&gt;, Q extends...&gt; </code></pre> <p>and even that definition is not consistent, as the View class now takes two generic parameters... mass confusion.</p> <p>I basically wanted to avoid the classes being littered with references to the abstract class type, necessitating lots of casting throughout the concrete implementations, as below:</p> <pre><code>// simpler option public abstract class Presenter { protected View view; public Presenter(View view) { this.view = view; } } public class FooPresenter extends Presenter { public FooPresenter(BarView view) { super(view); } public someMethod() { ((BarView) getView()).viewSpecificMethod(); } } </code></pre> <p>Each concrete implementation of these classes would need to constantly cast from the abstract type to the type it "knows" is in use.</p>
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