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POTrying to build an extensible data object and adapter pattern in Java
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copied!<p>I'm trying to build an SDK using an adapter pattern. Here's what I've got so far:</p> <pre><code>interface Adapter<T> { void doWork(WorkUnit<T> unit); Class<T> getT(); } class WorkUnit<T> { public int getId() { ... } public T getExtras() { ... } } class OldWorkUnit { public <T> void setExtra(T data) { /* Store data in Map<Class, Object> */ } public <T> WorkUnit<T> toNewWorkUnit(Adapter<T> adapter) { /* Map.get(adapter.getT()) */ } } </code></pre> <p>There's a good amount of generics in there, but I can't know T at compile time, and there may be multiple Adapters, all with different types of T. This is meant to be exposed to third parties, so I also need as little implementation as possible in the interface implementation, and it has to be an interface (no abstract class).</p> <p>Now I want to take this and call doWork with a WorkUnit. My first pass at the code looks like this:</p> <pre><code>class FooAdapter implements Adapter<FooWorkUnit> { ... } OldWorkUnit w = new OldWorkUnit(); w.setExtra(new FooWorkUnit()); Adapter<?> a = new FooAdapter(); WorkUnit<?> unit = w.toNewWorkUnit(a); a.doWork(unit); </code></pre> <p>Uh oh, that doesn't compile:</p> <pre><code>The method doWork(WorkUnit<capture#2-of ?>) in the type Adapter<capture#2-of ?> is not applicable for the arguments (WorkUnit<capture#4-of ?>) </code></pre> <p>I know that the WorkUnit generic argument is the same type as the Adapter.doWork() generic argument, but without knowing the type I can't cast it appropriately. </p> <p>So is there a way to work my way through this?</p>

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