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POCan generics allow the Java compiler to check the type of keys and values in a map?
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copied!<p>I am in a situation where I want to have a map where the keys are an interface class, and the corresponding value is a class which implements that interface. In other words the key and value type is related.</p> <p>My current implementation of the method which adds to the map, and gets an instance of the implementation class looks like:</p> <pre><code>// should be something like Class<T>, Class<? extends T> static Map<Class<?>, Class<?>> map = new HashMap<Class<?>, Class<?>> (); public static <T> void add(Class<T> interfaceT, Class<? extends T> implementationT) { map.put(interfaceT, implementationT); } public static <T> T get(Class<T> interfaceT) { // cast caused by definition not complete. Class<T> implementationT = (Class<T>) map.get(interfaceT); // try catch stuff omitted T t = implementationT.newInstance(); return t; } </code></pre> <p>My question is:</p> <p><em>Can</em> I define the "map" variable so the cast in the get(...) method is unneeded? I could not make the " new <code>HashMap<Class<T>, Class<? extends T>></code>()' work, so either it is impossible or I missed something fundamental :)</p> <p>Please advise :)</p> <hr> <p>Edit: It turned out that the asSubclass() method on Class did what I wanted :D</p> <pre><code>Class<?> rawClassFromMap = map.get(interfaceT); Class<? extends T> implementationT = rawClassFromMap.asSubclass(interfaceT); </code></pre> <p>It is fine that implementationT is of type "? extends T" as I just need a T object returned.</p> <p>I like generics. Reminds me of Haskell...</p>

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