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copied!<p>It is kind of silly. It would have been better, for most use cases, if <code>x.getClass()</code> returns <code>Class<? extends X></code>, instead of the erased <code>Class<? extends |X|></code>.</p> <p>The erasure is the cause of loss of information, making your code, apparently safe, fail to compile. <code>t.getClass()</code> returns <code>Class<? extends |T|></code>, and <code>|T| = Number</code>, so it returns <code>Class<? extends Number></code>.</p> <p>The erasure (mandated by the language spec) is to maintain theoretical correctness. For example</p> <pre><code>List<String> x = ...; Class<List> c1 = x.getClass(); // ok Class<List<String>> c2 = x.getClass(); // error </code></pre> <p>Although c2 seems very reasonable, in Java, there is really no such class for <code>List<String></code>. There is only the class for <code>List</code>. So allowing c2 would be, theoretically incorrect.</p> <p>This formality created lots of problem in real world usages, where programmers can reason that <code>Class<? extends X></code> is safe for their purposes, but have to cope with the erased version.</p> <p>You can simply define your own <code>getClass</code> that returns the un-erased type</p> <pre><code>static public <X> Class<? extends X> getFullClass(X x) return (Class<? extends X>)(Class) x.getClass() ; <T extends Number> void foo(T t) { Class<? extends T> klass = getFullClass(t); } </code></pre>

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