Why doesn't Java allow generic subclasses of Throwable? - Stack Overflow

As mark said, the types are not reifiable, which is a problem in the following case:

try {
   doSomeStuff();
} catch (SomeException<Integer> e) {
   // ignore that
} catch (SomeException<String> e) {
   crashAndBurn()
}

Both SomeException<Integer> and SomeException<String> are erased to the same type, there is no way for the JVM to distinguish the exception instances, and therefore no way to tell which catch block should be executed.

Read full article from Why doesn't Java allow generic subclasses of Throwable? - Stack Overflow