Java generics: creating collections of class objects extending Throwable

Question

Why does the first line work, but the second one doesn't?

Collection<Class<? extends Throwable>> exs =
    new ArrayList<Class<? extends Throwable>>() {{ add(MyOwnException.class); }};
Collection<Class<? extends Throwable>> exs = Arrays.asList(MyOwnException.class);

Answer 1

The reason it's an error is that java is inferring the wrong type, but you can make it compile, without casting, by specifying the type in the call to the typed method Arrays.asList():

Collection<Class<? extends Throwable>> exs 
    = Arrays.<Class<? extends Throwable>>asList(Exception.class); // compiles

Without specifying the type, java infers the element type of the collection to be Class<Exception>, which is not assignable to Collection<Class<? extends Throwable>>.

Remember with generics that if B extends A, List<B> does not extend List<A>.