I understand mostly everything you say except for why there's any motivation to introduce more headaches in the form of a new Throwable interface, forcing people to become acquainted with interfaces before they can throw an exception. Under the assumption that we want to
Not true, because the built-in Exception class would remain, and implement the required Interface(s). This would allow the designer to either use Exception as base of his hierarchy, of use his own Throwable-derived class instead.
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Ard