In java adjectives ending in -able are interfaces Serializable
, Comparable
etc... So why is Throwable
a class? Wouldn't exception handling be easier if Throwable
were an interface? (Edit: e.g. Exception classes don't need to extend Exception/RuntimeException.)
Obviously, changing it now is out the question. But could it be made abstract? Wouldn't that avoid the bad practice of throw new Throwable()
;
Here's how James Gosling explained his decision:
Java Developer Connection Program: Why is
Throwable
not an interface? The name kind of suggests it should have been. Being able tocatch
for types, that is, something liketry {} catch (<some interface or class>)
, instead of only classes. That would make [the] Java [programming language] much more flexible.James Gosling: The reason that the
Throwable
and the rest of those guys are not interfaces is because we decided, or I decided fairly early on. I decided that I wanted to have some state associated with every exception that gets thrown. And you can't do that with interfaces; you can only do that with classes. The state that's there is basically standard. There's a message, there's a snapshot, stuff like that — that's always there. and also, if you makeThrowable
an interface the temptation is to assign, to make any old object be aThrowable
thing. It feels stylistically that throwing general objects is probably a bad idea, that the things you want to throw really ought to be things that are intended to be exceptions that really capture the nature of the exception and what went on. They're not just general data structures.