why is java.lang.Throwable a class?

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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 to catch for types, that is, something like try {} 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 make Throwable an interface the temptation is to assign, to make any old object be a Throwable 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.

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