5 ms·

I like checked exceptions. It's nice getting a reminder about issues I need to handle and its trivial to just get everything to pass on exceptions if that's th

• Quekid5 7y ago
  It's not trivial if you're forced to conform to an interface which has a narrower "throws" clause than what you need. It's an issue of contravariance vs. covariance. Implementations of an interface/superclass are typically more concrete, and so they need to be able to throw more more types of exceptions... but throws clauses work in the opposite way: You're only allowed to narrow them, not expand them in subclasses/implementations-of-interfaces. It's simply broken. EDIT: Just to add: What happens in practice is that either - you just give up and declare "throws Exception" on the interface (in which case: why bother? You might as well just remove checked exceptions at that point), or - you wrap checked exceptions in RuntimeException, but now you have a new problem: Consider a method that calls methods f and g where f declares a "throws Foo", but g doesn't declare any exceptions[0], but may throw Foo's at runtime by wrapping. Now you're totally screwed, because a "catch Foo" will not match exceptions from g. The Guava people have written a whole Throwables utility class to help with this, but using that consistently requires discipline that no team can handle, and it only handles a small subset of the problem. This is just a small sample of the problems with checked exceptions in Java. [0] g may be used in contexts where it's not "allowed" to declare checked exceptions in a throws clause, e.g. lambdas or just higher-order functions in general.