As others have mentioned, an interface is a contract and any possible exception that may be thrown needs to be explicitly defined, that's why checked exceptions

As others have mentioned, an interface is a contract and any possible exception that may be thrown needs to be explicitly defined, that's why checked exceptions exists. However, there is an exception (pun intended) to this: inline lambdas. You can use lambdas as variables, pass them as parameters, etc. And it makes sense for them to retain the interface if needed, but (at least on java) when you are doing a .map(v->parseInt(v)) checked exceptions can't escape the lambda, and that's probably the worst problem of java lambdas. You can avoid this with custom interfaces where the exception is a generic parameter, but sadly native ones aren't defined like this (yes, exceptions that a function throws can also be defined with generics, and the compiler will automatically use the more restrictive of the lambda code! )