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Comment by rowls66 | Hacker News Reader

That is true, so the library should throw the checked exception, and if the caller has no way to handle it, it should wrap the checked exception in an unchecked exception and throw the unchecked exception. Not too hard, and library clients that can handle some checked exceptions will be able to.

I hate libraries that only throw unchecked exceptions. It seems easier initially, but makes writing correct code more difficult.

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> If the caller has no way to handle it, it should wrap the checked exception in an unchecked exception and throw the unchecked exception.

Not you have a new problem: How is the code calling the caller supposed to know about that exception? You can't even catch it (even if you know about it!) using normal try-catch because what you have to do is catch the wrapper exception and then check inside that for the exception type you expect via instanceof.

Checked exceptions (at least as implemented in Java) are horrible for the composability of code wrt. error handling.

That is why most libraries eschew checked exceptions these days. Unfortunately, large bits of the standard library in Java forces their hand wrt. re-wrapping stuff like InterruptedException and IOException and the like.

(Not to mention, most of the time you really shouldn't be catching exceptions in very small scopes or at the very highest level in your code. Involving every single layer in between is madness.)

The error here is not that they are wrapping the exception necessarily. It is that they re-threw it as an unchecked exception. I strongly believe the only good use of unchecked exceptions is if the code should do the closest reasonable thing to crash safely. Everything should be clearly communicated to the callers so they can make good decisions about what to handle here and what to pass up the chain.

If the complaint is that you then have too many different unchecked exceptions perhaps the error domain has been improperly modeled and you are getting a clue that the system is poorly designed.

> The error here is not that they are wrapping the exception necessarily. It is that they re-threw it as an unchecked exception.

You often don't have a choice. Think of generic interfaces -- for example the humble apply method on https://docs.oracle.com/javase/8/docs/api/java/util/function... .

If you have a Function which needs to do some interruptible work you cannot throw InterruptedException -- you must wrap it. This is a fundamental design flaw in Java's exception system and cannot be handwaved away just by saying that Function is badly designed. This problem is pervasive.

The ultimate problem here is one of variance -- throws clauses have the opposite variance rules from method implementations: Subclasses (whether of interfaces or classes) frequently need to more than could be foreseen by the implementor of the interface, so they need to be able to throw "more things", but checked exception clauses explicitly disallow widening the set of thrown exceptions in subclasses (for obvious reasons -- since a FooImpl can be used a runtime where a Foo is expected).

This is a fundamental flaw that was overlooked in the checked exceptions design and there's no fixing it now.

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