Program logic bugs vs input/environmental errors (checked exceptions)

[Bruno Medeiros via Digitalmars-d]

On 29/09/2014 20:28, Sean Kelly wrote:
> Checked exceptions are good in theory but they failed utterly in
> Java.  I'm not interested in seeing them in D.

That is the conventional theory, the established wisdom.
But the more I become experienced with Java, over the years, I've become 
convinced otherwise.

What has failed is not the concept of checked exceptions per se, but 
mostly, the failure of Java programmers to use checked exceptions 
effectively, and properly design their code around this paradigm.

Like Jeremy mentioned, if one puts catch blocks right around the 
function that throws an exception, and just swallow/forget it there 
without doing anything else, then it's totally the programmers fault for 
being lazy.

If one is annoyed that often, adding a throws clause in a function will 
require adding the same throws clause function to several other 
functions, well, that is editing work you have to accept for the sake of 
more correctness. But also one should understand there are ways to 
mitigate this editing work:

First point is that in a lot of code, is better to have a function throw 
just one generic (but checked) exception, that can wrap any other 
specific errors/exceptions. If you are doing an operation that can throw 
File-Not-Found, Invalid-Path, No-Permissions, IO-Exception, etc., then 
often all of these will be handled in the same user-reporting code, so 
they could be wrapped under a single exception that would be used in the 
throws clause. And so the whole function call chain doesn't need to be 
modified every time a new exception is added or removed.

If you're thinking that means adding a "throws Exception" to such 
functions in Java, then no. Because this will catch RuntimeExceptions 
too (the unchecked exceptions of Java), and these you often want to 
handle elsewhere than where you handle the checked exceptions. In this 
regard, Java does have a design fault, IMO, which is that there is no 
common superclass for checked Exceptions. (there is only for unchecked 
exceptions)

The second point, is that even adding (or modifying) the throws clause 
of function signatures cause be made much easier with an IDE, and in 
particular Eclipse JDT helps a lot. If you have an error in the editor 
about a checked exception that is not caught or thrown, you can just 
press Ctrl-1 to automatically add either a throws clause, or a 
surrounding try-catch block.

-- 
Bruno Medeiros
https://twitter.com/brunodomedeiros