Those are from java 1.0 and thus don't appear to be relevant to the part of the discussion I think this part of the thread is about (namely: "Why doesn't java crib well designed features from other languages?").
> Java went with checked exceptions and nowadays they are almost universally ignored by developers.
They aren't.
Note that other languages invented for example 'Either' which is a different take on the same principle, namely: Explicit mention of all somewhat expectable alternative exit conditions + enforcing callers to deal with them, though also offering a relatively easy way to just throw that responsibility up the call chain.
The general tenet (lets lift plausible alternate exit conditions into the type system) is being done left and right.
Java could do something similar but they have enough promise types already.
The problem with Java is that they haven’t added the syntax to make dealing with those errors easy. It’s boiler plate hell.
That’s not the only issue, though: Java also shunts both checked and unchecked exceptions through the same mechanism, conflating them. It’s no wonder that Java’s problematic implementation of checked exceptions has poisoned people against the concept.
I think streams are a great example of what I was saying about Java failing to take advantage of coming last. Scala (probably among others, but Scala was right there on the JVM) had already demonstrated that it was possible to enable simple, readable code for simple use cases, while also enabling complex and powerful usage. And the experience of Scala had shown that there's little demand for parallel collections outside of extremely niche use cases where people tend to use specialized solutions anyway. Somehow Java, with this example staring them in the face, managed to get the worst of both worlds.
I always believed it was a major plus point for Java compared to other languages. I am even surprised to hear otherwise. How should parallel processing of streams work in your opinion, then ? Just saying it be unsupported would be laughable considering hardware today.
I would rate this feature 9/10. The fact that the author has rated it 1/10, shows he hasn't really worked on large, parallel processing of data - in Java anyways.
A lot of code that throws checked exceptions is simply dangerous to use with Java streams because the execution order of stream operation is not obvious and possibly non-deterministic. For this reason, streams were never intended to also handle errors. Reactive frameworks are much better at that.
The UncheckedIOException is for situations where you really cannot throw a checked exceptions, such as inside an iterator. Which might lead to ugly surprises for the API user;
From the type system PoV, they could have just written something like `interface Runnable<X> { void run() throws X; }` and now `forEach` would have been written like `<X> void forEach(Runnable<X> r) throws X`. And repeat that for all stream operations, promoting `X` everywhere, so if your mapper function throws SQLException, the whole pipeline will throw it.
It even works today with some limitation (there's no way for `X` to get value of `SQLException|IOException` union type), but with some generic improvements it could work.
But they decided to not touch this issue at all. So now people will fool compiler with their tricks to throw checked exceptions like unchecked (or just wrap them with UncheckedXxxException everywhere, I prefer that approach).
Checked exceptions are an awesome feature that more languages should have. Just like static typing is a good thing because it prevents errors, checked exceptions are a good thing because they prevent errors.
Java's implementation of checked exceptions has some issues, though.
* "Invisible control flow", where you can't tell from the call site whether or not a call might throw (you need to check the signature, which is off in some other file, or perhaps visible in an IDE if you hover).
* Java has both checked and unchecked exceptions, but they go through the same try-catch mechanism, failing to make a clean distinction between recoverable errors and unrecoverable bugs. (In e.g. Rust and Go, recoverable errors go through return values but unrecoverable errors go through panics.)
In the end, Java's exception design simultaneously requires a lot of effort to comply with, but makes it difficult to understand when you've successfully locked things down.
Never found this this to be a problem. It is really common to all implementations of exceptions, not just checked ones. And when you write code the compiler will yell at you. In monadic code,
People are used to that, and one common strategy is to not worry too much about exceptions and then wrap a big `try` block around everything near the outer boundary of your code. It’s good enough for many purposes and yields a high initial development velocity, but is comparatively fragile.
With Languages like Rust, Go, and Swift, only unrecoverable errors trigger the panic mechanism. Every call site where a recoverable error may occur is identifiable — in Rust via Result, `unwrap()`, the `?` operator, etc, in Go via returned Err (though unlike Rust you can discard them silently), and in Swift via the `try` operator.
You can still develop quickly by just unwrapping every Result, but unlike languages with invisible control flow, you can easily audit the codebase and go back to harden every site where a recoverable error may occur — yielding a level of robustness which is difficult to achieve in languages with unchecked exceptions.
> failing to make a clean distinction between recoverable errors and unrecoverable bugs
Recoverability is context specific. One persons panic may just be another error case for someone else. I think this is one thing that programmers miss when talking about this topic. It is really up to the caller of your function if something should panic. You can’t make that decision for them.
> One persons panic may just be another error case for someone else.
We can make a strong distinction between recoverable errors (e.g. this I/O operation may fail) versus unrecoverable errors that may leave the process in an unsound state, such as divide-by-zero or out-of-bounds array access[1].
There are some problem domains where even unrecoverable errors are not allowable, and programmers in those domains have to grapple with the panic mechanism.
But for the rest of us, it is useful to be able to distinguish between recoverable and unrecoverable errors — and to know how we have handled all possible sites which could result in recoverable errors.
[1] Joe Duffy explains it well: https://joeduffyblog.com/2016/02/07/the-error-model/#bugs-ar...
It might only be one language, but it’s a pretty big one
Eg, mutable state capture in lambdas is largely restricted because of the thought that people would use parallel threads within the stream processing blocks. That decision lead to lots of ugly code, IMO.
I've also never seen a need to try to parallelize a simple stream processing step.
There might be use-cases, but I've yet to encounter them.
And when I need parallel computation, I can just use good old ExecutorService. Few more lines, but that's OK for a task that arises once in a 10 years.
Modules absolutely achieved their primary goal: stopping libraries from accessing JDK internals without the application's knowledge. The ecosystem is slow on the uptake since split packages and access to internal APIs is endemic, but it is happening ever so slowly. I wish libraries could opt into not being part of the unnamed module.
Virtual threads were designed with explicit cooperation of the community, with the explicit goal of making it easy to switch as much existing code over to it as possible. I really don't understand the scepticism there. Most other languages went with promises or reactive streams because they were inspired by how functional programming languages do it.
The same way, caller can know which exceptions are really likely to happen in TypeScript, C++, Python. Or in modern Java which avoids checked exceptions anyway. By reading documentation or source code. That's perfectly fine and works for everyone.
And you highlighted one big issue with checked exceptions. You've claimed that those exceptions are "really likely to happen".
When I'm writing reading data from resource stream, the data that's located next to my class files, IO Exceptions are really unlikely to happen.
Another ridiculous example of this checked exception madness:
var inputStream = new ByteArrayInputStream(bytes);
var outputStream = new ByteArrayOutputStream();
inputStream.transferTo(outputStream); // throws IOException? wtf???
There's no correspondence between checked exceptions and likelihood of their occurence. NullPointerException probably happens more than any checked exception. The division between checked exceptions and unchecked exceptions is absolutely arbitrary and makes sense only at caller place, never in called function signature.
> Modules absolutely achieved their primary goal: stopping libraries from accessing JDK internals without the application's knowledge. The ecosystem is slow on the uptake since split packages and access to internal APIs is endemic, but it is happening ever so slowly. I wish libraries could opt into not being part of the unnamed module.
"Slow" is an understatement. I don't see this happening at all. Last time I tried to write very simple application with modules, I spent so many hours banging my head over various walls, that I probably will not do another attempt in a foreseeable future.
https://www.reddit.com/r/java/comments/1o37hlj/reopening_the...
And some people write code in Python which provides no automatic verification whatsoever.
Actually unchecked exceptions are very similar to dynamically typed languages. And that's fine. As Python and other languages proved by their mere existence: dynamic typing is not inherently bad. Sometimes it's good. I think that for error handling, it's good.
> Java class loaders can do anything including loading resources from the network. Which is admittedly not that common these days after the demise of applets.
Technically they can, but in my particular case I know very well, that my resources are residing inside of JAR file. And if that JAR file happened to reside on the failed HDD block, that's not going to be a recoverable error.
When we're talking about IO Exceptions, it's almost always failed operation which requires complete abort. It's either failed hardware, or, typically, disconnected client. Can't do much about it, other than clean up and proceed to the next client.
And the same could be said about SQL Exceptions. Like 99% of SQL exceptions are application bugs which are not going to be handled in any way other than wind up and return high level HTTP 500 error or something like that. There are cases when SQL exception should be handled, but those are rare. Yet JDBC developers decided that programmers must execute error handling rituals on every call site.
> The NullPointerException indicates a bug in the application. By the very reason it occurs, the current thread cannot continue execution normally.
That's not exactly true. In JVM, NullPointerException is absolutely well defined and you can continue execution after catching it. You might suspect, that logical application state is corrupted, but sometimes you know well that everything's fine (and in most cases you hope that everything's fine, if your Spring MVC handler threw NPE, Spring is not going to crash, it'll continue to serve requests). It's not C++ with its undefined stuff. JVM is pretty reliable when it comes to every error, including NPE, stack overflow or OOM. Latter is special, because even handling error might prove challenging, when memory allocations fail, but JVM will not hang up or crash.
Python is a language with almost no static validation whatsoever. It would be very odd if it cared about checked exceptions. This dynamism makes big Python code bases infuriating to work with.
> When we're talking about IO Exceptions, it's almost always failed operation which requires complete abort. It's either failed hardware, or, typically, disconnected client. Can't do much about it, other than clean up and proceed to the next client.
If this is the case then the solution is to add it to the `throws` list.
> That's not exactly true. In JVM, NullPointerException is absolutely well defined and you can continue execution after catching it.
Why would I catch a NullPointerException instead of fixing my application? The JVM is indeed completely fine, but processing still cannot continue because that code simply does not exist.
For example they used checked exceptions. Those definitely do not seem like proven feature. C++ has unchecked exceptions. Almost every other popular language has unchecked exceptions. Java went with checked exceptions and nowadays they are almost universally ignored by developers. I'd say that's a total failure.
Streams another good example. Making functional API for collections is pretty trivial. But they decided to design streams for some kind of very easy parallelisation. This led to extremely complicated implementation, absurdly complicated. And I've yet to encounter a single use-case for this feature. So for very rare feature they complicated the design immensely.
Modules... LoL.
We will see how green threads will work. Most languages adopt much simpler async/await approach. Very few languages implement green threads.