RFR: 8305457: Implement java.io.IO [v3]

[Pavel Rappo]

I don't remember it being considered, but I think it falls outside the scope of JEP 477 (emphasis mine):

> We achieve this effect by declaring a new top-level class in the java.io package named, simply, IO. It declares the above three static methods for **textual** I/O with the console, and nothing else.

java.io.IO is closely related to java.io.Console, which provides access to a terminal in a more or less canonical mode to read and write _strings_. While it might be useful for Console to separately provide access to a terminal in the raw mode, I'm not sure how often developers, let alone on-ramp developers, need it. In my experience, programming games, such as those you mentioned, is better introduced with GUI, where they have java.awt.event.KeyListener.

-Pavel

> On 8 May 2024, at 14:59, Olexandr Rotan <rotanolexandr842 at gmail.com> wrote:
> 
> Has it been considered to add a readKey() method to IO class? In my experience, it is pretty commonly used by beginners when they write things like console games (snake, catcher game etc.). I am aware there is System.in.read() method, but since we decided to promote some methods to separate methods in IO class, maybe readKey() or simple read() should also be considered?
> 
> On Wed, May 8, 2024 at 4:16 PM Pavel Rappo <prappo at openjdk.org> wrote:
> On Wed, 8 May 2024 10:31:59 GMT, Jaikiran Pai <jpai at openjdk.org> wrote:
> 
> >> If we specify that, it would be very much unlike all other `Console` methods that are covered by this:
> >> 
> >>     * Unless otherwise specified, passing a {@code null} argument to any method
> >>     * in this class will cause a {@link NullPointerException} to be thrown.
> >
> > I haven't given it a try, but a brief look at the code suggests that if the console implementation backed by JLine gets used, then a `null` prompt may not generate a `NullPointerException` (since JLine appears to allow `null`) whereas if the internal JDK console implementation gets used then a `NullPointerException` will get thrown. If the expectation is to disallow a `null` prompt, then perhaps `Objects.requireNonNull(prompt)` before we hand off to the underlying console implementations might be required.
> 
> Good catch! `jdk.internal.org.jline.JdkConsoleProviderImpl.JdkConsoleImpl.readln(null)` does not throw `NullPointerException` (NPE), which it must. I'll fix the bug and add a test.
> 
> Speaking of NPE. The newly added `Console.print` and `Console.println` methods do not throw NPE if passed null. While that's how it should be, they don't specify that, so the class-level NPE clause applies:
> 
>     * Unless otherwise specified, passing a {@code null} argument to any method
>     * in this class will cause a {@link NullPointerException} to be thrown.
>     ...
>     public sealed class Console implements Flushable permits ProxyingConsole {
> 
> I'll fix that.
> 
> We should also specify NPE (or absence thereof) on methods of `IO`. Otherwise, this package clause applies:
> 
>     * Unless otherwise noted, passing a {@code null} argument to a constructor or
>     * method in any class or interface in this package will cause a
>     * {@code NullPointerException} to be thrown.
>     ...
>     package java.io;
> 
> @stuart-marks speaking of exceptions. Do we need to add explicit `@throws` tag to `IO` methods?
> 
>     @throws {@code IOError} if {@code System.console()} returns {@code null}
> 
> While it would make sense, it would also look superfluous: we already specify that error condition in the class comment and then in every method's main description. Do we need to add one more note on `IOError`?
> 
> -------------
> 
> PR Review Comment: https://git.openjdk.org/jdk/pull/19112#discussion_r1594013064