SimpleIO in JEP draft 8323335

Brian Goetz brian.goetz at oracle.com
Tue Feb 20 14:34:09 UTC 2024 

What you're really saying is "I want more than you're giving me."  And 
there's nothing wrong with wanting more.  You seem to have mostly 
accepted that the primitive is "read a line of input as a string", but 
it leaves you with a problem: you don't want to read strings, you want 
to read numbers.  That's all fine.

But the flip side of "this isn't good enough, give us more" is that if 
there isn't a "more" that is good enough to meet the the bar, you're 
going to get ... nothing.  It's a foundational design principle for Java 
(thanks James!) that if you don't know the right thing to do, then don't 
do anything (yet).  The alternatives that have been proposed (all of 
which we already went through before they came around again here) did 
not meet the bar.  This is what meets the bar.  It may not be as much as 
you want, but it is something, and it combines with all the other 
possible next steps.

As a teacher, you have many choices.  You can keep doing what you've 
been doing, teaching Scanner; many teachers will.  Or you could 
distribute your own library of convenience methods -- many teachers do.  
Or you could teach Integer::parseInt, which is messy, but has the 
benefit of being exactly as messy as the problem is -- which is also a 
useful lesson.  Or, or, or, or.

And if you don't like the magic static import, don't use it!  Tell your 
students to use `SimpleIO::readAStringPlease`.  We are not trying to 
create a beginners dialect here.

All of this is to say: we are not trying to put out a One True Only Way 
To Teach Java.  We're smoothing out the path in a way that admits many 
teaching paths, including ignoring all this stuff.  Is there more that 
could be done?  Of course.  And when we have a *good* candidate for what 
the next hundred feet of onramp looks like, we will proceed.  And I am 
confident that it will not conflict with these first hundred feet, 
because -- how could it?





On 2/20/2024 6:44 AM, Cay Horstmann wrote:
> I am one of the people who writes books for beginners. I have a whole 
> bunch of example programs that involve reading numbers. Professors 
> adopting my books have a ton of exercises that involve reading 
> numbers. I can't ignore reading numbers.
>
> I agree that input and println are reasonable primitives for 
> beginners, and that number parsing can be done in a separate step. But 
> if that parsing step is not simple for beginners, I don't think input 
> will find much use for beginners either.
>
> For my books, I need to decide what to do in the (n + 1)st edition. 
> Should I stick with
>
> Scanner in = new Scanner(System.in);
> ...
> System.out.print("How old are you? ");
> int age = in.nextInt();
>
> or switch to
>
> println("How old are you?");
> int age = in.nextInt();
>
> or go all the way to
>
> int age = Integer.parseInt(input("How old are you"));
>
> I have no conceptual problem with in.nextInt(). I need to explain 
> method calls early on, so that students can work with strings.
>
> With the new way, I have a different problem. Now I need to explain to 
> students that they can call an unqualified input, but parseInt needs 
> to be qualified. And I have to accelerate the coverage of static methods.
>
> As Brian says, there are too many conflicting goals.
>
> If the goal is simplicity and consistency, it would be more useful not 
> to use a magic static import. If SimpleIO.input is too long, it could 
> be IO.in, with IO in java.lang.
>
> If the goal is convenience, it would be better to have more magically 
> statically imported methods, in particular parseInt, parseDouble. Or 
> readAnInt, readADouble...
>
> Cheers,
>
> Cay
>
>
> On 19/02/2024 18.06, Brian Goetz wrote:
>> There's a reason there are so many opinions here: because the goals 
>> are in conflict.  Everyone wants simplicity, but people don't agree 
>> on what "simple" means.  (Cue the jokes about "I would simply not 
>> write programs with bugs.")
>>
>> Yes, getting numbers from the user is a basic task.  But it is not, 
>> in any way, simple!  Because reading numbers from the input is 
>> invariably complected with discarding things that are "acceptably 
>> non-numbery" (e.g., whitespace), which is neither simple nor usually 
>> terribly well documented.  We've all encountered the problem in many 
>> language runtimes where reading a number using the "friendly way" 
>> leaves the input in a state that requires fixing or yields surprises 
>> for the next operation.
>>
>> This is because reading a number from an input stream is not any sort 
>> of primitive; it is the composite of reading from the input, deciding 
>> what to skip, deciding when to stop reading, converting to another 
>> type, deciding what state to leave the input stream in, and deciding 
>> what to do if no number could be found (or if the number was too big 
>> to fit into an int, etc.) This is not^3 simple!
>>
>> C starts with a simple and principled answer, which is that the IO 
>> primitive is getchar() and putchar().  Reading or writing one 
>> character is unquestionably a primitive.  (But also, unless you are 
>> writing `cat`, no one wants to program with getchar and putchar, 
>> because it's too primitive.)
>>
>> One can make a reasonable case for "write a line / read a line" being 
>> sensible primitives.  They are simple enough: no parsing, no deciding 
>> what to throw away, no possible errors other than EOF, it is clear 
>> what state you leave the stream in.  These may not be what the 
>> student wants, but they are primitives a student can deal with 
>> without having to understand parsing and error handling and 
>> statefulness yet.
>>
>>      String s = getALine();
>>      printALine(s);
>>
>> is a program every student can reason about.
>>
>> But, it is true that dealing in strings, while honest and simple, is 
>> not always what the student wants.  But herein lies the strongest 
>> argument for not trying to reinvent Scanner here: the ability to read 
>> numbers makes the complexity of the problem, and hence of the API, 
>> much much bigger.  (Scanner was very well intentioned, and was not 
>> written by children, and yet none of us want to use it.  That's a 
>> sign that a one-size-fits-all magic input processing system is harder 
>> than it looks, and for something that is explicitly aimed at 
>> beginners, is a double warning sign.)
>>
>> I could imagine someone suggesting "why don't you just add 
>> `readLineAsInt`".  But what would happen next?  Well, there would be 
>> a million requests (including from folks like Cay) of "you should add 
>> X", and then the result is a mishmash jumble of an API (that's 
>> already terrible), but worse, it's an onramp that leads to nowhere.  
>> Once the user's needs are slightly more complicated, they are nowhere.
>>
>> Remi has it absolutely right (yes, I really said that) with
>>
>>> The classical program is:
>>>    input -> strings -> objects -> strings -> output
>>
>> We do not do users a favor by blurring the distinction between "input 
>> -> string" and "string -> object", and because the latter is so much 
>> more open-ended than the former, the latter infects the former with 
>> its complexity if we try.
>>
>> Is this simple API the most wonderful, be-all of APIs?  Of course 
>> not.  But it is a sensible set of primitives that users can 
>> understand and *build on* in a transparent way.
>>
>> Some teachers may immediately reach for teaching Integer::parseInt; 
>> that's a reasonable strategy, it exposes students to the questions of 
>> "what happens when preconditions fail", and the two compose just 
>> fine.  But maybe you don't like Integer::parseInt for some reason.  
>> Another way to teach this is to have them write it themselves.  This 
>> will expose them to all sorts of interesting questions (what about 
>> whitespace? what about double negatives?), but of course is also 
>> throwing in the deep end of the pool.  But 
>> SimpleIO::readMeALinePlease is agnostic; it works with both approaches.
>>
>> Could the JDK use some better tools for parsing?  Sure; pattern 
>> matching has a role to play here, a `String::unformat` would be 
>> really cool, and I love parser combinators.  All of this can happen 
>> in the future, and none have the effect of making this API look like 
>> yet another white elephant like Scanner.  Because it focused purely 
>> on the basics.
>>
>>
>> On 2/19/2024 7:25 AM, Remi Forax wrote:
>>> I agree with Brian here,
>>> as a teacher, you have to talk about parsing and formatting, those 
>>> should not be hidden.
>>>
>>> The classical program is:
>>>    input -> strings -> objects -> strings -> output
>>>
>>> Rémi
>>>
>>> ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ 
>>>
>>>
>>>     *From: *"Tagir Valeev" <amaembo at gmail.com>
>>>     *To: *"Cay Horstmann" <cay at horstmann.com>
>>>     *Cc: *"Brian Goetz" <brian.goetz at oracle.com>, "amber-dev" 
>>> <amber-dev at openjdk.org>
>>>     *Sent: *Monday, February 19, 2024 10:09:35 AM
>>>     *Subject: *Re: SimpleIO in JEP draft 8323335
>>>
>>>     I agree that simple methods to get numeric input are essential 
>>> for beginners. They should not be distracted with a complex 
>>> ceremony. Instead, they should be able to learn control flow 
>>> statements and simple algorithms as soon as possible, having a 
>>> simple way to get numbers from the user.
>>>     With best regards,
>>>     Tagir Valeev.
>>>
>>>     On Mon, Feb 19, 2024 at 9:10 AM Cay Horstmann 
>>> <cay at horstmann.com> wrote:
>>>
>>>         Yes, that's what I am saying. If scanners live in vain, 
>>> stick with a subset of the Console methods. Use its readLine. Make 
>>> it so that SimpleIO uses System.console(). And add print and println 
>>> to Console.
>>>
>>>         The JEP talks about being able to start programming without 
>>> having to know about static methods. How does a beginner read a 
>>> number? With Integer.parseInt(readLine(prompt))?
>>>
>>>         What about locales? Is print/println localized? 
>>> Console.printf is. If so, how are beginners from around the world 
>>> supposed to read localized numbers? With 
>>> NumberFormat.getInstance().parse(readLine(prompt))?
>>>
>>>         Adding localized readInt/readDouble to SimpleIO might do the 
>>> trick. Do they consume the trailing newline? (The equivalent Scanner 
>>> methods don't, which is definitely a sharp edge for beginners.)
>>>
>>>         On 18/02/2024 23.08, Brian Goetz wrote:
>>>         > OK, so is this really just that that you are bikeshedding 
>>> the name?  Renaming `input` to `readLine`?
>>>         >
>>>         > This is a perfectly reasonable naming choice, of course, 
>>> but also, not what you suggested the first time around:
>>>         >
>>>         >  > ... "a third API" ...
>>>         >
>>>         >  > ... "there are two feasible directions" ...
>>>         >
>>>         > So what exactly are you suggesting?
>>>         >
>>>         >
>>>         >
>>>         > On 2/18/2024 5:03 PM, Cay Horstmann wrote:
>>>         >> Like I said, either the scanner methods or the console 
>>> methods are fine.
>>>         >>
>>>         >> I am of course aware of the utility/complexity of 
>>> Scanner, and can understand the motivation to have a simpler/feebler 
>>> behavior in SimpleIO. Like the one in Console.
>>>         >>
>>>         >> You don't have to "get a console". A SimpleIO.readLine 
>>> method can just invoke readLine on the system console.
>>>         >>
>>>         >> My objection is to add yet another "input" method into 
>>> the mix. "input" is weak. Does it read a token or the entire line? 
>>> Does it consume the newline? And if it does just what readLine does, 
>>> why another method name? Because "input" is three characters fewer? 
>>> Let's not count characters.
>>>         >>
>>>         >> On 18/02/2024 22.43, Brian Goetz wrote:
>>>         >>> I think you are counting characters and not counting 
>>> concepts.
>>>         >>>
>>>         >>> Scanner has a ton of complexity in it that can easily 
>>> trip up beginners.  The main sin (though there are others) is that 
>>> input and parsing are complected (e.g., nextInt), which only causes 
>>> more problems (e.g., end of line issues.)   Reading from the console 
>>> is clearly a () -> String operation.  The input() method does one 
>>> thing, which is get a line of text.  That's simple.
>>>         >>>
>>>         >>> Integer.parseInt (or, soon, patterns that match against 
>>> string and bind an int) also does one thing: convert a string from 
>>> int.  It may seem verbose to have to do both explicitly, but it 
>>> allows each of these operations to be simple, and it is perfectly 
>>> obvious what is going on. On the other hand, Scanner is a world of 
>>> complexity on its own.
>>>         >>>
>>>         >>> Console::readLine is nice, but first you have to get a 
>>> Console. ("Why can I print something without having to get some 
>>> magic helper object, but I can't do the same for reading?")  What 
>>> we're optimizing for here is conceptual simplicity; the simplest 
>>> possible input method is the inverse of println.  The fact that 
>>> input has to be validated is a fact of life; we can treat validation 
>>> separately from IO (and we should), and it gets simpler when you do.
>>>         >>>
>>>         >>> On 2/18/2024 4:12 PM, Cay Horstmann wrote:
>>>         >>>> I would like to comment on the simplicity of 
>>> https://openjdk.org/jeps/8323335 for beginning students.
>>>         >>>>
>>>         >>>> I am the author of college texts for introductory 
>>> programming. Like other authors, I introduce the Scanner class (and 
>>> not Console) for reading user input. Given that students already 
>>> know about System.out, it is simpler to call
>>>         >>>>
>>>         >>>> System.out.print("How old are you? ");
>>>         >>>> int x = in.nextInt(); // in is a Scanner
>>>         >>>>
>>>         >>>> than
>>>         >>>>
>>>         >>>> int x = Integer.parseInt(console.readLine("How old are 
>>> you? "));
>>>         >>>>
>>>         >>>> or with the JEP draft:
>>>         >>>>
>>>         >>>> int x = Integer.parseInt(input("How old are you? "));
>>>         >>>>
>>>         >>>> Then again, having a prompt string is nice too, so I 
>>> could imagine using the Console API with Integer.parseInt and 
>>> Double.parseDouble, instead of Scanner.nextInt/nextDouble.
>>>         >>>>
>>>         >>>> But why have a third API, i.e. "input"?
>>>         >>>>
>>>         >>>> I think there are two feasible directions. Either 
>>> embrace the Scanner API and next/nextInt/nextDouble/nextLine, or the 
>>> Console API and readLine. Adding "input" into the mix is just 
>>> clutter, and ambiguous clutter at that. At least readLine makes it 
>>> clear that the entire line is consumed.
>>>         >>>>
>>>         >>>> Cheers,
>>>         >>>>
>>>         >>>> Cay
>>>         >>>>
>>>         >>>> --
>>>         >>>>
>>>         >>>> Cay S. Horstmann | 
>>> https://urldefense.com/v3/__http://horstmann.com__;!!ACWV5N9M2RV99hQ!IuXZk_tqIH8rEw1bD3uYb8UcIZF-nnoeFT3UG17pMO5EVXIYVRaAKi7XCq_T02HwnAek1wuV8Wed08w$ 
>>> | mailto:cay at horstmann.com
>>>         >>>
>>>         >>
>>>         >
>>>
>>>         --
>>>         --
>>>
>>>         Cay S. Horstmann | 
>>> https://urldefense.com/v3/__http://horstmann.com__;!!ACWV5N9M2RV99hQ!JDq2P0DR423V62MvLF-CBrjfMSFshyy9lkQdQQPt5aEojp3WbQriYDtG-00NepYgsFay4aXHAQFHA24$ 
>>> <https://urldefense.com/v3/__http://horstmann.com__;!!ACWV5N9M2RV99hQ!IZrLgaQxOHBjUURoC5mWbfsijev257bb4C0DMamUDpoGqS5JMACpaMKsbUNQlWcGds7fifmS9sARC6aKMHEf$> 
>>> | mailto:cay at horstmann.com
>>>
>>>
>>
>

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