Task for an aspiring JDK contributor

[Ethan McCue]

The problem is that would necessitate a new public class that is *only*
used as a return value. Since it would then come up with auto complete for
people searching for ArrayList, that's non trivial.

Deprecated also isn't the right concept. Mechanically it puts a line
through a method invocation, but this is a more specific sort of
disclaimer. Like a @Unsupported.

There is a whole separate universe of pitches for more standard
annotations, but efforts like that would probably have to start in the
community like jspecify is attempting for nullness annotations.

On Fri, Nov 18, 2022, 12:47 PM Andreas Røsdal <andreas.rosdal at gmail.com>
wrote:

> How about this as a proposed solution to avoid
> UnsupportedOperationException:
> 1. Renamed the internal ArrayList to ArrayWrappingList
> 2. Override add() in ArrayWrappingList and make it deprecated to warn
> people from using it.
>
>
> On Fri, Nov 18, 2022 at 6:23 PM Ethan McCue <ethan at mccue.dev> wrote:
>
>> I think there is potentially actionable feedback in that the exception
>> thrown when users bump into this limitation kinda sucks
>>
>> jshell> Arrays.asList(1, 2, 3).add(4);
>> |  Exception java.lang.UnsupportedOperationException
>> |        at AbstractList.add (AbstractList.java:155)
>> |        at AbstractList.add (AbstractList.java:113)
>> |        at (#8:1)
>>
>> jshell> try { Arrays.asList(1, 2, 3).add(4);} catch (Exception e) {
>> System.out.println(e.getMessage());}
>> null
>>
>> I think there would be value in overriding "add" and other such
>> operations to provide enough context for users to *understand* that
>> * they did an unsupported operation
>> * the list given by `Arrays.asList` was the cause
>>
>> If I had to guess, that's the core of the frustration. The process to get
>> from "not understanding what went wrong" -> "understanding what went wrong"
>> -> "knowing how to fix it" is high.
>>
>> The design problem is how much context can be conveyed in an exception
>> message/stack trace.
>>
>> There is a similar conversation to be had for the collections returned by
>> List.of() and similar.
>>
>> jshell> List.of().add(1)
>> |  Exception java.lang.UnsupportedOperationException
>> |        at ImmutableCollections.uoe (ImmutableCollections.java:142)
>> |        at ImmutableCollections$AbstractImmutableCollection.add
>> (ImmutableCollections.java:147)
>> |        at (#6:1)
>>
>> jshell> try { List.of(1, 2, 3).add(4);} catch (Exception e) {
>> System.out.println(e.getMessage());}
>> null
>>
>> There is a clue in the stack trace here though for List.of() with the
>> "ImmutableCollections" calls. Maybe if we took two moves
>>
>> 1. Renamed the internal ArrayList to something like ArrayWrappingList
>> 2. Overrode add
>>
>> then the stack trace could be enough (or better than the status quo)
>>
>> jshell> Arrays.asList(1, 2, 3).add(4);
>> |  Exception java.lang.UnsupportedOperationException
>> |        at ArrayWrappingList.add (ArrayWrappingList.java:155)
>> |        at ArrayWrappingList.add (ArrayWrappingList.java:113)
>> |        at (#8:1)
>>
>> On Fri, Nov 18, 2022 at 12:14 PM Andreas Røsdal <andreas.rosdal at gmail.com>
>> wrote:
>>
>>> `new ArrayList<>(Arrays.asList(array))`  is quite complex syntax to
>>> convert an array to an java.util.ArrayList,
>>> so a suggestion could be to add a new method to Arrays to convert an
>>> array to a normal java.util.ArrayList which is modifiable.
>>>
>>> Are there any low-hanging-fruit issues in core-libs-dev in
>>> bugs.openjdk.org that you are aware of that
>>> you would like me to help you implement?
>>>
>>> Thanks for considering my request.
>>>
>>> Regards,
>>> Andreas
>>>
>>>
>>>
>>>
>>> On Fri, Nov 18, 2022 at 5:51 PM Daniel Fuchs <daniel.fuchs at oracle.com>
>>> wrote:
>>>
>>>> Hi Andreas,
>>>>
>>>> First of all, congratulations for seeking advice before working on
>>>> a PR. This is exactly how first contributions should start. Thank
>>>> you for that!
>>>>
>>>> Given the area in which you intended to work however, `core-libs-dev`
>>>> might have been a better list than `discuss` to start from.
>>>>
>>>> With regard to the meat of the issue however, and as noted by Ethan,
>>>> Arrays.asList() behaves as intended, and changing that would be a
>>>> major incompatible change, as many users of the API expect the list
>>>> returned by Arrays.asList to be immutable (and depend on it).
>>>> It is not possible nor desirable to change that.
>>>>
>>>> As for your observation, I believe that:
>>>>
>>>>    `new ArrayList<>(Arrays.asList(array))`
>>>>
>>>> will get you what you want.
>>>>
>>>> best regards,
>>>>
>>>> -- daniel
>>>>
>>>> On 18/11/2022 16:29, Andreas Røsdal wrote:
>>>> > Yes, the exception comes when adding objects to the returned list. So
>>>> I
>>>> > would like a convenient way to use Arrays to convert an array to a
>>>> > normal modifiable java.util.ArrayList, instead of this AbstractList.
>>>> >
>>>> >
>>>> > On Fri, Nov 18, 2022 at 5:23 PM Ethan McCue <ethan at mccue.dev
>>>> > <mailto:ethan at mccue.dev>> wrote:
>>>> >
>>>> >     What situation were you encountering the exception? Was it when
>>>> >     trying to add to the returned list?
>>>> >
>>>> >     If so, that's expected. Arrays.asList only wraps an underlying
>>>> >     array, it can't grow it. By that measure List.of() is even more
>>>> >     unintuitive because you can't set anything.
>>>> >
>>>> >     On Fri, Nov 18, 2022, 11:06 AM Andreas Røsdal
>>>> >     <andreas.rosdal at gmail.com <mailto:andreas.rosdal at gmail.com>>
>>>> wrote:
>>>> >
>>>> >         Hello!
>>>> >
>>>> >         I am an aspiring JDK contributor, having used Java in my work
>>>> as
>>>> >         a developer.
>>>> >
>>>> >         I was recently surprised by an Exception thrown when using the
>>>> >         java.util.Arrays.asList() method
>>>> >         so I would like to propose some improvements to this API. In
>>>> >         particular:
>>>> >         - When using java.util.Arrays.asList() then AbstractList is
>>>> >         throwing UnsupportedOperationException which is not
>>>> >         user-friendly or intuitive.
>>>> >         - java.util.Arrays.asList() returning a private class called
>>>> >         ArrayList, which is not the usual java.util.ArrayList, so it's
>>>> >         not user-friendly or intuitive.
>>>> >
>>>> >         Since this would be my first contribution to the JDK, and the
>>>> >         goal is to complete the contribution with accepted pull
>>>> request
>>>> >         and get the Arrays API improved, what would the first step to
>>>> >         making this first improvement to the JDK be?
>>>> >
>>>> >         I would also like to share a link to an open source project
>>>> I've
>>>> >         been working on:
>>>> >         https://github.com/fciv-net/fciv-net
>>>> >         <https://github.com/fciv-net/fciv-net>
>>>> >
>>>> >         Thank you!
>>>> >
>>>> >         Regards,
>>>> >         Andreas R.
>>>> >
>>>>
>>>>
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