<html><body><div style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000"><div><br></div><div><br></div><hr id="zwchr" data-marker="__DIVIDER__"><div data-marker="__HEADERS__"><blockquote style="border-left:2px solid #1010FF;margin-left:5px;padding-left:5px;color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;"><b>From: </b>"Brian Goetz" <brian.goetz@oracle.com><br><b>To: </b>"david Grajales" <david.1993grajales@gmail.com>, "amber-dev" <amber-dev@openjdk.org><br><b>Sent: </b>Saturday, July 26, 2025 11:48:49 PM<br><b>Subject: </b>Re: Thoughts on Array Initialization in JavaONE 2025<br></blockquote></div><div data-marker="__QUOTED_TEXT__"><blockquote style="border-left:2px solid #1010FF;margin-left:5px;padding-left:5px;color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;">All of the points you raise that "arrays are not the abstraction you
are looking for" are absolutely true -- and well understood. The
goal of improving array creation is not to help arrays win market
share away from collections.<br>
<br>
But there is a reason that the language has arrays, and that reason
hasn't gone away. Arrays are the bottom brick on which the tower of
better data structures are built. You can't have ArrayList or
HashMap without arrays. Arrays are part of the language for a
reason. As we improve the language, sometimes arrays have to
improve with it. (For example, if you have a
non-implicitly-constructible value class NVA (one who has no valid
default value), and someone wants to create an array of NVA![n],
allowing the existing "zero the memory" array creation expression to
create it would undermine the integrity of the runtime by exposing
objects that are not in a valid state as determined by their
constructor. So we can't allow that, which means we have to provide
something else.)<br>
<br>
If we hadn't found the need to improve other aspects of
initialization, we probably wouldn't have bothered to improve array
initialization. But because we are improving initialization more
broadly, we have to do the whole job. Not being able to create
interesting arrays linguistically would forever look like a weird
omission. <br>
<br>
Your suggestion -- "why not just" not improve array creation
linguistically, and shunt any sort of exotic array creation to a
privileged API -- leaves the user with little explanation for why
the tower stands up. The bottom brick is not there, instead
replaced by some sort of magic that seems to hold up the brick above
it. While we expect relatively few programmers to program with
arrays (ideally, just the guy who maintains ArrayList and HashMap,
and the like), we should provide linguistic mechanisms for properly
using core linguistic building blocks. <br>
<br>
I can imagine three implicit lines of thought for why you think such
a low-level mechanism should be performed by a privileged library
rather than a language feature: <br>
<br>
- The easier we make it to use, the more people will use it, and
you would like fewer people to use it (as would we.) A
scary-looking library will scare away more people than a
pretty-looking language feature.<br>
- Language features are expensive, more expensive than libraries,
so by shunting this to a library, we preserve resources to focus on
more important things. <br>
- Array initialization appears to be competing for resources with
features like collection literals, and you'd rather have the latter,
so suggesting that we skip the former seems like it would bring the
latter more quickly. <br>
<br>
These are appealing-sounding arguments, but they don't point to
either usability wins or project-management wins. Arrays are the
right tool for some jobs. Collections are the right tool for others
(most others.) But the way to encourage people to use the right
tool is not to make the other tools harder to use. (We too would
like to have linguistic support for creating sets, lists, maps, etc,
but that feature is not competing with arrays, its waiting for
something else.) Nor is the cost of a privileged array-construction
API significantly cheaper than a language feature. </blockquote><div><br></div><div>I always flip-flop between thinking that arrays are redeemable and losing all hope about them :)</div><div><br data-mce-bogus="1"></div><div>I think that the solution to our problem is to use value classes, after all, a value class allows abstraction without the runtime cost, right, so why not eating our own dog food ?</div><div><br data-mce-bogus="1"></div><div>Why not using array wrapped into a value class that implements the List interface ?</div><div><br data-mce-bogus="1"></div><div>By example, here is a List that allows only to access to an element of the List only if it has been initialized first (using a watermark),</div><div><br data-mce-bogus="1"></div><div>value class WatermarkedList<E> implements List<E> {</div><div> E[] array;</div><div> int watermark;</div><div> </div><div> // private constructor + static method</div><div><br data-mce-bogus="1"></div><div> WatermarkedList<E> append(E element) {</div><div> array[watermark] = element;</div><div> return new WatermarkedList<>(array, watermark + 1);</div><div> }</div><div><br data-mce-bogus="1"></div><div> E get(int index) {</div><div> Objects.checkIndex(index, watermark);</div><div> return array[index];</div><div> }</div><div><br data-mce-bogus="1"></div><div> int size() { return watermark; }</div><div><br data-mce-bogus="1"></div><div> WatermarkedList<E> copyOf(int newCapacity) { ... }</div><div><br data-mce-bogus="1"></div><div> ...</div><div>}</div><div><br data-mce-bogus="1"></div><div>Here the array can be initialized with zeroes (using a "JDK restricted" method) and a WatermarkedList is still safe to be used with element that are NVA.</div><div><br data-mce-bogus="1"></div><div>I think the JDK can define few of those lightweight Lists that can be used as primitive by anyone wanting to implement more complex data structures (ArrayList, HashMap, etc).</div><div><br data-mce-bogus="1"></div><blockquote style="border-left:2px solid #1010FF;margin-left:5px;padding-left:5px;color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;"><br>
<br>
Cheers,<br>
-Brian<br>
<br>
<br>
</blockquote><div><br></div><div>regards,</div><div>Rémi</div><div><br data-mce-bogus="1"></div><blockquote style="border-left:2px solid #1010FF;margin-left:5px;padding-left:5px;color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;"><br>
<br>
<br>
<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 7/26/2025 5:03 PM, david Grajales
wrote:<br>
</div>
<blockquote cite="mid:CADFQZ74gJ0C9FTrSGbMBtrECBVevXQrzFwxJ5KFQBaBQ2Sep+g@mail.gmail.com">
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<p>Dear Amber developers,</p>
<p>I recently watched the JavaONE 2025 session titled <em>“A
New Model for Java Object Initialization”</em> and
was particularly intrigued by the proposed
improvements to array initialization.</p>
<p><a href="https://www.youtube.com/watch?v=XtvR4kqK8lo" target="_blank" class="moz-txt-link-freetext">https://www.youtube.com/watch?v=XtvR4kqK8lo</a><br data-mce-bogus="1"></p>
<p><br>
</p>
<p>I strongly agree that Java needs better mechanisms
for initializing data structures in a concise,
expressive, and stricter manner—similar in spirit to
Python’s list comprehensions and aligned with Strict
initialization, required for Valhalla. Such constructs
can help avoid subtle bugs and the presence of
unintended <code>null</code> values. However, I remain
skeptical about the decision to focus this new model
exclusively around arrays.</p>
<p>As has been discussed over the past few months,
arrays are not ideal as a default abstraction,
especially for students or in enterprise applications.
Arrays are a low-level construct with several
limitations:</p>
<ul>
<li>
<p>They do not integrate well with generics.</p>
</li>
<li>
<p>They are of fixed size.</p>
</li>
<li>
<p>They lack methods and flexibility.</p>
</li>
<li>
<p>They are syntactically and semantically
inconsistent with the rest of the Java Collections
Framework.</p>
</li>
</ul>
<p>In many ways, arrays are a legacy feature inherited
from C/C++—much like the original <code>switch</code> statement—that
carry forward certain limitations that Java has
otherwise worked hard to overcome.</p>
<p>Given these issues, Why not just create an small API
that facilitates the creation of the most used data
structures with strict initialization? </p>
<p>For example:</p>
<p><br>
</p>
<p>void main(){</p>
<p><br>
</p>
<p> // toArray</p>
<p> var array =
StrictCollections.toArray(String.class, 5, i ->
"Item-" + i);</p>
<p> IO.println("Array: " + Arrays.toString(array));</p>
<p><br>
</p>
<p> // toList</p>
<p> var list = StrictCollections.toList(5, i ->
"List-" + i);</p>
<p> IO.println("List: " + list);</p>
<p><br>
</p>
<p> // toSet</p>
<p> var set = StrictCollections.toSet(5, i ->
"Set-" + (i % 3));</p>
<p> IO.println("Set: " + set);</p>
<p><br>
</p>
<p><br>
</p>
<p> var map = StrictCollections.toMap(</p>
<p> 5,</p>
<p> i -> "Key-" + i,</p>
<p> i -> i * 100</p>
<p> );</p>
<p> IO.println("Map: " + map);</p>
<p><br>
</p>
<p> </p>
<p>}</p>
<p><br>
</p>
<p><br>
</p>
<p>public static class StrictCollections {</p>
<p><br>
</p>
<p> public static <T> T[]
toArray(Class<T> clazz, int size,
IntFunction<T> function) {</p>
<p> @SuppressWarnings("unchecked")</p>
<p> T[] array = (T[]) Array.newInstance(clazz,
size); // This could be a frozen array once these are
ready</p>
<p> for (int i = 0; i < size; i++) {</p>
<p> array[i] = function.apply(i);</p>
<p> }</p>
<p> return array;</p>
<p> }</p>
<p><br>
</p>
<p> public static <T> ArrayList<T>
toList(int size, IntFunction<T> function) {</p>
<p> var list = new ArrayList<T>(size);</p>
<p> for (int i = 0; i < size; i++) {</p>
<p> list.add(function.apply(i));</p>
<p> }</p>
<p> return list;</p>
<p> }</p>
<p><br>
</p>
<p> public static <T> HashSet<T>
toSet(int size, IntFunction<T> function) {</p>
<p> List<T> list = new
ArrayList<>(size);</p>
<p> for (int i = 0; i < size; i++) {</p>
<p> list.add(function.apply(i));</p>
<p> }</p>
<p> return new HashSet<>(list);</p>
<p> }</p>
<p><br>
</p>
<p> public static <K, V> HashMap<K, V>
toMap(int size, IntFunction<K> kFunction,
IntFunction<V> vFunction) {</p>
<p> HashMap<K, V> map = new
HashMap<>(size);</p>
<p> for (int i = 0; i < size; i++) {</p>
<p> map.put(kFunction.apply(i),
vFunction.apply(i));</p>
<p> }</p>
<p> return map;</p>
<p> }</p>
<p>}</p>
<p>While this is admittedly a rough sketch developed in
just a few minutes, I believe a similar—much more
thoroughly designed—approach could provide much
greater flexibility with far less complexity than
introducing a dedicated array-specific feature. It
would also extend naturally to a broader range of use
cases --Such as being able to be combined with the
Stream API in a much more ergonomic way--.
Furthermore, as value classes and parametric JVM start
to make it into the language and the JVM, the
advantages of arrays and primitive types will diminish
further. In that context, arrays will become even less
compelling in the future.</p>
<p>If Java is to introduce a safe, expressive, and
idiomatic strict initialization literal for data
structures, I would argue it should primarily support <code>List</code>, <code>Set</code>,
and <code>Map</code>—especially <code>Map</code>,
which remains one of the least ergonomic structures to
initialize in the language today, particularly when
compared to alternatives in Dart, Python, or even
JavaScript objects. Data structures that are much more
used.</p>
<p><br>
</p>
<p>Thank you so much for all your work and always yours</p>
<p><br>
</p>
</div>
</div>
</div>
</div>
</div>
</blockquote>
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