RFR: 8299852: Modernize ConcurrentHashMap [v2]

[Attila Szegedi]

On Thu, 12 Jan 2023 09:28:46 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> `java.util.concurrent.ConcurrentHashMap` is relatively old and has not been updated to reflect the current state of Java and can be modernized: 
>> 
>> * Add `@Serial` annotations 
>> * Seal classes and restrict subclassing for internal classes 
>> * Use pattern matching for instance 
>> * Remove redundant modifiers (such as some final declarations) 
>> * Use Objects.requireNonNull for invariant checking 
>> * Use diamond operators instead of explicit types 
>> * Simplify expressions using Math::max
>
> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add @Override annotations

src/java.base/share/classes/java/util/concurrent/ConcurrentHashMap.java line 995:

> 993:         Node<K,V>[] t;
> 994:         if ((t = table) != null) {
> 995:             Traverser<K,V> it = new Traverser<>(t, t.length, 0, t.length);

Using diamond is one way to modernize this code, using `var` would be another, even more concise way. Consider: 
Suggestion:

            var it = new Traverser<K, V>(t, t.length, 0, t.length);

I don't support blindly using `var` everywhere, but I believe when the RHS of the assignment spells out the type that's exactly the kind of usage envisioned for it.

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PR: https://git.openjdk.org/jdk/pull/11924