RFR: 8299852: Modernize ConcurrentHashMap

[Martin Buchholz]

On Tue, 10 Jan 2023 10:32:34 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

src/java.base/share/classes/java/util/concurrent/ConcurrentHashMap.java line 104:

> 102:  * {@code size}, {@code isEmpty}, and {@code containsValue} are typically
> 103:  * useful only when a map is not undergoing concurrent updates in other threads.
> 104:  * Otherwise, the results of these methods reflect transient states

I agree the added comma here is an improvement.

src/java.base/share/classes/java/util/concurrent/ConcurrentHashMap.java line 357:

> 355:      * sometimes deviate significantly from uniform randomness.  This
> 356:      * includes the case when N > (1<<30), so some keys MUST collide.
> 357:      * Similarly, for dumb or hostile usages in which multiple keys are

"Similarly" should almost always be followed by a comma, but this is an exception.

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