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Long time reader Brent Boyer points out that my point "if you have done all the updating of the HashMap in a single thread or synchronized, then after that it's safe to access it from multiple threads (if they have the view of the map after updating has finished)" from September's newsletter is specific to the existing HashMap implementation; another (future) implementation could perfectly reasonably mutate the map on reads, with Brent giving a desired example of a self-adapting HashMap that changes its internal structure to optimize the read pattern it is being used with, as it monitors those reads.

And of course that's quite true. I wasn't saying that you SHOULD do that with HashMap. If you have a concurrent use for a hashed based map you should definitely use ConcurrentHashMap, and indeed I recommend (as I did last August) that you actually use ConcurrentHashMap as your default map implementation so that maintenance changes are handled correctly.

My point in September's newsletter was about maintenance and could be misconstrued so let me be more accurate:

Now on to our usual links to articles, tools, news, talks, blogs. And if you need the tips from this month's articles and talks, as ever they are extracted into this month's tips page.

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Last Updated: 2023-08-28
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