RFR: 8348648: Unnecessary Hashtable usage in javax.swing.text.html.CSS.LengthUnit

[Sergey Bylokhov]

On Mon, 20 Jan 2025 13:07:19 GMT, Andrey Turbanov <aturbanov at openjdk.org> wrote:

> Two `Hashtable`'s in `javax.swing.text.html.CSS.LengthUnit` class are modified only within `<clinit>` block:
> 1. lengthMapping
> 2. w3cLengthMapping
> 
> We can replace them with immutable maps to avoid Hashtable synchronization overhead.

Marked as reviewed by serb (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/23198#pullrequestreview-2579689084