RFR: 8343418: Use HashMap instead of Hashtable for CSS.htmlAttrToCssAttrMap

[ExE Boss]

On Wed, 30 Oct 2024 12:02:14 GMT, Andrey Turbanov <aturbanov at openjdk.org> wrote:

> If a thread-safe implementation is not needed, it is recommended to use HashMap instead of legacy synchronized Hashtable. 
> Map `CSS.htmlAttrToCssAttrMap` is modified only within static initialization block and then only `get` method is called.
> 
> The only subtle difference is that Hashtable doesn't allow `null` keys and throws NPE from `get` method.
> I've checked all possible keys which are passed to `htmlAttrToCssAttrMap.get`.
> Currently 3 different execution paths are possible:
> 
> **1,2**
> When `HTML.Attribute.BORDER` is passed as a key. It's definitely non-null.
> 
> javax.swing.text.html.CSS#translateHTMLToCSS
>   translateAttribute(HTML.Attribute.BORDER, "1", cssAttrSet);
>     CSS.Attribute[] cssAttrList = getCssAttribute(key);
> 
> 
> javax.swing.text.html.CSS#translateAttributes
>    translateAttribute(HTML.Attribute.BORDER, Integer.toString(borderWidth), cssAttrSet);
>      CSS.Attribute[] cssAttrList = getCssAttribute(key);`
> 
> 
> **3**
> When non-null `key` is passed as a key.
> 
> javax.swing.text.html.CSS#translateAttributes
> 
>     if (name instanceof HTML.Attribute) { // from this `instanceof` we know that it's non-null
>          HTML.Attribute key = (HTML.Attribute)name;
> 
>       translateAttribute(key, (String) htmlAttrSet.getAttribute(key), cssAttrSet);
>         CSS.Attribute[] cssAttrList = getCssAttribute(key);
> 
> 
> ![idea_analyze_dataflow_to_here](https://github.com/user-attachments/assets/48ace4de-6d0a-468e-bb14-b579a193254b)
> 
> 
> I've used HashMap.newHashMap method instead of constructor to avoid resizing of internal HashMap array.

If there are no initialisation circularities between [`javax.swing.text.html.CSS`] and [`javax.swing.text.html.HTML`], then it might be possible to use [`Map​.of(…)`] instead, given that these maps aren’t written to after startup.

[`javax.swing.text.html.CSS`]: https://docs.oracle.com/en/java/javase/23/docs/api/java.desktop/javax/swing/text/html/CSS.html
[`javax.swing.text.html.HTML`]: https://docs.oracle.com/en/java/javase/23/docs/api/java.desktop/javax/swing/text/html/HTML.html
[`Map​.of(…)`]: https://docs.oracle.com/en/java/javase/23/docs/api/java.base/java/util/Map.html#ofEntries(java.util.Map.Entry...)

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PR Comment: https://git.openjdk.org/jdk/pull/21785#issuecomment-2451961348