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

[Harshitha Onkar]

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.

@turbanoff Based on your explanation, it sounds reasonable to convert CSS.htmlAttrToCssAttrMap from Hashtable to HashMap since synchronization may not be required.

There are few more Hashtables - `styleConstantToCssMap, htmlValueToCssValueMap, cssValueToInternalValueMap`. Do we consider converting them as well - either to HashMap or ConcurrentHashMap (if thread-safe synchronization is required)?

LGTM, I would like an additional reviewer to look at the changes.

@aivanov-jdk You may want to take a look at this PR since you recently worked on few issues related to CSS.java [JDK-8326734](https://bugs.openjdk.org/browse/JDK-8326734), [JDK-8335967](https://bugs.openjdk.org/browse/JDK-8335967)

-------------

PR Review: https://git.openjdk.org/jdk/pull/21785#pullrequestreview-2409032205
Marked as reviewed by honkar (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/21785#pullrequestreview-2409051775
PR Comment: https://git.openjdk.org/jdk/pull/21785#issuecomment-2450801134