RFR: 8186958: Need method to create pre-sized HashMap [v5]

[Roger Riggs]

On Thu, 24 Mar 2022 12:10:28 GMT, XenoAmess <duke at openjdk.java.net> wrote:

>> 8186958: Need method to create pre-sized HashMap
>
> XenoAmess has updated the pull request incrementally with one additional commit since the last revision:
> 
>   delete a space.

src/java.base/share/classes/java/util/HashMap.java line 2549:

> 2547: 
> 2548:     /**
> 2549:      * Calculate initial capacity for HashMap based classes, from expected size.

This method should say it is using a default load factor  (0.75).
I'm not sure how often anyone creates a map with a non-default load factor
but that might suggest a more general API pattern either in the supporting calculation
or the public factories.

src/java.base/share/classes/java/util/HashMap.java line 2556:

> 2554:      */
> 2555:     static int calculateHashMapCapacity(int expectedSize) {
> 2556:         if (expectedSize >= 1610612736) {

It would be clearer with a comment on the constant or use the expression (the compiler will evaluate it).
`Integer.MAX_VALUE / 4 * 3`.

There also might be a valid point to make about a fail-fast exception if the requested capacity cannot be achieved.   If defaulted to MAX_VALUE, the application would start populating the map and then at some later point get an exception when it cannot be resized to accommodate the n+1'th item.

src/java.base/share/classes/java/util/HashMap.java line 2565:

> 2563:      * Creates a new, empty HashMap with an initial table size
> 2564:      * accommodating the specified number of elements without the need
> 2565:      * to dynamically resize.

The default load factor should be mentioned.

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PR: https://git.openjdk.java.net/jdk/pull/7928