RFR: 8281631: HashMap copy constructor and putAll can over-allocate table [v14]

[XenoAmess]

On Thu, 17 Feb 2022 05:45:54 GMT, Stuart Marks <smarks at openjdk.org> wrote:

> It's not clear to me that test is actually testing anything useful; it's just testing the same computation a couple different ways.

Well if I don't change it, then the test will fail.

> Do the changes to Class.java and the enum optimal capacity test need to be part of this PR? They seem unrelated. 

But on the other hands, as they are not relative to this issue, if you think that test (`test/jdk/java/lang/Enum/ConstantDirectoryOptimalCapacity.java`)is useless and want to delete it, it shall happen elsewhere, but not in this pr.
According to minimal change, I just make it can pass, but have no interest in shutting it down / heavily modify it.

> 1. It should probably be a TestNG test. This will allow you to use a DataProvider and also use TestNG assertions.

good. I learned something about jtreg today and find it can invoke Junit 5.

I would like to migrate this test to Junit 5, it is more familiar to me than TestNG.

> 2. There are 12 test cases here, which seems amenable to using a DataProvider. You could try to make a little "combo" test that combines the three classes with the four ways of creating them, but it might be difficult to do that without using reflection. It might be easier to write a table with 12 cases, even if there is a bit of repetition.
> 3. Instead of writing reflective code to create the maps, it's probably easier to use suppliers that create the maps into the desired state. Each of the 12 test cases should have a lambda that does the creation. The test method then invokes the supplier and makes its assertions over the resulting map instance.
> 4. The `fill12` method can be used in an expression if it returns its argument.
> 5. Create a map with 12 entries as part of the test setup, and then just use it as the copy constructor argument.

OK, would have a try.

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PR: https://git.openjdk.java.net/jdk/pull/7431