RFR: 8358526: Clarify behavior of java.awt.HeadlessException constructed with no-args

[Alexey Ivanov]

On Fri, 20 Jun 2025 22:22:53 GMT, Harshitha Onkar <honkar at openjdk.org> wrote:

>> Clarify the behaviour of new HeadlessException().getMessage()
>> The spec. is updated to be clear that empty means null, not an empty string.
>
> test/jdk/java/awt/Headless/HeadlessExceptionTest.java line 37:
> 
>> 35:     public static void main (String[] args) {
>> 36:         String nullmsg = new HeadlessException().getMessage();
>> 37:         String emptymsg = new HeadlessException("").getMessage();
> 
> @prrace I was thinking of a case which would actually throw HeadlessException when run with `Djava.awt.headless=true`  such as creating a frame or robot but the exception msg can be null or default message from GraphicsEnvironment so making it difficult to validate on different platforms. The current test works well to validate both empty and null message.

Since this test is run on *headless* hosts, the default headless message will always be present on Linux, therefore `nullmsg` will not be `null`.

If the test is run on headful hosts, the message should be `null` and empty string correspondingly.

@honkar-jdk Do you suggest a test needs expanding to cover both cases where the default headless message is present or not?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25881#discussion_r2163891474