RFR: 8347334: JimageDiffGenerator code clean-ups

[Henry Jen]

On Thu, 9 Jan 2025 17:32:39 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

> During code review of [JDK-8346239](https://bugs.openjdk.org/browse/JDK-8346239) a few comments were made after the PR integrated. This follow-up patch cleans this up and adds a unit test for the `JimageDiffGenerator` class.
> 
> Testing:
> - [ ] GHA
> - [x] tools/jlink tests (including the new one).
> 
> Thoughts?

src/jdk.jlink/share/classes/jdk/tools/jlink/internal/runtimelink/JimageDiffGenerator.java line 133:

> 131:             while ((bytesRead1 = is1.readNBytes(buf1, 0, buf1.length)) != 0) {
> 132:                 bytesRead2 = is2.readNBytes(buf2, 0, buf2.length);
> 133:                 if (bytesRead2 == 0) {

This is redundant to next statement. However, we do need to read and test byteRead2 is also 0 after byteRead1 is 0 and exit the loop.

test/jdk/tools/jlink/runtimeImage/JimageDiffGeneratorTest.java line 1:

> 1: /*

Looks good to me. Nitpick: Most test cases use a common base image can be defined once?

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PR Review Comment: https://git.openjdk.org/jdk/pull/23014#discussion_r1909225813
PR Review Comment: https://git.openjdk.org/jdk/pull/23014#discussion_r1909242794