Use Collections#isEmpty or String#isEmpty

[iddeepak]

Summary
This PR improves readability and consistency across the codebase by replacing manual size/length checks with more idiomatic methods:

Replaces collection.size() == 0 or collection.size() != 0 with collection.isEmpty() / !collection.isEmpty()

Replaces string.length() == 0 with string.isEmpty()

Motivation
These changes align with modern Java best practices:

isEmpty() is more expressive and self-documenting than comparing .size() or .length() to 0.

This is similar to the MNG-8060 change made in Apache Maven and #10945, which improved code clarity.

Please check :
[Experimental] Add rewrite support for errorprone.refasterrules.StringRulesRecipes
Convert value.trim().length() < 1 to value.isBlank() < 1
https://error-prone.picnic.tech/refasterrules/StringRules

These patterns are common and can be enforced or auto-corrected via CI using static analysis and refactoring tools.

[Pankraz76]

well done, like always!

If not done by some plugin this is kind of waste as it will occure any time again.

If spring really want to solve this issue, by having solution like in check:

• PoC: Add rewrite support for errorprone.refasterrules diffplug/spotless#2576

Kindly let me know @bclozel

[iddeepak]

This is best if rewrite not accepted can we still add a regex in checkstyle to fail the build. Your thoughts @Pankraz76

[Pankraz76]

nice idea, yes give it a try in dedicated pr.

[mdeinum]

IIRC the checks collection.size() == 0 and collection.size() > 0 are deliberate in there. Although it is tempting to use collection.isEmpty() and !collection.isEmpty() they are actually hard to distinguish from one another. The ! is quite easily missed or added by accident, hence usage of .size() instead for readability and to reduce mistakes.

If you want to replace them you could introduce an isNotEmpty method (next to the isEmpty) on the CollectionUtils class and delegate to that. The same could apply for the String checks.

[bclozel]

All classes under the asm.* and cglib.* packages are repackaged classes from the original projects. We track the original projects, update and maintain local patches. Changing the code in this namespace for stylistic reasons is just likely to make our maintenance process harder and error-prone. Readability is not really an issue here, because we only maintain the patches, not the rest of the code. In my opinion those are the only good instances of changes where we have .size() == 0 and .length() == 0. I would suggest sending PRs to the original projects here if you believe this improves readability and maintenance.

As for all the other instances, we're really turning something.size() > 0 into !something.isEmpty(), which I don't think improves readability.

As a result, I'm declining this PR because I don't think there are other cases than the two types listed above.
Thanks!

[iddeepak]

Thank you for detailed feedback, @bclozel