refactor: improve code quality by enforcing final on utility classes and extracting complex methods

[nafisa1602]

What issues were addressed

• Class With Only Private Constructors Should Be Final: Made NumberLimits,
  PreJava9DateFormatProvider, ReflectionAccessFilterHelper, TroubleshootingGuide,
  FormattingStyle, ISO8601Utils, and SqlTimestampTypeAdapter final
• Loose Coupling: Changed ArrayDeque to Deque interface in GsonBuilder
• Cognitive Complexity/ Cyclomatic Complexity: Extracted excludeField() checks
  into private named methods in Excluder

Why the changes improve the system

• final on utility classes prevents unintended subclassing and communicates
  design intent clearly to future maintainers
• Interface types over implementation types improves flexibility
• Extracted methods reduce cognitive complexity of excludeField() from 18 to
  near 0 and make each exclusion rule independently readable and testable

Refactoring approach

Extract Method and programming to interfaces patterns, guided by PMD static analysis.

Functionality unchanged

All 4603 existing tests pass with 0 failures after every change.

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[Marcono1234]

Thanks!

The changes look mostly good to me. I have added two comments, feel free to consider them only as suggestions.
The direct project members might have additional comments.

[Marcono1234]

Maybe it would be worth discussing whether this trimToSize() here is really needed or is premature optimization, but since the purpose of your PR is only to use "interface types over implementation types", I think this functionality change should be reverted for this PR. That is, please change the local variable back to ArrayList and add back the trimToSize() call.

Generally "interface types over implementation types" is a good principle, but for internal code it is bit less relevant, even more so if this only applies to a local variable and the specific implementation type is needed because the needed functionality does not exist for the interface type (as it is the case here).

[Marcono1234]

Can you please revert this? It seems to be specific to your development setup and is probably not useful for most other contributors.

[nafisa1602]

Thanks for the review! I've reverted the createFactories change back to ArrayList with trimToSize() and removed the maven tarball entry from .gitignore. Let me know if anything else needs adjusting.

…

On Mon, Jun 29, 2026 at 6:21 PM Marcono1234 ***@***.***> wrote: ***@***.**** commented on this pull request. Thanks! The changes look mostly good to me. I have added two comments, feel free to consider them only as suggestions. The direct project members might have additional comments. ------------------------------ In gson/src/main/java/com/google/gson/GsonBuilder.java <#3049 (comment)>: > @@ -997,7 +998,6 @@ List<TypeAdapterFactory> createFactories( jsonAdapterFactory, newImmutableList(reflectionFilters))); - factories.trimToSize(); Maybe it would be worth discussing whether this trimToSize() here is really needed or is premature optimization, but since the purpose of your PR is only to use "interface types over implementation types", I think this functionality change should be reverted for this PR. That is, please change the local variable back to ArrayList and add back the trimToSize() call. Generally "interface types over implementation types" is a good principle, but for internal code it is bit less relevant, even more so if this only applies to a local variable and the specific implementation type is needed because the needed functionality does not exist for the interface type (as it is the case here). ------------------------------ In .gitignore <#3049 (comment)>: > @@ -18,3 +18,4 @@ local.properties build .DS_Store +apache-maven-3.9.6-bin.tar.gz Can you please revert this? It seems to be specific to your development setup and is probably not useful for most other contributors. — Reply to this email directly, view it on GitHub <#3049?email_source=notifications&email_token=BOI67X7A3TIDFOLSXU35XYD5CJNM7A5CNFSNUABKM5UWIORPF5TWS5BNNB2WEL2QOVWGYUTFOF2WK43UKJSXM2LFO4XTINJZGE3TENRUGUYKM4TFMFZW63VGMF2XI2DPOKSWK5TFNZ2KYZTPN52GK4S7MNWGSY3L#pullrequestreview-4591726450>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/BOI67X6GUHGPJL3JYTSCN3D5CJNM7AVCNFSNUABEKJSXA33TNF2G64TZHMZTENJTHA4DOMJ3JFZXG5LFHM2DONRUG44DONZVGOQXMAQ> . Triage notifications, keep track of coding agent tasks and review pull requests on the go with GitHub Mobile for iOS <https://github.com/notifications/mobile/ios/BOI67X7OH3F5L6JPPKFWBDT5CJNM7A5CNFSNUABKM5UWIORPF5TWS5BNNB2WEL2QOVWGYUTFOF2WK43UKJSXM2LFO4XTINJZGE3TENRUGUYKM4TFMFZW63VGMF2XI2DPOKSWK5TFNZ2KUZTPN52GK4S7NFXXG> and Android <https://github.com/notifications/mobile/android/BOI67X2KMEYS3UPDNH5AOB35CJNM7A5CNFSNUABKM5UWIORPF5TWS5BNNB2WEL2QOVWGYUTFOF2WK43UKJSXM2LFO4XTINJZGE3TENRUGUYKM4TFMFZW63VGMF2XI2DPOKSWK5TFNZ2K4ZTPN52GK4S7MFXGI4TPNFSA>. Download it today! You are receiving this because you authored the thread.Message ID: ***@***.***>