Modernize Java

Modernize Java Code

Update the target code to use modern Java features:

• Records instead of mutable POJOs where the type is a value carrier
• Switch expressions with arrow syntax and exhaustiveness checking
• Pattern matching for instanceof and switch
• Local variable type inference (var) where it helps readability
• Virtual threads (Java 21+) for I/O-bound operations — Executors.newVirtualThreadPerTaskExecutor()
• Sealed classes when the type hierarchy is closed
• Text blocks for multiline strings
• Sequenced collections (Java 21+) where ordered access matters
• Collection factory methods (List.of, Map.of, Map.entry)

Constraints

• Don't change behavior — preserve the public API and observable semantics.
• Don't apply var where the inferred type would harm readability (e.g., factory results that could be any of several types).
• If the project's target Java version is below 21, skip the 21+ features and note it in your summary.
• Run the test suite after non-trivial changes; if tests don't exist, surface that as a follow-up rather than as a blocker.