Java Language Patterns

Priority: P0 (CRITICAL)

Modern Java (21+) standards for concise, immutable, and expressive code.

Implementation Guidelines

• Records: Use record for immutable DTOs/Value Objects. Records auto-generate equals, hashCode, toString. Avoid Lombok @Data on Pojos.
• Local Variables: Use

  var

  for inferred types. Explicitly type interface variables.
• Switch: Use Switch Expressions (->) and Pattern Matching over complex if/else chains.
• Text Blocks: Use

  """ (Text Blocks)

  for JSON, SQL, or multi-line strings.
• Pattern Matching: Use

  instanceof

  with pattern binding:

  if (obj instanceof String s)

  .
• Sealed Classes: Use sealed interface/class with permits clause for domain-driven restricted hierarchies. Switch expressions are then exhaustive switch (compiler-verified).
• Collections: Use

  List.of()

  ,

  Map.of()

  , and

  Set.of()

  for immutable collections.
• Streams: Use

  stream()

  pipelines for functional transformations. Use

  .toList()

  (Java 16+).
• Optional: Utilize

  Optional<T>

  for return types. Use

  .ifPresentOrElse()

  or

  .orElseThrow()

  .
• Virtual Threads: Favor

  Executors.newVirtualThreadPerTaskExecutor()

  for I/O-heavy workloads.

Anti-Patterns

• No Nulls: Return Optional or empty collections; avoid null parameters.
• No Raw Types: Always use generics; never use raw List or Map.
• No Old Switch: Use switch expressions (->); avoid fall-through.
• No Manual get/set: Use Records or value objects instead.
• No synchronized blocks: Use java.util.concurrent or Virtual Threads instead.

References

• Records, Pattern Matching & Virtual Threads