autojanet/skills/understand/languages/java.md

Java Language Prompt Snippet

Key Concepts

• Generics (with Erasure): Parameterized types erased at runtime; compile-time safety only
• Annotations: Metadata markers (@Override, @Autowired) processed at compile or runtime
• Interfaces and Abstract Classes: Contracts with default methods (Java 8+) and partial implementations
• Streams API: Functional-style pipeline operations on collections (filter, map, reduce)
• Lambdas: Concise anonymous function syntax for functional interfaces
• Sealed Classes: Restricted class hierarchies with explicit permitted subclasses (Java 17+)
• Records: Immutable data carriers with auto-generated accessors, equals, hashCode (Java 16+)
• Dependency Injection: IoC pattern central to Spring; constructor, field, or method injection
• Checked vs Unchecked Exceptions: Checked must be declared or caught; unchecked extend RuntimeException
• Optional: Container for nullable values encouraging explicit handling over null checks

Import Patterns

• import package.Class — import a specific class
• import package.* — wildcard import of all classes in a package
• import static package.Class.method — static import for direct method/constant access

File Patterns

• src/main/java/ — source root following Maven/Gradle standard layout
• src/test/java/ — test source root with matching package structure
• pom.xml — Maven project configuration and dependency management
• build.gradle — Gradle build script (Groovy or Kotlin DSL)
• Application.java — Spring Boot entry point with @SpringBootApplication

Common Frameworks

• Spring Boot — Opinionated framework for production-ready Spring applications
• Jakarta EE — Enterprise Java standards (formerly Java EE) for server-side development
• Quarkus — Cloud-native framework optimized for GraalVM and containers
• Micronaut — Compile-time DI framework for microservices and serverless
• Hibernate — ORM framework implementing JPA specification

Example Language Notes

Uses @Autowired annotation for constructor injection, following Spring IoC container pattern. Constructor injection is preferred over field injection because it makes dependencies explicit and enables immutability.

The Maven standard directory layout (src/main/java, src/test/java) is a strong convention — most build tools and IDEs expect this structure by default.