Instruction file imported from PhuongL1/PizzaTime (.github/instructions/java.instructions.md). Copyright stays with the author.

Java — Coding Conventions

Style

• Indentation: 4 spaces
• Naming: camelCase (methods/fields), PascalCase (classes/interfaces), UPPER_SNAKE_CASE (constants)
• Max line length: 120
• Braces: K&R style (opening brace on same line)
• Trailing commas: no

Patterns

• Prefer composition over inheritance
• Use interfaces for abstraction — program to interface, not implementation
• Use Optional<T> for nullable returns — never return null from public methods
• Use final on local variables and parameters when practical
• Avoid raw types — always parameterize generics
• Use Objects.requireNonNull() at method entry for early validation

File structure

• One public class per file
• Order: static fields → instance fields → constructors → public methods → private methods
• Group related methods together

Testing

• Naming: shouldDoX_whenY() or givenX_whenY_thenZ()
• Use JUnit 5 (@Test, @BeforeEach, @Nested)
• Mocking: Mockito (@Mock, @InjectMocks, when().thenReturn())
• Assertions: AssertJ preferred (assertThat(x).isEqualTo(y))

Notes

• Java version: 17+ — use records, sealed classes, pattern matching where appropriate
• Use record for immutable DTOs (instead of POJO with getters/setters)
• Use sealed interface for closed type hierarchies (Java 17+)
• Use text blocks ("""...""") for multi-line strings
• Avoid checked exceptions for business logic — use unchecked + global handler