java-solid— agent skill

Review the provided Java code for SOLID principles violations. For each principle, check for violations and suggest targeted improvements. Tailor suggestions to the detected Java version.

S — Single Responsibility Principle

A class should have one reason to change.

Violations to flag:

• Classes named *Manager, *Helper, *Utils with more than 3 unrelated methods
• Service classes that also contain validation logic, email sending, AND database calls
• Classes with more than ~200 lines (often a signal of multiple responsibilities)
• Methods that do multiple distinct things (parse + validate + persist + notify)

Fix pattern: Extract each responsibility into its own class. Show the split.

O — Open/Closed Principle

Open for extension, closed for modification.

Violations to flag:

• if/else or switch chains on type/status that would require modification to add new types
• Hard-coded behaviour that should be configurable
• Direct instantiation of concrete classes in business logic (use interfaces)

Fix pattern: Introduce Strategy, Template Method, or polymorphism. Show the refactoring.

L — Liskov Substitution Principle

Subtypes must be substitutable for their base types.

Violations to flag:

• Subclass overrides a method by throwing UnsupportedOperationException
• Subclass weakens preconditions (accepts nulls when parent doesn't)
• Subclass strengthens postconditions (returns more restricted type)
• Square extends Rectangle anti-pattern

Fix pattern: Use composition over inheritance, or restructure the hierarchy.

I — Interface Segregation Principle

Clients should not depend on interfaces they don't use.

Violations to flag:

• Interfaces with more than ~5 methods where implementors only use some
• implements classes that leave methods empty or throw UnsupportedOperationException
• Fat service interfaces used by clients that only call 1–2 methods

Fix pattern: Split the fat interface into focused role interfaces.

D — Dependency Inversion Principle

Depend on abstractions, not concretions.

Violations to flag:

• Field or constructor takes a concrete class (new UserServiceImpl) instead of an interface (UserService)
• new ConcreteClass() inside business logic instead of dependency injection
• Static utility method calls deep in business logic that prevent testing
• @Autowired on a concrete class field instead of an interface

Fix pattern: Introduce interface + constructor injection. Show the change.

Output format

For each violation:

1. Principle violated: (S/O/L/I/D)
2. Location: class + method
3. Problem: what rule is broken and why it matters
4. Fix: before/after code

End with: SOLID Score — how many of the 5 principles are cleanly satisfied (e.g., "3/5 — S, I, D pass; O and L need attention").

Next Steps

• For O violations → run /java-design-pattern to find the right pattern
• For D violations → run /java-refactor to extract interfaces
• For SRP violations → run /java-refactor to split classes