SOLID Principles

SOLID is most useful when it guides concrete refactoring decisions. In Java, the principles help teams decide when a class has too many reasons to change, when extension points are stable, and when dependencies should be represented by interfaces or capabilities instead of concrete classes.

Use this section as a design review checklist rather than a rulebook. Each principle has trade-offs, especially when abstraction arrives before the code has earned it.

In this section

• Single Responsibility Principle in Java
  Split Java classes around real reasons to change so behavior, persistence, validation, and presentation do not collapse together.
• Open/Closed Principle in Java
  Extend Java behavior through stable seams such as interfaces, strategies, and decorators without modifying code that should stay closed.
• Liskov Substitution Principle in Java
  Design Java subtypes that preserve caller expectations so inheritance and polymorphism remain safe to use.
• Interface Segregation Principle in Java
  Keep Java interfaces focused so callers depend only on the operations they actually need.
• Dependency Inversion Principle in Java
  Invert Java dependencies around stable abstractions so policy code does not depend directly on volatile implementation details.