Java 8+, Object-Oriented Design, Exception Handling, Collections Framework, Concurrency (Threads), Streams, Lambdas, JUnit Testing, Clean Code Principles, Spring Boot, Spring Framework, Spring Security, Spring Cloud, Microservices Architecture, RESTful API Design, API Integration, Dependency Injection, Transaction Management, Spring Cloud Patterns, React (Hooks, JSX, Component Lifecycle, Component Composition), TypeScript, ES6+ JavaScript, HTML5, CSS3, Responsive Design, Accessibility (a11y), Redux, Context API, Redux Toolkit, State Patterns, API Contract Integration (OpenAPI/Swagger), Pagination, Error Handling, Authentication Flows (OAuth2/OIDC, JWT), Jest, React Testing Library, Cypress, Playwright, Unit Testing, Component Testing, End-to-End Testing, Test-Driven Development (TDD), React Performance Optimization, Code Splitting, Lazy Loading, Memoization, Efficient Rendering, Webpack, Vite, Environment Configuration, Bundle Optimization, PostgreSQL, MySQL, Hibernate/JPA, AWS (EC2, RDS), Docker, Git, CI/CD (Jenkins, GitHub Actions)