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🛠️ Testing, Tools & Ecosystem

14 Java concepts, each explained step by step with real code, a common trap and practice questions.

  1. Unit testing with JUnit 5@Test, assertions, assertThrows, lifecycle annotations, parameterized tests.
  2. Mocking with MockitoMocks vs stubs vs fakes, when/thenReturn, verify, not mocking what you don't own.
  3. Test-driven developmentRed, green, refactor; the test pyramid.
  4. Mavenpom.xml, coordinates, lifecycle phases, dependency scopes.
  5. GradleBuild scripts, tasks, configurations like implementation vs api.
  6. Dependencies & versionsTransitive dependencies, conflicts, semantic versioning, vulnerability scanning.
  7. Packaging & runningJAR, executable JAR, classpath, jlink custom runtimes, jpackage.
  8. LoggingSLF4J facade, log levels, parameterized messages vs string concatenation.
  9. JDBCConnection, PreparedStatement (prevents SQL injection), ResultSet, transactions, connection pools.
  10. JPA & Hibernate conceptsEntities, persistence context, lazy loading, the N+1 query problem.
  11. Spring Boot conceptsIoC container, beans, auto-configuration, REST controllers.
  12. Writing secure JavaInput validation, injection, unsafe deserialization, secrets handling.
  13. Performance & profilingMeasure first, JMH micro-benchmarks, boxing and allocation costs.
  14. GraalVM & native imagesAhead-of-time compilation, fast startup, reflection limitations.