← Theory library
Core Java theory
Language fundamentals, collections and OOP.
Easy
- 1. Java Syntax BasicsIntroduction to Java syntax, semicolons, and curly braces.
- 2. Data TypesPrimitive and reference types in Java.
- 3. Variables and ConstantsDeclaring variables and using final for constants.
- 4. Control Flow: If-ElseConditional branching in Java.
- 5. Loops: For and WhileIterating through blocks of code.
- 6. ArraysFixed-size data structures.
- 7. Classes and ObjectsThe building blocks of Java.
- 8. MethodsDefining behavior for objects.
- 9. ConstructorsSpecial methods for initialization.
- 10. EncapsulationHiding data using access modifiers.
- 11. InheritanceReusing code across classes.
- 12. PolymorphismOne interface, multiple forms.
- 13. AbstractionHiding implementation details.
- 14. InterfacesDefining a contract.
- 15. Static KeywordClass-level members.
- 16. This and SuperReferencing current and parent instances.
- 17. Method OverloadingSame name, different parameters.
- 18. Method OverridingRedefining parent behavior.
- 19. Exception HandlingDealing with runtime errors.
- 20. StringsWorking with text.
Medium
- 21. Generics BasicsType safety for classes and methods.
- 22. Wrapper ClassesObjects for primitives.
- 23. ArrayListResizable arrays.
- 24. HashMapKey-value mapping.
- 25. HashSetCollection of unique elements.
- 26. LinkedListDoubly-linked data structure.
- 27. Comparable and ComparatorSorting objects.
- 28. Functional InterfacesInterfaces with one abstract method.
- 29. Lambda ExpressionsAnonymous functions.
- 30. Method ReferencesShorthand for lambdas.
- 31. Streams API IntroProcessing sequences of elements.
- 32. Stream: filter() and map()Transforming and selecting data.
- 33. Stream: collect()Gathering results into a collection.
- 34. Optional ClassAvoiding NullPointerExceptions.
- 35. EnumsFixed set of constants.
- 36. AnnotationsMetadata for code.
- 37. File I/O BasicsReading and writing files.
Hard
- 38. Threads and RunnableIntroduction to multi-threading.
- 39. SynchronizationPreventing race conditions.
- 40. Volatile KeywordMemory visibility.
- 41. Thread LifecycleStates of a thread.
- 42. Executor ServiceManaging thread pools.
- 43. Callable and FutureThreads that return results.
- 44. DeadlockWhen threads wait forever.
- 45. Reflection APIInspecting code at runtime.
- 46. Garbage Collection BasicsAutomatic memory management.
- 47. Inner ClassesClasses within classes.
- 48. Try-with-resourcesAutomatic resource management.
- 49. SerializationSaving object state.
- 50. Java Modules (Jigsaw)Project structure at scale.