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Oracle Java SE 21 study guide

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Lessons

  1. Concurrent Collections, Atomics, and Explici
  2. Concurrency Utilities: ExecutorService, Call
  3. Thread Safety, Synchronization, and the Java
  4. Thread Fundamentals, Creation, and Lifecycle
  5. Virtual Threads in Java 21 — Free Study Guide 2026
  6. Conditional Logic: if-else and Ternary Opera
  7. Loops and Branching Statements — Free Study Guide 2026
  8. Pattern Matching for switch and instanceof
  9. Switch Statements and Switch Expressions
  10. Java Annotations: Built-in, Meta-Annotations
  11. Custom Exceptions and Best Practices — Free Study Guide 2026
  12. Exception Hierarchy: Checked vs. Unchecked E
  13. Exception Handling: try, catch, finally, and
  14. Resource Management: try-with-resources and
  15. Built-in Functional Interfaces in java.util.
  16. Lambda Expressions, Variable Scopes, and Eff
  17. Method References: Four Varieties and Edge C
  18. Working with java.util.Optional — Free Study Guide 2026
  19. Arrays: Creation, Multidimensional Forms, an
  20. Core Collections: Lists, Sets, Queues, and M
  21. Wildcards, Type Bounds, and Type Erasure
  22. Generics Fundamentals and Generic Methods
  23. Sequenced Collections in Java 21 — Free Study Guide 2026
  24. Sorting, Comparable, and Comparator — Free Study Guide 2026
  25. Date and Time APIs — Free Study Guide 2026
  26. Operators, Precedence, and Type Casting
  27. Strings, Text Blocks, and StringBuilder
  28. Program Structure, Primitives, Literals, Sco
  29. Classic Java I/O Streams and Readers/Writers
  30. Java NIO.2 File API: Path, Paths, and File S
  31. Advanced NIO.2 Stream Operations and Directo
  32. Java Object Serialization and Record Seriali
  33. Modular Compilation, Packaging, and CLI Exec
  34. Module Architecture and module-info.java Dec
  35. Module Directives: requires, exports, opens,
  36. Module Types, Migration Strategies, ServiceL
  37. Formatting and Parsing Numbers, Currencies,
  38. Locales and Resource Bundles — Free Study Guide 2026
  39. Java Enums: Fields, Methods, and Abstract Co
  40. Advanced Record Patterns, Nested Deconstruct
  41. Java Records, Canonical/Compact Constructors
  42. Sealed Classes and Interfaces: permits, fina
  43. Abstract Classes and Interfaces — Free Study Guide 2026
  44. Class Declarations, Constructors, and Object
  45. Encapsulation and Access Modifiers — Free Study Guide 2026
  46. Inheritance, Method Overriding, and Polymorp
  47. Method Overloading, Overload Resolution, and
  48. Nested, Inner, Local, and Anonymous Classes
  49. Advanced Collectors, Grouping, Partitioning,
  50. Primitive Streams and Parallel Stream Proces
  51. Stream Creation and Intermediate Operations
  52. Terminal Operations and Reductions — Free Study Guide 2026