Learning paths

Crack the Java interview

The topics interviewers ask about most, from equals and HashMap internals to concurrency, data structures, Spring and system design.

  • For: You have a Java developer interview coming up.
  • By the end: You can explain the classic Java questions clearly and solve common coding problems.
  • Size: 28 lessons (1 h 28 min of reading, plus time to try the code), intermediate to advanced
Start with equals(), hashCode() and the Object contract
  1. Strings, StringBuilder and text blocksJava fundamentals, beginner, 4 min
  2. Immutable objectsObject-oriented programming, intermediate, 3 min
  3. How HashMap works insideCore APIs, advanced, 3 min
  4. Collections framework: choosing the right oneCore APIs, intermediate, 3 min
  5. Sorting objects: Comparable and ComparatorCore APIs, intermediate, 3 min
  6. Generics and wildcardsCore APIs, intermediate, 3 min
  7. Exception handlingCore APIs, intermediate, 5 min
  8. Stream APIModern Java, intermediate, 3 min
  9. Collectors: grouping, partitioning and joiningModern Java, intermediate, 3 min
  10. Threads and ExecutorServiceConcurrency and the JVM, intermediate, 3 min
  11. synchronized, volatile and locksConcurrency and the JVM, advanced, 4 min
  12. Concurrency utilities: latches, semaphores and atomicsConcurrency and the JVM, advanced, 3 min
  13. CompletableFutureConcurrency and the JVM, advanced, 3 min
  14. Virtual threadsConcurrency and the JVM, advanced, 3 min
  15. JVM memory and garbage collectionConcurrency and the JVM, advanced, 3 min
  16. Big-O: how fast is your code?Data structures and algorithms, beginner, 3 min
  17. Sorting and searchingData structures and algorithms, intermediate, 3 min
  18. Linked lists, stacks and queuesData structures and algorithms, intermediate, 3 min
  19. Trees and graphsData structures and algorithms, intermediate, 3 min
  20. Dynamic programmingData structures and algorithms, advanced, 3 min
  21. SOLID principlesDesign and clean code, intermediate, 3 min
  22. Design patterns: Singleton, Factory and BuilderDesign and clean code, intermediate, 3 min
  23. IoC and dependency injectionSpring Core and Spring MVC, intermediate, 3 min
  24. Transactions, propagation and lockingJDBC, JPA and Hibernate, advanced, 3 min
  25. The N+1 problem (and how to fix it)JDBC, JPA and Hibernate, advanced, 3 min
  26. Spring Security and JWTSpring Boot, advanced, 3 min
  27. Monolith vs microservicesMicroservices, intermediate, 3 min

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