Core Java
Fundamentals to advanced: theory, scenarios and follow-up traps.
1. Java Basics
JVM, JDK/JRE, class loading, memory areas, data types, operators, static/final/volatile, initialization order, modern syntax and the classic gotchas.
2. OOPs (Design-Focused)
Four pillars, interfaces vs abstract classes, sealed types and records, overriding rules, init order, equals/hashCode, immutability, SOLID, nested classes, enums, generics and access control.
3. Multithreading & Concurrency
Thread lifecycle, synchronization, the Java Memory Model, locks, atomics, executors, CompletableFuture, concurrent collections, virtual threads and classic race-condition scenarios.
4. Java Networking
TCP and UDP, blocking sockets, NIO selectors and buffers, Netty, Java 11 HttpClient, HTTP/1.1 vs HTTP/2, TLS, DNS caching, timeouts, pooling, CORS, proxies, WebSockets, backpressure, and debugging hangs, resets and slow calls.
5. Exception Handling
Throwable hierarchy, checked vs unchecked, try/catch/finally semantics, try-with-resources, custom exceptions, translation, errors, performance, logging, concurrency, REST error handling and transaction rollback rules.
6. Java Collections Framework
List, Set, Map, Queue and Deque hierarchy, HashMap internals, ordering, fail-fast iteration, immutable and concurrent collections, sequenced collections and real-world pitfalls.
7. Strings & Regular Expressions
String immutability, the string pool and intern, StringBuilder, compact strings, concatenation, text blocks, Unicode and charsets, formatting, hashing, security, regex engine behaviour, ReDoS and tricky output questions.
8. Advanced Java
JVM memory model, garbage collectors and tuning, diagnostics tooling, memory leaks, class loading, JIT, references, generics, JPMS, native interop, low-level performance, OOM scenarios, containers and JMH.
9. File I/O & Serialization
Streams vs readers, buffering, NIO.2, memory-mapped files, large file processing, charsets, Java serialization and its security risks, JSON vs Protobuf/Avro, zip handling, atomic writes and real-world file failure scenarios.
10. Annotations & Reflection
Built-in and custom annotations, retention and targets, annotation processing and Lombok, the Reflection API, modules and setAccessible, MethodHandles, dynamic proxies, runtime generics, framework usage, security and GraalVM native image.
11. JDBC
JDBC architecture, drivers, statements, ResultSet, SQL injection, batching, transactions and isolation, HikariCP pooling, streaming, LOBs, locking, retries and production debugging.
12. Java Testing (JUnit, Mockito)
Test pyramid, JUnit 5, AssertJ, Mockito, test doubles, TDD, Spring Boot test slices, Testcontainers, contract testing, flaky tests, concurrency and time testing, coverage and mutation testing.
13. Web Development
Servlet lifecycle, filters, listeners, sessions, MVC, HTTP semantics, caching, REST, CORS/CSRF/XSS, authentication, JWT/OAuth2, async servlets, embedded servers, API design and production web scenarios.
14. Java 8 & Functional Programming
Lambdas, functional interfaces, method references, Stream API semantics and pitfalls, collectors, Optional, Date/Time API, default methods, CompletableFuture and the records, pattern matching and sealed types added in Java 14-21.
15. Design Patterns (Backend-Relevant)
Creational, structural and behavioral patterns as used in Java backends and Spring, plus dependency injection, repository/DTO, CQRS, outbox, saga, circuit breaker, idempotency, anti-patterns and functional alternatives.
16. Java Security
JCA/JCE, hashing vs encryption vs signing, password hashing, AES-GCM, RSA/ECDSA, SecureRandom, TLS and keystores, OWASP Top 10 for Java, secrets, JWT pitfalls, SecurityManager removal, supply chain and incident scenarios.
17. Cloud Computing Fundamentals
Service models, regions and AZs, shared responsibility, IAM, VPC networking, load balancing, autoscaling, storage and databases, messaging, serverless and Java cold starts, twelve-factor, containers, cost, HA/DR, observability and cloud incident scenarios (AWS-focused).
18. Spring Framework & Hibernate
Fundamentals of Spring IoC/DI, bean scopes, AOP proxies, Spring MVC, Boot auto-configuration, JdbcTemplate, JPA/Hibernate entity lifecycle and mappings, transactions, Spring Data, validation, testing and actuator.