Object-oriented programming, JVM internals, multithreading, and Spring Boot microservices.
Master Java 21+: Object-Oriented Programming (OOP), JVM architecture, memory management, garbage collection, Collections framework, Generics, Concurrency & Virtual Threads, Spring Boot microservices, and Maven.
Bytecode compilation, JVM stack vs heap, and public static void main.
Primitive types (byte, int, long, double), wrapper classes, and BigDecimal for financial calculations.
if/else, switch expressions (Java 14+), for/while loops, and enhanced for-each.
Constructors, getters/setters, encapsulation, static members, and packages.
Extending classes (extends), super(), method overriding (@Override), and abstract classes.
Interface contracts, default methods, Java 21 Records, and sealed class hierarchies.
List (ArrayList, LinkedList), Set (HashSet, TreeSet), and Map (HashMap, ConcurrentHashMap).
Generic classes <T>, bounded type parameters (<T extends Comparable>), and wildcards (? extends Number).
Stream pipelines, map, filter, reduce, collect (Collectors.toList), and parallel streams.
Thread synchronization, ExecutorService, CompletableFuture, and Java 21 Virtual Threads.
Spring Boot 3, Dependency Injection, Spring Data JPA, and secure REST APIs.