For 0-1 Years of Experience (Freshers/Junior Developers):

• Core Java Fundamentals:
  • Data types, variables, operators
  • Control flow statements (if, else, switch, loops)
  • Methods and parameter passing
• OOP Concepts:
  • Classes, objects, constructors
  • Inheritance, encapsulation, polymorphism, abstraction
  • Method overloading and overriding
• Collections Framework:
  • List, Set, Map interfaces
  • ArrayList, LinkedList, HashSet, TreeSet, HashMap, LinkedHashMap
• Exception Handling:
  • try-catch, throw, throws, and finally
  • Checked vs unchecked exceptions
• String Handling:
  • String, StringBuilder, and StringBuffer
  • Common string operations (substring, length, etc.)
• Basic File I/O:
  • Reading and writing files using File, BufferedReader, and BufferedWriter
• Multithreading (Basics):
  • Creating threads (Runnable, Thread class)
  • Thread lifecycle
  • Synchronization basics

For 2-3 Years of Experience (Mid-Level Developers):

• Advanced OOP and Design Patterns:
  • SOLID principles
  • Common design patterns (Factory, Singleton, Builder, Observer, etc.)
  • Composition vs Inheritance
• Java Collections (Advanced):
  • Internal working of HashMap, HashSet, and TreeSet
  • Comparable vs Comparator
  • Collections utility class (Collections, Arrays, etc.)
  • Fail-fast vs fail-safe iterators
• Concurrency and Multithreading:
  • Thread safety, race conditions, and deadlock
  • Executors, Callable, and Future
  • Synchronized blocks, locks (ReentrantLock, ReadWriteLock)
  • volatile, ThreadLocal, and Atomic variables
• JVM Internals:
  • JVM architecture and components (ClassLoader, JIT, garbage collector)
  • Memory management (heap, stack, metaspace)
  • Garbage collection algorithms (CMS, G1)
• Generics:
  • Wildcards (? extends, ? super)
  • Bounded and unbounded types
  • Generic methods and classes
• Stream API:
  • Introduction to streams and functional programming in Java
  • Intermediate and terminal operations (filter, map, reduce)
  • Optional class and its usage

For 4-6 Years of Experience (Senior Developers):

• Concurrency (Advanced):
  • ConcurrentHashMap, CopyOnWriteArrayList, BlockingQueue
  • ForkJoinPool and parallel streams
  • CompletableFuture and asynchronous programming
• Memory Management (Advanced):
  • Deep dive into garbage collection (GC tuning, GC logs, troubleshooting)
  • JVM tuning and optimization