Java Revision

Overview

This checklist covers essential Java concepts required for building enterprise-grade backend services and excelling in technical interviews. Review each topic and tick items off as you verify your understanding.

Tip: Don't just read definitions — write short code snippets or REPL experiments for any topic where you hesitate on syntax, internal working, or trade-offs.

Basics Refresh

• Variables, data types, type casting
• Operators (arithmetic, logical, bitwise)
• Control flow — if/else, switch, ternary
• Loops — for, while, do-while, for-each
• Arrays — single & multi-dimensional
• Strings — String, StringBuilder, StringBuffer, key methods

OOP Refresh

• Classes, Objects, Constructors (this, super)
• Encapsulation — access modifiers, getters/setters
• Inheritance — extends, method overriding, super
• Polymorphism — compile-time vs runtime
• Abstraction — abstract classes vs interfaces (when to use which)
• static & final keywords
• Enums, Wrapper classes, Autoboxing

Exception Handling Refresh

• try/catch/finally, multi-catch
• Checked vs Unchecked exceptions
• Custom exceptions, throws vs throw

Collections Framework Refresh

• ArrayList vs LinkedList vs Vector — when to use
• HashMap vs TreeMap vs LinkedHashMap — internals
• HashSet vs TreeSet vs LinkedHashSet
• Queue, Deque, PriorityQueue
• Comparable vs Comparator
• Iterators, Collections utility class
• Generics — generic classes, methods, bounded types, wildcards

Java 8+ Features Refresh (Critical for interviews)

• Lambda expressions
• Functional interfaces — Predicate, Function, Consumer, Supplier
• Stream API — filter, map, reduce, collect, flatMap, groupingBy
• Optional — of, ofNullable, orElse, map, flatMap
• Method references
• var keyword (Java 10+)
• Records (Java 14+)
• Sealed classes (Java 17+)
• Pattern matching for instanceof (Java 16+)

Multithreading Refresh

• Thread class, Runnable, Callable
• synchronized, volatile
• ExecutorService, Thread pools
• CompletableFuture — thenApply, thenCompose, allOf
• ConcurrentHashMap, thread-safe collections

File I/O & Serialization

• BufferedReader, Files, Path class
• Serialization / Deserialization
• try-with-resources