Technology
12 min read
How Java's collections framework is organised, how ArrayList and LinkedList really differ, what makes a Set unique, how to remove items safely while iterating, and the confusing differences between List.of, Arrays.asList and unmodifiable views. Includes sequenced collections from Java 21.
Technology
12 min read
How Java reports and handles errors: the exception hierarchy, checked versus unchecked exceptions and why opinions differ, try, catch, finally and try-with-resources, custom exceptions, exception chaining, and the habits that separate good exception handling from swallowed errors.
Technology
12 min read
How to model data precisely in modern Java: enums for fixed sets of values, records for immutable data carriers, and sealed types with pattern matching for a closed set of alternatives. Each is introduced from the bug it prevents, and compared with the older style you will still see.
Technology
13 min read
Why Java strings are immutable and what the string pool really is, when to use StringBuilder, how Unicode makes length surprising, how text blocks and formatting work, and how to handle dates and times with java.time instead of the old Date and Calendar. Includes testable time with Clock.
Technology
12 min read
Why two objects that look identical are not equal by default, what == really compares, how to write equals and hashCode correctly, why mutable keys break HashSet and HashMap, and how immutability makes all of this safer. Includes the Integer cache surprise and the contracts interviewers ask about.
Technology
13 min read
Starting from a payment system full of if-else branches, this article shows why interfaces and polymorphism exist, how abstract classes differ from interfaces, what default methods are for, and why composition usually beats inheritance. It also previews the idea behind dependency injection.
Technology
11 min read
How one Java class can build on another, how overriding changes behaviour at runtime, how overloading is chosen at compile time, and why inheritance is easy to misuse. With the constructor-order trap, field hiding and the exact differences interviewers ask about.
Technology
12 min read
Why object-oriented programming exists and how Java expresses it: classes as blueprints, objects as instances, constructors, access modifiers, static versus instance members, and encapsulation as a way to protect the rules of your data. Built around a bank account that cannot go wrong.
Technology
13 min read
How to make a Java program choose and repeat: if, switch (old statement and modern expression), the loop forms, and how to organise code into methods. Includes the pass-by-value rule that interviewers love and the scope rules that cause mysterious compile errors.
Technology
15 min read
How Java stores and combines data: primitive types versus references, what happens when a number overflows, why integer division surprises people, how casting and conversion work, when to use var, and how arrays hold a fixed number of values.
Technology
15 min read
What Java actually is, how a .java file becomes a running program, what the JDK, JRE and JVM each do, and how to compile and run your first program. Plus the full roadmap of this 41-article course, from zero to a tested Spring Boot API.
CourseTechnology
A free 41-article course that takes you from your first Java program to a tested, secured Spring Boot and PostgreSQL backend, with three projects, real verified output and interview preparation. Modern Java 21 and later, with older styles labelled.
Technology
14 min read
Turn the course into interview performance: an eight-week practice plan, how to run timed solo drills and mock interviews, a self-scoring rubric that separates SDE-1 and SDE-2 expectations, a drill sheet for the twelve classic problems, ten new practice problems to test transfer, common failure patterns, and the complete job-ready checklist.
Technology
17 min read
An educational design for searching a billion web pages: a polite, distributed crawler with a URL frontier and robots.txt, deduplication, building an inverted index with batch processing, document-partitioned shards and replicas, scatter-gather query serving with result caching and tail-latency control, ranking from relevance and link signals, freshness tiers, failures and safety.
Technology
16 min read
Design an online store from product pages to delivery: a catalogue and search served from caches and event-fed indexes, carts in a key-value store, inventory reservations with expiry, a checkout saga across inventory and payment, oversell prevention, and a flash sale that survives a thousandfold spike with a waiting room, bucketed stock and isolation from normal shopping.
Technology
17 min read
Design a food delivery platform where every order coordinates three parties in real time: restaurant discovery and menus as cached read models, an idempotent checkout, an order state machine driven by a saga with timeouts and compensations, dispatching delivery partners timed to food readiness, batching, live tracking, notifications, dinner-peak load, failures and the trade-offs between them.
Technology
18 min read
Design the core of a ride-hailing app: ingesting hundreds of thousands of driver location updates per second, a geospatial index of available drivers, matching riders to drivers with offers and timeouts, never assigning one driver twice, a trip state machine, live tracking for riders, city-based partitioning, payments, failures, privacy and fraud.
Technology
15 min read
Design an on-demand video platform: resumable uploads straight to object storage, a parallel transcoding pipeline that splits videos into chunks and renditions, adaptive bitrate streaming with HLS-style segments and manifests, CDN delivery at terabits per second, storage tiering, view counting, failures, content safety and the metrics that matter to viewers.
