A Java String.format cheat sheet where every output was run on JDK 25: specifier anatomy, padding and alignment, why %.2f can disagree with C, locale traps, the lakh/crore grouping Formatter cannot produce (with a working formatter), the exceptions it throws, and what it costs against +.
Fifty Java interview questions for freshers answered in plain language, each with real code and the exact output it printed on JDK 25: OOP, strings, collections, exceptions, Java 8 to 25 features and threads, with the traps interviewers love.
Koog 1.3.0 in plain Java: a two-tool agent, the exact HTTP requests it sends, what happens when a tool throws or a model loops, a strategy graph with a Java step before the model, and the Spring Boot starter with the Kotlin BOM trap. Tested against a scripted OpenAI-compatible endpoint; every transcript is committed.
Most MCP servers stop at tools. This post builds an incident-desk server in Java with resources, a prompt, sampling and elicitation on Spring AI 2.0.2 and MCP SDK 2.1.0, then breaks it on purpose: a client without the capability, a slow client, a stateless server that silently drops every tool, and what the 2026-07-28 spec changes.
Learn sliding window and two pointers in Java through 12 classic interview problems: fixed vs variable windows, step-by-step dry runs, brute-force cross-checks and operation counts, all from real JDK 25 runs.
Learn dynamic programming in Java from scratch: memoization vs tabulation vs space-optimised tables on ten classic problems (Fibonacci, coin change, knapsack, LCS, edit distance and more), with recursion diagrams, tested code and exact output.
A beginner-first JMH tutorial, verified on JDK 25 and JMH 1.37: dead-code elimination, Blackhole, constant folding, warmup, forks, state scopes, -prof gc and percentiles, each shown with real captured output.
Four ways to keep a password out of your Spring Boot code, each run for real on Boot 4.1.2: what happens when the secret is missing, how rotation behaves, and five ways the value leaks anyway.
Build an MCP server with only the official Java SDK 2.1.0: tools and resources, a fat jar for Claude Desktop over stdio, Streamable HTTP on Jetty, and a Spring AI client connecting to it. Every output comes from a committed transcript.
A client times out and retries a payment. Build Stripe-style Idempotency-Key handling in Spring Boot 4.1 with a Redis store and a Postgres store, and see what each does with replays, changed bodies, concurrent duplicates, expiry and a crash.