What Hibernate 8's EntityAgent is, how it differs from EntityManager, and what it really does on 8.0.0.CR1: no dirty checking, lazy fetch(), bulk inserts, lock modes, programmatic result set mappings, and where H2 and HSQLDB disagree. Every figure comes from a committed test run.
A Java DateTimeFormatter cheat sheet where every output was run on JDK 25: pattern letters, why YYYY prints next year in late December (36 wrong days in 11 years for en_US and en_IN), the U+202F space that breaks AM/PM parsing since JDK 20, SMART vs STRICT parsing of 31 February, ISO constants, and a shared SimpleDateFormat that returns wrong dates.
Spring Data JPA projections, tested on Spring Boot 4.1.2 and Hibernate 7.4: closed and open interface projections, record DTOs, dynamic projections and @Query constructor expressions, with the real SQL Hibernate generated for each, the @Value trap that loads full rows, and three @Query traps that fail quietly.
Learn stack and queue problems in Java from scratch: balanced brackets, RPN, min stack, next greater element, largest rectangle in a histogram, decode string, queue from two stacks and stack from one queue, with dry runs, brute-force cross-checks and operation counts from real JDK 25 runs.
Copying an object does not copy what it points at. A run-it-yourself walk through shallow vs deep copy in Java: why clone() is broken, copy constructors, serialization copies, records and defensive copies, with real output from a 24-test companion module.
Why Java needs both equals() and hashCode(), shown by breaking them: a HashSet holding duplicates, a constant hash costing 2,002,999 comparisons for 2,000 lookups, a mutated key that get() and remove() cannot find, record edge cases, and the JPA entity id trap. Every output is from a JDK 25 run and a committed transcript.
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.