#java-21

5 post(s)

Sequenced Collections:First, Last, and Reversed Without the Ceremony

Learn how Java 21 sequenced collections provide uniform first, last, and reversed operations across lists, deques, ordered sets, and ordered maps.

Spring Boot

Spring Boot Virtual Threads:Flip One Flag, Then Fix What Breaks

Enable spring.threads.virtual.enabled on Boot 3.2+, understand what Tomcat and the application task executor actually switch, and size Hikari, RestClient, and observability so the flag does not become a thundering herd.

Java

Sealed Classes + Pattern Switch:Exhaustive Code Without `instanceof` Soup

What sealed classes are (JEP 409 / Java 17), how pattern switch and record patterns finish the story on Java 21, and how to replace cascading instanceof with compiler-checked exhaustiveness.

Java

Locks After Loom:When `synchronized` Still Wins

After virtual threads, when intrinsic locks still win — pinning vs JEP 491, wait/notify, monitors, and ReentrantLock — so you do not treat synchronized as obsolete.

Java

Virtual Threads:Millions of Tasks Without a Thread Pool Circus

What Java virtual threads are (JEP 444 / Java 21), how they differ from platform threads, when they win for I/O-bound work, and the pinning and ThreadLocal gotchas—plus what Java 25 changed.