9 minutes / published
Java 25 for Kotlin Developers
The actual delta: syntax, runtime model, and the places Java is explicit on purpose.
Start With Translation, Not Taste
A Kotlin developer does not need a beginner Java tutorial. They need a map of instincts that no longer transfer cleanly.
Records are not data classes with worse defaults. Optional is not nullable syntax with angle brackets. Streams are not Kotlin collections with a different method naming convention.
Records Are Boundary Tools
Use records for DTOs, value returns, and teaching small immutable shapes. Do not make them JPA entities in this course.
That restriction is not ceremony. Hibernate wants identity, lifecycle, and mutability stories that records intentionally avoid.
Virtual Threads Are Not Coroutines
Virtual threads let blocking-looking code scale differently. They do not add suspend markers, structured concurrency by default, or coroutine-style cancellation semantics.
That difference is an asset for backend work. It lets the article explain the runtime model instead of pretending two ecosystems reached the same abstraction.