Java 25 Features Deep Dive: What has changed since Java 21 LTS

1️⃣ Primitive Types in Pattern Matching (JEP 507)

• Java now supports primitive type patterns (e.g. int, double, char, boolean) in instanceof, pattern matching, and switch contexts.
• This eliminates boilerplate of boxing/unboxing in many conditional and switch constructs.

2️⃣ Compact Object Headers

• Java 25 introduces an option to use compact object headers, shrinking the object header from 12 bytes to 8 bytes on 64-bit JVMs.
• This optimization reduces heap footprint, improves memory density, and enhances cache locality — especially helpful for large heaps or data-intensive apps.
• You must enable it with a JVM flag, e.g. -XX:+UseCompactObjectHeaders.

3️⃣ Vector API (7th Incubator, JEP 508)

• Vector API continues as an incubator in JDK 25 (this is perhaps the 10th incubator iteration).
• The goal: let you express vectorized (SIMD) computations in Java which the JIT or runtime can map to optimal hardware instructions, giving better throughput than scalar loops.
• Example use cases: bulk numerical operations, matrix transforms, graphics, cryptography, data analytics pipelines.

4️⃣ Key Derivation Function (KDF) API

• JDK 25 adds a dedicated KDF API to streamline cryptographic key derivation (e.g. PBKDF2, HKDF).
• Instead of juggling SecretKeyFactory, PBEKeySpec etc., you can derive a key via a unified API.

5️⃣ Ahead-of-Time (AOT) Profiling and Compilation

• Java 25 introduces enhanced AOT method profiling to optimize startup times and resource usage in microservices, containers, serverless, and cold-start environments.
• There is also a related JEP for Command-Line Ergonomics (JEP 514) to simplify usage of AOT tooling.
• With profiling, the runtime can decide which methods to AOT compile, which to leave for JIT, and better balance between startup performance and peak throughput.

6️⃣ Flexible Constructor Bodies

• You can now write statements before calling super() or this() in a constructor — earlier this was forbidden.
• But such statements must not reference this (the object) before the constructor call; they are allowed to initialize fields or validate arguments.
• This helps with cleaner validation, early checks, and reducing boilerplate of “pre-super logic” hacks.

7️⃣ Other Noteworthy Features You Might Add

• Scoped Values (JEP 506, preview) — a lighter, safer alternative to ThreadLocal, for passing immutable context values across call boundaries and threads.
• Module Import Declarations (JEP 511) — you can import module ... to bring in all its exported packages, more concise modular code.
• Compact Source Files & Instance Main Methods (JEP 512) — simplify Java “scripts” by removing boilerplate class declarations and making main methods instance methods.
• Removal of 32-bit x86 Port (JEP 503) — support for 32-bit x86 is removed.
• Enhanced JFR (Java Flight Recorder) features — cooperative sampling (JEP 518), better method timing & tracing (JEP 520)
• Generational Shenandoah (JEP 521) — improvements in the garbage collector.