Java 25 Tutorial — Complete Guide

A complete Java 25 LTS tutorial series. Master every new feature — Flexible Constructor Bodies, Module Import Declarations, Scoped Values, Compact Object Headers, Generational Shenandoah, AOT Compilation, and more.

Java 25 Tutorial — Complete Guide

Java 25 is the LTS release where four years of preview work graduates to final API. Released September 16, 2025, it finalizes Scoped Values, Flexible Constructor Bodies, Module Import Declarations, Compact Source Files, and ships major performance wins via Compact Object Headers, Generational Shenandoah, and AOT Compilation. This series covers every feature — with runnable code examples and clear before/after comparisons.

12 articles. Every major JEP. Production-grade guidance throughout.

Part 1: Introduction and Setup

  1. Java 25: The LTS That Graduates Four Years of Previews
  2. Setting Up Java 25: Install, Tooling & IDE Configuration

Part 2: Language Features — Final

  1. Flexible Constructor Bodies (JEP 513): Validate Before super()
  2. Module Import Declarations (JEP 511): One Import to Rule Them All
  3. Compact Source Files & Instance Main Methods (JEP 512): Java as a Scripting Language

Part 3: Language Features — Preview

  1. Primitive Types in Patterns (JEP 507): Pattern Match Every Type

Part 4: Concurrency

  1. Scoped Values (JEP 506): The Final ThreadLocal Replacement
  2. Structured Concurrency (JEP 505): Preview 5 — What Changed?

Part 5: Performance & Runtime

  1. Compact Object Headers (JEP 519): 33% Less Heap Overhead
  2. Generational Shenandoah (JEP 516): Best GC for Low Latency
  3. AOT Compilation in Java 25 (JEP 514 & 515): Faster Startup, Zero Warm-Up

Part 6: Security

  1. Java 25 Security: Key Derivation Function API & PEM Encodings

What You Will Learn

  • How Flexible Constructor Bodies eliminates constructor workarounds by allowing validation and field initialization before super()
  • How Module Import Declarations replaces 20+ import lines with a single import module java.base;
  • How Compact Source Files let you write a complete Java program without a class declaration
  • How Scoped Values replaces ThreadLocal with an immutable, virtual-thread-safe alternative
  • How Structured Concurrency ensures no orphaned threads when parallel tasks fail
  • Why Compact Object Headers cut heap usage by ~10–20% with a single JVM flag
  • How Generational Shenandoah achieves sub-millisecond GC pauses on moderate heaps
  • How AOT Compilation cuts startup time 2–4× by caching JIT output across runs
  • The new KDF API for standard HKDF and PBKDF2 key derivation
  • How to use the PEM Encoding preview to read/write .pem files without Bouncy Castle

Prerequisites

  • Java programming experience — Java 17 or Java 21 recommended
  • Understanding of basic concurrency (threads, executors) for the concurrency articles
  • JVM basics (GC, heap) helpful for the performance articles

No prior Java 25 experience required.