Mastering Java 21 – All New Features Since Java 17

In this two-day course, you'll learn all the essential new features introduced in Java versions 18 through 21 – compact, hands-on, and clearly explained.

We focus on modern language features like Record Patterns, Pattern Matching for switch, and the new Sequenced Collections API. You’ll see how these features help make your code cleaner, more expressive, and easier to maintain.

We’ll also explore numerous standard API improvements, garbage collection optimizations, and under-the-hood performance enhancements – all of which can provide real benefits in your day-to-day work.

Through hands-on exercises based on real-world project scenarios, you'll apply what you've learned immediately and internalize it for the long term.

To wrap up, we’ll look at what’s ahead: Structured Concurrency, Scoped Values, and the Foreign Function & Memory API are still preview features in Java 21 – but they already hint at where Java is heading.

Request in-house training »

This course is for Java developers who want to stay up to date or deepen their knowledge of Java 21 – clear, hands-on, and packed with aha moments.

Whether you're planning a migration to Java 21 or already have some experience with it, you'll learn how to effectively leverage the new language features, API enhancements, and performance improvements in your everyday work.

The course is also ideal for teams already using Java 21 in production and looking to dive deeper into specific features or best practices.

We won’t follow the listed order strictly. Instead, we’ll alternate between major features, smaller topics, and theory – keeping the course engaging and balanced, and helping you better retain the material.

Major Features:

• Virtual Threads
• Sequenced Collections
• Record Patterns
• Pattern Matching for switch

Additional Features:

• UTF-8 by default
• Simple web server
• Code snippets in Java API documentation
• New system properties for System.out and System.err encoding
• Compiler warnings for lossy type casts
• Key Encapsulation Mechanism API

Bugfixes:

• IdentityHashMap's remove() and replace() methods use object identity

API Enhancements:

• New methods for String, StringBuilder, and StringBuffer
• New methods for Character
• New methods for Math
• HashMap.newHashMap()
• Additional date-time formats

Garbage Collection:

• String deduplication for ZGC, SerialGC, ParallelGC
• G1 enhancements
• Generational ZGC

Performance:

• Alternative fast-locking scheme

Deprecations & Removals:

• Deprecate finalization for removal
• Locale constructors
• URL constructors
• Thread.stop(), suspend(), resume()
• ThreadGroup
• Dynamic loading of agents

Looking Ahead:

• Structured Concurrency
• Scoped Values
• Vector API
• Foreign Function & Memory API
• Unnamed Patterns and Variables
• Comptact Classes and Instance Main Methods