Java/Java SE 15: What's New, Release History & Support Lifecycle

What Is New in Java 15

Java 15 delivers several key updates including finalized preview features, new language enhancements, and performance improvements. This release continues to refine the platform with a focus on developer productivity and application modernization.

Which Language Features Were Finalized in Java 15?

Java 15 finalized several preview features that were introduced in earlier releases. Text Blocks and Pattern Matching for instanceof are now standard, making them stable for production use without needing to enable preview features.

Sealed Classes remain in preview but have been updated based on community feedback. This model gives library authors precise control over which classes can extend or implement a sealed interface, a significant step for modeling complex domains.

How Do Records Improve Java Development?

Records are in their second preview, refining the shorthand for declaring data carrier classes. They automatically generate equals(), hashCode(), toString(), and accessor methods, drastically reducing boilerplate code.

In practice, this means you can define a simple data aggregate with a single line: record Point(int x, int y) { }. The refinements in this preview include support for local records and a more precise specification.

What Garbage Collector Improvements Are Included?

Both the Z Garbage Collector (ZGC) and the Shenandoah garbage collector are now production features. They were previously available as experimental options, but are now fully supported for use in production environments.

These low-pause-time GCs are a major benefit for applications where latency and responsiveness are critical. You can enable them with the -XX:+UseZGC or -XX:+UseShenandoahGC flags.

Are There Any New Low-Level APIs for Developers?

The Foreign-Memory Access API enters its second incubator stage, providing a safe and efficient way to access memory outside the Java heap. This is crucial for libraries that need to interact with native code and avoid the overhead of the Java Native Interface (JNI).

Hidden Classes are also now a standard feature. They are ideal for frameworks that generate classes at runtime, like Lambda expressions, as they are unobservable by reflection and have a limited lifecycle, which improves efficiency.

What Has Been Deprecated or Removed?

This release continues the cleanup of legacy features. The Nashorn JavaScript engine, along with its APIs, has been removed. Biased Locking and RMI Activation have been deprecated, signaling their eventual removal in a future release.

For most developers, these changes have minimal impact. The Nashorn removal primarily affects applications that embedded a JavaScript runtime; alternatives like GraalVM are the recommended path forward.