Early Access Release

The latest early access release of Valhalla features is published at https://jdk.java.net/valhalla/.

Functionality, language syntax, and class file formats are subject to change. Some supplementary tools and APIs do not fully support the new features. The goal of this release is to solicit feedback and establish a milestone as we work toward a preview release in Java SE.

This milestone is focused on specification conformance, and excludes some important performance optimizations. It is not intended to be used for performance benchmarking.

Value Classes and Objects

The features implemented by this release are described in JEP 401: Value Classes and Objects (Preview). (See the specification changes for more precise details.)

When preview features are turned on, Java programs can declare value classes and records, which have only final fields and lack object identity. At run time, the == operator compares value class instances according to their field values, without regard to when or where they were created. Other identity-sensitive operations are adjusted to appropriately work with objects that lack identity.

By enabling preview features, developers also get value-class versions of java.lang.Integer, java.time.LocalDate, java.util.Optional, and a handful of other classes in the standard libraries. Developers are encouraged to test their code against these modified libraries, and to experiment with their own value-candidate classes.

Please provide any feedback to valhalla-dev@openjdk.org.

Notes

This release lacks some important performance optimizations, and should not be used for performance benchmarking.
The JEP includes some helpful guidance on the migration of existing classes.
Deserialization of a value class is only supported by the ObjectInputStream API if the class is a record class or is instantiated via readResolve. Improved support for deserialization will be coming later.
On macOS, after expanding the tar.gz archive, you may need to remove the quarantine attribute from the bits before commands can be executed. Use Terminal to execute the following command:
```
xattr -d com.apple.quarantine ./jdk-23.jdk
```