Project Valhalla (Java language) explained

Project Valhalla is an experimental OpenJDK project to develop major new language features for Java 10 and beyond. The project was announced in July 2014 and is an experimental effort by Oracle, led by engineer Brian Goetz.^[1]

Planned features

Valhalla is incubating Java language features and enhancements in these areas:^[2]

• Value Types; highly-efficient small 'objects' without inheritance.
• Generic Specialization; List<int> for example.
• Reified Generics; retaining actual type at runtime.
• improved 'volatile' support.

These features will require both syntax and VM-level changes.

Project activity

The project is organized on the OpenJDK 'Project Valhalla' mailing list. Project Valhalla has begun in the experimental stages, with an inaugural announcement & early draft initial proposals.

Published as of January 2022:

• Project Valhalla announcement
• 'Value Types' initial proposal
• 'Generic Specialization' initial proposal
• State of Valhalla, Section 1: The Road to Valhalla
• State of Valhalla, Section 2: Language Model
• State of Valhalla, Section 3: JVM Model
• State of Valhalla, Section 4: Translation scheme

Experimental OpenJDK prototypes can also be built from the Mercurial repositories. These are starting to incorporate many specialization features. Note that these are Gnu Make/ C++ sources, and building the OpenJDK requires technical expertise. See OpenJDK build instructions for details.

• Project Valhalla OpenJDK source repositories

Project Components

The project is organized into several JEPs (JDK Enhancement Proposals):

• JEP Draft: Value Objects (Preview)
• JEP 401: Primitive Classes (Preview)
• JEP 402: Classes for the Basic Primitives (Preview)
• JEP draft: Universal Generics (Preview)

Value Classes

Value classes are reference types, in the same way as all existing Java classes. However, they give up the ability to have identity. This means that the

Notes and References

1. Web site: Goetz. Brian. Welcome to Valhalla!. OpenJDK mail archive. OpenJDK. 12 August 2014.
2. Web site: Evans. Ben. Oracle Launches Project Valhalla for Java. InfoQ. InfoWorld. 12 August 2014.