Java’s OpenJDK project contemplates the inclusion of computed constants. These are immutable data containers, initialized once at most, which marry the efficiency and safety traits of final fields to a broader initialization window.

Currently in its preliminary phase, this proposal aims to be a standard in Java. The underlying principle is to “embrace immutability,” which brings along a slew of benefits. A consistently constructed immutable object has a singular, defined state. These objects can be shared safely, even with potentially harmful code. Plus, their very nature opens doors to various runtime optimization techniques.

While final fields are Java’s primary method to handle immutability, they aren’t without constraints. Hence, developers often find themselves juggling the benefits of immutability with flexibility concerning initialization time. Several workarounds exist, but they aren’t foolproof. To bridge this gap, the computed constants API offers class and interface definitions. This lets applications and libraries seamlessly create and deploy computed constant objects and their collections. It’s part of the java.lang package within the java.base module.

Key Objectives of this Move:

• Unlinking computed constant’s initialization from their host object or class.
• Presenting a user-friendly API for these constants and their sets.
• Encouraging optimization techniques like constant folding for these constants while facilitating dataflow interdependencies.
• Minimizing the code required for static initializers or field setups.
• Separating the intricacies of <clinit> dependencies using the methods mentioned above.
• Ensuring reliability and coherence, especially in parallel computing scenarios.

This initiative doesn’t aim to offer extended language features for constant calculations or discourage current methods of lazy initialization.

Considering that the features for the upcoming Java Development Kit 21 have been finalized and is set for a September launch, the earliest we might see computed constants in standard Java is in JDK 22, which is anticipated for March 2024.