A proposed API for 'stable values' in Java is set to revolutionize the way Java applications initialize, promising significant improvements to startup times. The Java Enhancement Proposal (JEP), updated on January 24, outlines a new approach to object initialization that combines the benefits of immutable state with flexible timing.

Stable values, as described in the JEP, are objects that hold immutable data, similar to constants. However, unlike final fields, stable values offer greater flexibility in terms of initialization timing. This flexibility enables the JVM to apply the same performance optimizations as it would with final fields, but without the limitations. As a result, Java application startup times are expected to improve dramatically.

The proposal's primary goals include decoupling the creation of stable values from their initialization, ensuring that stable values are initialized no more than once, even in multi-threaded programs, and enabling user code to take advantage of constant-folding optimizations previously only available to JDK-internal code. Notably, the proposal does not aim to introduce a new way to declare stable values or alter the semantics of final fields.

The motivation behind the stable values proposal lies in the advantages of immutability. As the JEP notes, immutable objects can be shared freely across multiple threads, making them an attractive solution for many real-world applications. However, final fields, the Java platform's current tool for managing immutability, have limitations, such as the need to be set eagerly, which restrict their applicability.

If successful, the stable values preview would become part of the standard edition of Java, although no specific version has been named. The impact of this proposal could be significant, enabling Java developers to create more efficient and scalable applications. As the Java ecosystem continues to evolve, innovations like stable values are crucial to maintaining the platform's relevance and competitiveness.

The stable values proposal marks an important step forward in optimizing Java application performance. As the Java community continues to weigh in on the proposal, one thing is clear: the potential benefits of stable values could have a lasting impact on the way Java applications are developed and deployed.