In a move to enhance the safety and performance of Java applications, a JDK Enhancement Proposal (JEP) has been submitted to prepare the Java ecosystem for a future release that disallows mutation of final fields by default. The proposal, which was created in early February and updated on March 31, aims to enforce the immutability of final fields, making Java a more reliable and efficient platform.

The JEP proposes to issue warnings about uses of deep reflection to mutate final fields, preparing Java developers for a future release that restricts this capability by default. As of that release, developers will need to explicitly enable the mutation of final fields at startup. This change is expected to have a significant impact on the Java ecosystem, as it will ensure that final fields are truly immutable, enhancing the overall integrity of Java applications.

The motivation behind this proposal is rooted in the fact that Java developers rely heavily on final fields to represent immutable state. However, the current Java platform provides APIs that allow reassignment of final fields at any time, undermining the correctness and performance of Java applications. By enforcing the immutability of final fields, the proposal aims to restore trust in the value of these fields, enabling developers and the JVM to reason about correctness with confidence.

The proposal also highlights the importance of aligning final fields in normal classes with components of record classes, which cannot be mutated by deep reflection. Additionally, the plan ensures that serialization libraries can continue working with Serializable classes, even those with final fields, without any disruptions. Notably, there are no plans to deprecate or remove any part of the Java Platform API or prevent mutation of final fields by serialization libraries during deserialization.

The JEP does not specify a particular version of Java that will introduce the "final means final" capability, but it is clear that the Java community is moving towards a more secure and efficient platform. By restricting the mutation of final fields by default, Java developers can expect improved performance and reliability in their applications, making Java an even more attractive choice for building robust and scalable systems.

The implications of this proposal are far-reaching, and Java developers should start preparing for the changes ahead. By understanding the motivations behind this proposal and the benefits it brings, developers can take advantage of the enhanced safety and performance features in future Java releases. As the Java ecosystem continues to evolve, it is essential to stay informed about the latest developments and proposals that shape the future of Java.

In conclusion, the "final means final" proposal is a significant step towards enhancing the integrity and performance of Java applications. By enforcing the immutability of final fields, Java developers can build more reliable and efficient systems, and the Java ecosystem as a whole will benefit from improved safety and performance. As the Java community continues to move forward, it is essential to stay informed about the latest developments and proposals that shape the future of Java.