There was a flurry of activity in the OpenJDK ecosystem during the week of October 21st, 2024, highlighting: JEPs that have been Targeted and Proposed to Target for JDK 24; and drafts that have been promoted to Candidate status. JEP 485, Stream Gatherers, is the fifth JEP confirmed for JDK 24. Four JEPs have been Proposed to Target and will be under review during the week of October 28, 2024.
Targeted
After its review had concluded, JEP 485, Stream Gatherers, has been promoted from Proposed to Target to Targeted for JDK 24. This JEP proposes to finalize this feature after two rounds of preview, namely: JEP 473: Stream Gatherers (Second Preview), delivered in JDK 23; and JEP 461, Stream Gatherers (Preview), delivered in JDK 22. This feature was designed to enhance the Stream API to support custom intermediate operations that will "allow stream pipelines to transform data in ways that are not easily achievable with the existing built-in intermediate operations." More details on this JEP may be found in the original design document and this InfoQ news story.
Proposed to Target
JEP 490, ZGC: Remove the Non-Generational Mode, has been promoted from Candidate to Proposed to Target for JDK 24. This JEP proposes to remove the non-generational mode of the Z Garbage Collector (ZGC). The generational mode is now the default as per JEP 474, ZGC: Generational Mode by Default, delivered in JDK 23. By removing the non-generational mode of ZGC, it eliminates the need to maintain two modes and improves development time of new features for the generational mode. The review is expected to conclude on October 29, 2024.
JEP 487, Scoped Values (Fourth Preview), has been promoted from Candidate to Proposed to Target for JDK 24. Formerly known as Extent-Local Variables (Incubator), proposes a fourth preview, with one change, in order to gain additional experience and feedback from one round of incubation and three rounds of preview, namely: JEP 481, Scoped Values (Third Preview), delivered in JDK 23; JEP 464, Scoped Values (Second Preview), delivered in JDK 22; JEP 446, Scoped Values (Preview), delivered in JDK 21; and JEP 429, Scoped Values (Incubator), delivered in JDK 20. This feature enables sharing of immutable data within and across threads. This is preferred to thread-local variables, especially when using large numbers of virtual threads. The only change from the previous preview is the removal of the callWhere() and runWhere() methods from the ScopedValue class that leaves the API fluent. The ability to use one or more bound scoped values is accomplished via the call() and run() methods defined in the ScopedValue.Carrier class. The review is expected to conclude on October 30, 2024.
JEP 478, Key Derivation Function API (Preview), has been promoted from Candidate to Proposed to Target for JDK 24. This JEP proposes to introduce an API for Key Derivation Functions (KDFs), cryptographic algorithms for deriving additional keys from a secret key and other data, with goals to: allow security providers to implement KDF algorithms in either Java or native code; and enable the use of KDFs in implementations of JEP 452, Key Encapsulation Mechanism. The review is expected to conclude on October 31, 2024.
JEP 404, Generational Shenandoah (Experimental), has been promoted from Candidate to Proposed to Target for JDK 24. Originally targeted for JDK 21, JEP 404 was officially removed from the final feature set due to the "risks identified during the review process and the lack of time available to perform the thorough review that such a large contribution of code requires." The Shenandoah team decided to "deliver the best Generational Shenandoah that they can" and target a future release. The review is expected to conclude on October 30, 2024.
New JEP Candidates
JEP 495, Simple Source Files and Instance Main Methods (Fourth Preview), has been promoted from its JEP Draft 8335984 to Candidate status. This JEP proposes a fourth preview without change (except for a second name change), after three previous rounds of preview, namely: JEP 477, Implicitly Declared Classes and Instance Main Methods (Third Preview), delivered in JDK 23; JEP 463, Implicitly Declared Classes and Instance Main Methods (Second Preview), delivered in JDK 22; and JEP 445, Unnamed Classes and Instance Main Methods (Preview), delivered in JDK 21. This feature aims to "evolve the Java language so that students can write their first programs without needing to understand language features designed for large programs." This JEP moves forward the September 2022 blog post, Paving the on-ramp, by Brian Goetz, Java language architect at Oracle. Gavin Bierman, consulting member of technical staff at Oracle, has published the first draft of the specification document for review by the Java community. More details on JEP 445 may be found in this InfoQ news story.
JEP 494, Module Import Declarations (Second Preview), has been promoted from its JEP Draft 8335987 to Candidate status.This JEP proposes a second preview after the first round of preview, namely: JEP 476, Module Import Declarations (Preview), delivered in JDK 23. This feature will enhance the Java programming language with the ability to succinctly import all of the packages exported by a module with a goal to simplify the reuse of modular libraries without requiring to import code to be in a module itself. Changes from the first preview include: remove the restriction that a module is not allowed to declare transitive dependencies on the java.base module; revise the declaration of the java.se module to transitively require the java.base module; and allow type-import-on-demand declarations to shadow module import declarations. These changes mean that importing the java.se module will import the entire Java SE API on demand.
JEP 493, Linking Run-Time Images without JMODs, has been promoted from its JEP Draft 8333799 to Candidate status. This JEP proposes to "reduce the size of the JDK by approximately 25% by enabling the jlink tool to create custom run-time images without using the JDK's JMOD files." This feature must explicitly be enabled upon building the JDK. Developers are now allowed to link a run-time image from their local modules regardless where those modules exist.
JDK 24 Release Schedule
The JDK 24 release schedule, as approved by Mark Reinhold, Chief Architect, Java Platform Group at Oracle, is as follows:
- Rampdown Phase One (fork from main line): December 5, 2024
- Rampdown Phase Two: January 16, 2025
- Initial Release Candidate: February 6, 2025
- Final Release Candidate: February 20, 2025
- General Availability: March 18, 2025
For JDK 24, developers are encouraged to report bugs via the Java Bug Database.