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Oracle has released version 20 of the Java programming language and virtual machine. The seven (7) JEPs in this final feature set include:

The feature cadence for Java 20 is similar to that of the seven (7) new features in JDK 19 and nine (9) new features in JDK 18. However, this is lower than some of the more recent pre-JDK 18 releases: 14 features in JDK 17; 17 features in JDK16; 14 features in JDK 15; and 16 features in JDK 14.

This release features JEPs that provide continued contribution toward Project Amber, Project Loom and Project Panama along with new rounds of preview and incubation. We examine a few of these new features here. It is worth noting that there were no JEPs representing Project Valhalla in JDK 20.

Project Panama

JEP 434 and JEP 438 fall under the auspices of Project Panama, a project designed to improve and enrich interoperability between the JVM and well-defined “foreign,” i.e., non-Java, APIs that will most-likely include interfaces commonly used within C libraries.

JEP 434, Foreign Function & Memory API (Second Preview), incorporate refinements based on feedback and to provide a second preview from JEP 424, Foreign Function & Memory API (Preview), delivered in JDK 19, and the related incubating JEP 419, Foreign Function & Memory API (Second Incubator), delivered in JDK 18; and JEP 412, Foreign Function & Memory API (Incubator), delivered in JDK 17. This feature provides an API for Java applications to interoperate with code and data outside of the Java runtime by efficiently invoking foreign functions and by safely accessing foreign memory that is not managed by the JVM. Updates from JEP 424 include: the MemorySegment and MemoryAddress interfaces are now unified, i.e., memory addresses are modeled by zero-length memory segments; and the sealed MemoryLayout interface has been enhanced to facilitate usage with JEP 427, Pattern Matching for switch (Third Preview), delivered in JDK 19.

JEP 438, Vector API (Fifth Incubator), incorporates enhancements in response to feedback from the previous four rounds of incubation: JEP 426, Vector API (Fourth Incubator), delivered in JDK 19; JEP 417, Vector API (Third Incubator), delivered in JDK 18; JEP 414, Vector API (Second Incubator), delivered in JDK 17; and JEP 338, Vector API (Incubator), delivered as an incubator module in JDK 16. This feature proposes to enhance the Vector API to load and store vectors to and from a MemorySegment as defined by JEP 424, Foreign Function & Memory API (Preview).

A working application on how to implement the Foreign Function & Memory API may be found in this GitHub repository by Carl Dea, senior developer advocate at Azul.

Project Loom

JEP 429, JEP 436 and JEP 437 fall under the auspices of Project Loom, a project designed to explore, incubate and deliver Java VM features and APIs built for the purpose of supporting easy-to-use, high-throughput lightweight concurrency and new programming models. This would be accomplished via virtual threads, delimited continuations and tail calls.

JEP 429, Scoped Values (Incubator), an incubating JEP formerly known as Extent-Local Variables (Incubator), proposes to enable sharing of immutable data within and across threads. This is preferred to thread-local variables, especially when using large numbers of virtual threads.

JEP 436, Virtual Threads (Second Preview), proposes a second preview from JEP 425, Virtual Threads (Preview), delivered in JDK 19, to allow time for additional feedback and experience for this feature to progress. This feature provides virtual threads, lightweight threads that dramatically reduce the effort of writing, maintaining, and observing high-throughput concurrent applications, to the Java platform. It is important to note that no changes are within this preview except for a small number of APIs from JEP 425 that were made permanent in JDK 19 and, therefore, not proposed in this second preview. More details on JEP 425 may be found in this InfoQ news story and this JEP Café screen cast by José Paumard, Java developer advocate, Java Platform Group at Oracle.

JEP 437, Structured Concurrency (Second Incubator), proposes to reincubate this feature from JEP 428, Structured Concurrency (Incubator), delivered in JDK 19, to allow time for additional feedback and experience. The intent of this feature is to simplify multithreaded programming by introducing a library to treat multiple tasks running in different threads as a single unit of work. This can streamline error handling and cancellation, improve reliability, and enhance observability. The only change is an updated StructuredTaskScope class to support the inheritance of scoped values by threads created in a task scope. This streamlines the sharing of immutable data across threads. Further details on JEP 428 may be found in this InfoQ news story.

Working applications on how to implement the Virtual Threads and Structured Concurrency APIs may be found in: this GitHub repository by Nicolai Parlog, Java developer advocate at Oracle; and this GitHub repository by Bazlur Rahman, Senior Software Engineer at Contrast Security.

Project Amber

JEP 432 and JEP 433 fall under the auspices of Project Amber, a project designed to explore and incubate smaller Java language features to improve productivity.

JEP 432, Record Patterns (Second Preview), incorporates enhancements in response to feedback from the previous round of preview, JEP 405, Record Patterns (Preview). This proposes to enhance the language with record patterns to deconstruct record values. Record patterns may be used in conjunction with type patterns to “enable a powerful, declarative, and composable form of data navigation and processing.” Type patterns were recently extended for use in switch case labels via: JEP 427, Pattern Matching for switch (Third Preview), delivered in JDK 19; JEP 420, Pattern Matching for switch (Second Preview), delivered in JDK 18; and JEP 406, Pattern Matching for switch (Preview), delivered in JDK 17. Changes from JEP 405 include: added support for inference of type arguments of generic record patterns; added support for record patterns to appear in the header of an enhanced for statement; and remove support for named record patterns.

Similarly, JEP 433, Pattern Matching for switch (Fourth Preview), incorporates enhancements in response to feedback from the previous three rounds of preview: JEP 427, Pattern Matching for switch (Third Preview), delivered in JDK 19; JEP 420, Pattern Matching for switch (Second Preview), delivered in JDK 18; and JEP 406, Pattern Matching for switch (Preview), delivered in JDK 17. Changes from JEP 427 include: a simplified grammar for switch labels; and inference of type arguments for generic type patterns and record patterns is now supported in switch expressions and statements along with the other constructs that support patterns.

A working application on how to implement the Record Patterns and Pattern Matching for switch APIs may be found in this GitHub repository, java-19 folder, by Wesley Egberto, Java technical lead at Global Points.

JDK 21

Only one (1) JEP has been Targeted for inclusion in JDK 21 at this time. JEP 431, Sequenced Collections, has been promoted from Proposed to Target to Targeted status for JDK 21. This JEP proposes to introduce “a new family of interfaces that represent the concept of a collection whose elements are arranged in a well-defined sequence or ordering, as a structural property of the collection.” Motivation was due to a lack of a well-defined ordering and uniform set of operations within the Collections Framework. Further details on JEP 431 may be found in this InfoQ news story.

However, based on recently submitted JEP drafts and JEP candidates that propose finalized features, we have surmised which JEPs have the potential to be included in JDK 21.

JEP 440, Record Patterns, has been promoted from its JEP Draft 8300541 to Candidate status this past week. This JEP finalizes this feature and incorporates enhancements in response to feedback from the previous two rounds of preview: JEP 432, Record Patterns (Second Preview), delivered in JDK 20; and JEP 405, Record Patterns (Preview), delivered in JDK 19. This feature enhances the language with record patterns to deconstruct record values. Record patterns may be used in conjunction with type patterns to “enable a powerful, declarative, and composable form of data navigation and processing.” Type patterns were recently extended for use in switch case labels via: JEP 420, Pattern Matching for switch (Second Preview), delivered in JDK 18, and JEP 406, Pattern Matching for switch (Preview), delivered in JDK 17. The most significant change from JEP 432 removed support for record patterns appearing in the header of an enhanced for statement.

Similarly, JEP 441: Pattern Matching for switch, has been promoted from its JEP Draft 8300542 to Candidate status. This JEP also finalizes this feature and incorporates enhancements in response to feedback from the previous four rounds of preview: JEP 433, Pattern Matching for switch (Fourth Preview), delivered in JDK 20; JEP 427, Pattern Matching for switch (Third Preview), delivered in JDK 19; JEP 420, Pattern Matching for switch (Second Preview), delivered in JDK 18; and JEP 406, Pattern Matching for switch (Preview), delivered in JDK 17. This feature enhances the language with pattern matching for switch expressions and statements.

JEP 442, Foreign Function & Memory API (Third Preview), has been promoted from its JEP Draft 8301625 to Candidate status. This JEP incorporate refinements based on feedback and to provide a third preview from: JEP 434, Foreign Function & Memory API (Second Preview), delivered in JDK 20; JEP 424, Foreign Function & Memory API (Preview), delivered in JDK 19, and the related incubating JEP 419, Foreign Function & Memory API (Second Incubator), delivered in JDK 18; and JEP 412, Foreign Function & Memory API (Incubator), delivered in JDK 17. This feature provides an API for Java applications to interoperate with code and data outside of the Java runtime by efficiently invoking foreign functions and by safely accessing foreign memory that is not managed by the JVM. Updates from JEP 434 include: centralizing the management of the lifetimes of native segments in the Arena interface; enhanced layout paths with a new element to dereference address layouts; and removal of the VaList class.

JEP Draft 8303683, Virtual Threads, was submitted by Ron Pressler, architect and technical lead for Project Loom at Oracle, and Alan Bateman, architect, Java Platform Group, at Oracle this past week. This JEP proposed to finalize this feature based on feedback from the previous two rounds of preview: JEP 436, Virtual Threads (Second Preview), delivered in JDK 20; and JEP 425, Virtual Threads (Preview), delivered in JDK 19. This feature provides virtual threads, lightweight threads that dramatically reduce the effort of writing, maintaining, and observing high-throughput concurrent applications, to the Java platform. The most significant change from JEP 436 is that virtual threads now fully support thread-local variables by eliminating the option to opt-out of using these variables. Further details on JEP 425 may be found in this InfoQ news story and this JEP Café screen cast by José Paumard, Java developer advocate, Java Platform Group at Oracle.

The formal release date for JDK 21 has not yet been announced, but it is expected to be delivered in mid-September 2023 as per the six-month release cadence. Developers can anticipate a feature freeze in mid-June 2023. More details on additional JEP drafts and candidates may be found in this more detailed InfoQ news story.

JDK 20 may now be downloaded from Oracle with binaries from other vendors expected to become available in the coming days.