Java 18 is still six months away but is already taking shape, with four feature proposals anticipated for it so far, the latest being a third incubation of the vector API.
The OpenJDK page for Java Development Kit (JDK) 18 lists the vector API, code snippets, and the UTF-8 charset as proposed to target JDK 18, as of September 20. The JEP (JDK Enhancement Proposal) index of Java technologies also cites the record patterns and array patterns proposal as eyed for JDK 18, although it has not been officially targeted yet.
While JDK 17, published September 14, was long-term support (LTS) release that will receive at least eight years of support from Oracle, JDK 18, expected in March 2022, will be a short-term feature release that is supported for six months. Early-access builds of JDK 18 can be found for Linux, Windows, and macOS at java.net.
Specifics of the three JDK 18 proposals include:
- The vector API would be incubated for a third time in JDK 18, having previously been incubated in JDK 16 and JDK 17. This proposal would express vector computations that compile at run time to optimal vector instructions on supported CPU architectures, achieving performance superior to equivalent scalar computations. Vector operations express a degree of parallelization enabling more work to be done on a single CPU cycle, thus producing significant performance improvements. The platform-agnostic vector API aims to provide a way to write complex algorithms in Java, using the existing HotSpot auto-vectorizer but with a user model that makes vectorization more predictable. JDK 18 would also add support for the ARM Scalar Vector Extension platform and improve the performance of vector operations that accept masks on architectures that support masking in hardware.
- A preview of record patterns and array patterns, in which the Java language would be enhanced with record patterns, to deconstruct record values, and array patterns, to deconstruct array values. Record patterns, array patterns, and type patterns, which were featured in JDK 16, can be nested so as to significantly enhance the expressiveness and utility of pattern matching. The goals of the proposal include extending pattern matching to express more sophisticated, composable data queries, and not changing the syntax or semantics of type patterns.
- Specifying UTF-8 as the default charset of the standard Java APIs. UTF-8 is a variable-wide character encoding for electronic communication and is considered the web’s standard charset. The charset is a character encoding capable of encoding all characters on the web. Through this change, APIs that depend on the default charset will behave consistently across all implementations, operating systems, locales, and configurations. The proposal is not intended to define new Java-standard or JDK-specific APIs. Proponents of the proposal expect that applications in many environments will see no impact from Java’s choice of UTF-8, like MacOS, many Linux distributions, and many server applications already support UTF-8. However, there is risk in other environments, the most obvious being that applications depending on the default charset will behave incorrectly when processing data produced when the default charset was unspecified. Data corruption may silently occur. The main impact is expected to befall users of Windows systems in Asian locales and possibly some server environments in Asia and other locales.
- Code snippets in Java API documentation, involving the introduction of an @snippet tag for JavaDoc’s Standard Doclet, to simplify the inclusion of example source code in the API documentation. Among the goals of the plan is facilitating the validation of source code fragments by providing API access to those fragments. While correctness is the responsibility of the author, enhanced support in JavaDoc and related tools can make it easier to achieve. Other goals include enabling modern styling, such as syntax highlighting, as well as the automatic linkage of names to declarations, and enabling better IDE support for creating and editing snippets. The proposal notes that authors of API documentation often include fragments of source code in documentation comments.
Other potential features that could target JDK 18 include pattern matching for switch expressions and statements, which is being previewed in the JDK 17 release, and a foreign function and memory API, which is in an incubator stage in JDK 17.