JDK 26: The new features in Java 26

Abstract

Goals of this feature include allowing all garbage collectors to work smoothly with the AOT (ahead of time) cache introduced by Project Leyden, separating AOT cache from GC implementation details, and ensuring that use of the AOT cache does not materially impact startup time, relative to previous releases. The structured concurrency API simplifies concurrent programming by treating groups of related tasks running in different threads as single units of work, thereby streamlining error handling and cancellation, improving reliability, and enhancing observability. The G1 GC proposal notes that although G1, which is the default garbage collector of the HotSpot JVM, is designed to balance latency and throughput, achieving this balance sometimes impacts application performance adversely compared to throughput-oriented garbage collectors such as the Parallel and Serial collectors:

Java Development Kit (JDK) 26, a planned update to standard Java due March 17, 2026, has gathered nine features so far. The latest slated for the release include ahead-of-time object caching, an eleventh incubation of the Vector API, second previews of lazy constants and cryptographic objects encodings, a sixth preview of structured concurrency, and warnings about uses of deep reflection to mutate final fields.

While none of these features is yet listed on the OpenJDK page for JDK 26, all have been targeted for JDK 26 in their official JDK Enhancement Proposals (JEPs). The three features previously slated for JDK 26 include improving throughput by reducing synchronization in the G1 garbage collector (GC), HTTP/3 for the Client API, and removal of the Java Applet API.

A short-term release of Java backed by six months of Premier-level support, JDK 26 follows the September 16 release of JDK 25, which is a Long-Term Support (LTS) release backed by several years of Premier-level support.

With ahead-of-time object caching, the HotSpot JVM would gain improved startup and warmup times, so it can be used with any garbage collector including the low-latency Z Garbage Collector (ZGC). This would be done by making it possible to load cached Java objects sequentially into memory from a neutral, GC-agnostic format, rather than mapping them directly into memory in a GC-specific format. Goals of this feature include allowing all garbage collectors to work smoothly with the AOT (ahead of time) cache introduced by Project Leyden, separating AOT cache from GC implementation details, and ensuring that use of the AOT cache does not materially impact startup time, relative to previous releases.

The eleventh incubation of the Vector API introduces an API to express vector computations that reliably compile at run time to optimal vector instructions on supported CPUs. This achieves performance superior to equivalent scalar computations. The incubating Vector API dates back to JDK 16, which arrived in March 2021. The API is intended to be clear and concise, to be platform-agnostic, to have reliable compilation and performance on x64 and AArch64 CPUs, and to offer graceful degradation. The long-term goal of the Vector API is to leverage Project Valhalla enhancements to the Java object model.

Also on the docket for JDK 26 is another preview of an API for lazy constants, which had been previewed in JDK 25 via a stable values capability. Lazy constants are objects that hold unmodifiable data and are treated as true constants by the JVM, enabling the same performance optimizations enabled by declaring a field final. Lazy constants offer greater flexibility as to the timing of initialization.

The second preview of PEM (privacy-enhanced mail) encodings calls for an API for encoding objects that represent cryptographic keys, certificates, and certificate revocation lists into the PEM transport format, and for decoding from that format back into objects. The PEM API was proposed as a preview feature in JDK 25. The second preview features a number of changes, such as the PEMRecordclass is now named PEM and now includes a decode()method that returns the decoded Base64 content. Also, the encryptKey methods of the EncryptedPrivateKeyInfo class now are named encrypt and now accept DEREncodable objects rather than PrivateKeyobjects, enabling the encryption of KeyPair and PKCS8EncodedKeySpec objects.

The structured concurrency API simplifies concurrent programming by treating groups of related tasks running in different threads as single units of work, thereby streamlining error handling and cancellation, improving reliability, and enhancing observability. Goals include promoting a style of concurrent programming that can eliminate common risks arising from cancellation and shutdown, such as thread leaks and cancellation delays, and improving the observability of concurrent code.

New warnings about uses of deep reflection to mutate final fields are intended to prepare developers for a future release that ensures integrity by default by restricting final field mutation, in other words making final mean final, which will make Java programs safer and potentially faster. Application developers can avoid both current warnings and future restrictions by selectively enabling the ability to mutate final fields where essential.

The G1 GC proposal is intended to improve application throughput and latency when using the G1 garbage collector by reducing the amount of synchronization required between application threads and GC threads. Goals include reducing the G1 garbage collector’s synchronization overhead, reducing the size of the injected code for G1’s write barriers, and maintaining the overall architecture of G1, with no changes to user interaction.

The G1 GC proposal notes that although G1, which is the default garbage collector of the HotSpot JVM, is designed to balance latency and throughput, achieving this balance sometimes impacts application performance adversely compared to throughput-oriented garbage collectors such as the Parallel and Serial collectors:

Relative to Parallel, G1 performs more of its work concurrently with the application, reducing the duration of GC pauses and thus improving latency. Unavoidably, this means that application threads must share the CPU with GC threads, and coordinate with them. This synchronization both lowers throughput and increases latency.

A short-term release of Java backed by six months of Premier-level support, JDK 26 will follow the September 16 release of JDK 25, which is a Long-Term Support (LTS) release backed by several years of Premier-level support.

The HTTP/3 proposal calls for allowing Java libraries and applications to interact with HTTP/3 servers with minimal code changes. Goals include updating the HTTP Client API to send and receive HTTP/3 requests and responses; requiring only minor changes to the HTTP Client API and Java application code; and allowing developers to opt in to HTTP/3 as opposed to changing the default protocol version from HTTP/2 to HTTP/3.

HTTP/3 is considered a major version of the HTTP (Hypertext Transfer Protocol) data communications protocol for the web. Version 3 was built on the IETF QUIC (Quick UDP Internet Connections) transport protocol, which emphasizes flow-controlled streams, low-latency connection establishment, network path migration, and security among its capabilities.

Removal of the Java Applet API, now considered obsolete, is also targeted for JDK 26. The Applet API was deprecated for removal in JDK 17 in 2021. The API is obsolete because neither recent JDK releases nor current web browsers support applets, according to the proposal. There is no reason to keep the unused and unusable API, the proposal states.

Other possible features for JDK 26 include primitive types in patterns, instanceof, and switch, which was previewed in JDK 25. An experimental feature in JDK 25, JDK Flight Recorder CPU-time profiling, could also be included in JDK 26. A third possibility is post-mortem crash analysis with jcmd, which would extend the jcmd tool so that it could be used to diagnose a JVM that has crashed.