Java completed its 25 years in 2020. Ever since the programming language stepped into the market, it’s popularity only grew higher. Many features and enhancements have been made over the years that help boost the performance, stability, and security of the platform. The latest addition in the language is the general availability of Java 15 for all developers and enterprises.

Java Development Kit (JDK) 15, a follow-up release of JDK 14 which was released on 17th March 2020,  got a production release on 15th September 2020. It’s a short-term release with Oracle’s six-month support and will be followed by JDK 16 in March 2021. The upcoming long-term release would be JDK 17 having eight-year support, expected to take place in September 2021, according to Oracle’s six-month release cadence for Java SE versions. Developers can check out JDK 15 to get an idea of what JDK 17 will be like.

What’s new in Java 15?

Java 15 comes up with 14 major enhancements that include 1 incubator module, 2 deprecated features, 2 removals, and 3 preview features. The main highlights of JDK 15 encompass foreign-memory access API, hidden classes, Z Garbage collector, text blocks, and a preview of sealed classes, records, and pattern matching. Let’s understand the main JDK 15 features and changes briefly.

1. Foreign-Memory Access API

The Foreign-Memory Access API was originally put forward by JEP 370 and targeted to JDK 14. JEP 383 brings the feature back by re-incubating the API in JDK 15 and offers to incorporate feedback-based refinements. The incubating feature would help create an API that would let Java programs access foreign memory outside of the Java heap securely and efficiently. The API is expected to operate on different types of foreign memory, such as native, persistent, and managed heap. Several Java programs access foreign memory, such as MapDB and Ignite. The API would prove helpful to evade the cost and the unpredictability factor linked with garbage collection, share the memory with different processes, and serialize and deserialize memory content by mapping files into memory. At present, the Java API does not offer an adequate solution to access foreign memory. But with the second round of incubation, the API won’t be able to weaken the safety of Java Virtual Machine (JVM).

2. Hidden Classes

Hidden classes assist frameworks that need to generate classes at run time. These classes are beneficial because there is only one way to access them, i.e via reflection. They cannot be accessed directly from ordinary bytecode or bytecode of other classes. Frameworks generate classes to extend their behavior dynamically but it is advisable to limit access to those classes. Additionally, hidden classes may help minimize a framework’s memory’s footprint as they can be unloaded independently of other classes. To bring hidden classes to Java 15 would enhance the efficiency of entire languages on the Java Virtual Machine by entitling a standard API to such classes that are undiscoverable and possess a limited life cycle.

The objectives of this proposal involve-

1. Letting frameworks define classes as non-discoverable implementation details of the framework so that other classes can neither link against them nor discover them through reflection.
2. Support for aggressive unloading and expanding an access control nest on/with non-discoverable classes.
3. Deprecate the non-standard API: misc.Unsafe::defineAnonymousClass to deprecate for removal in a future release.

3. Z Garbage Collector and Shenandoah

Z Garbage Collector was introduced in JDK 11 as an experimental feature but has been turned into a production feature in Java 15. ZGC is a scalable low-latency garbage collector that was initially marked as experimental because the Java team thought a feature having such size and complexity should be introduced gradually and carefully. Ever since it arrived, several enhancements have been made such as concurrent class unloading, uncommitting of unused memory, support for class-data sharing, improved NUMA awareness, and multi-threaded heap pre-touching. The maximum heap size has also grown from 4 terabytes to 16 terabytes with a minimum at 8 MB. The most recent update has been the support for Windows and macOS platforms. ZGC tends to resolve performance issues in applications that comprise massive amounts of data, such as Machine Learning.

Like Z garbage collector, Shenandoah that was integrated into JDK 12 as an experimental feature is now ready as a production feature in JDK 15. Shenandoah minimizes the GC pause times by doing evacuation work and running Java threads simultaneously. With Shenandoah, pause times do not depend on the heap size which signifies that it would be uniform for every heap size.

4. Text Blocks

Text blocks first came into the picture in JDK 13 as a preview feature proposed by JEP 355, and later went on to receive the second preview through JEP 368 with two extra escape sequences in JDK 14. Text blocks are now ready to become a permanent and standard feature in JDK 15 as proposed by JEP 378.

A text block is a multi-line string literal that eliminates the need for most escape sequences, formats the string automatically in a predictable method, and provides developers with control over the format whenever they want. They tend to ease the task of writing Java programs. The text blocks proposal aims to improve the readability of strings in Java programs which indicate code written in non-Java languages and to support migration from string literals by specifying that any new construct can exhibit the same set of strings as a string literal, decipher the identical escape sequences and be controlled in the same manner as a string literal.

5. Preview of Sealed Classes and Records

This preview feature is intended to improve the productivity of developers by enhancing the Java programming language with sealed classes along with interfaces, that restrict which other classes or interfaces may extend or implement them. This provides the author of a class or interface with control over the codes responsible for implementing them, thereby offering a more elucidative way than access modifiers to limit the use of a superclass and support future directions in pattern matching by strengthening the exhaustive pattern analysis.

Records made their debut as a preview feature in JDK 14 and has been called in for a second preview/re-preview in JDK 15 to incorporate feedback-based improvements and to support additional forms of local classes and interfaces. Records also tend to enhance developer productivity by offering a compact syntax for classes that serve as transparent carriers for immutable data.
The above-mentioned five points have been the highlight of Java 15. The other enhancements/changes involve or revolve around Edwards-Curve Digital Signature Algorithm (EdSA), removal of Nashorn Javascript engine, removal of Solaris and SPARC ports, reimplementing the legacy DatagramSocket API, disabling and deprecating biased locking and RMI activation for removal. To get complete insights into JDK 15 features, visit the official guide here.