Java 17 features

This article describes the features which have been introduced in Java 17.

3/1/20244 min read

Java, a cornerstone of modern software development, has been evolving consistently over the years to meet the demands of the ever-changing technology landscape. With each release, new features and enhancements are introduced, empowering developers to write more efficient, secure, and maintainable code. Java 17, the latest long-term support (LTS) version, continues this tradition by offering a plethora of new features, improvements, and enhancements. In this comprehensive article, we delve into the key features of Java 17, exploring how they enhance developer productivity, code readability, and performance. From sealed classes to pattern matching, and from foreign function and memory API to enhanced garbage collection, Java 17 brings a wealth of new capabilities to the table, ensuring that Java remains at the forefront of software development.


Java has remained one of the most popular programming languages in the world for over two decades. With its strong ecosystem, platform independence, and robust performance, Java continues to power a wide range of applications, from enterprise systems to mobile apps and web services. Java's success lies not only in its initial design principles but also in its ability to adapt and evolve with the changing requirements of software development.

Java 17, released in September 2021, is the latest LTS version of the language. It follows the six-month release cadence established with Java 9, providing developers with a steady stream of new features and improvements. In this article, we explore the key features introduced in Java 17, analyzing their impact on developer workflows, code quality, and runtime performance.

Sealed Classes and Interfaces:

One of the most anticipated features in Java 17 is the introduction of sealed classes and interfaces. Sealed types provide a mechanism for restricting the inheritance hierarchy of classes and interfaces, allowing developers to define a finite set of subclasses or implementations.

By declaring a class or interface as sealed, developers can specify which classes or interfaces are permitted to extend or implement it. This enhances code maintainability and reduces the risk of unintended subclassing, leading to more robust and predictable codebases.

Sealed classes and interfaces are declared using the `sealed` modifier, followed by the permitted subclasses or implementations. For example:

public sealed class Shape

permits Circle, Rectangle, Triangle {

// Class definition



In this example, the `Shape` class is declared as sealed and permits the subclasses `Circle`, `Rectangle`, and `Triangle`. Any other attempt to subclass `Shape` would result in a compilation error.

Sealed classes and interfaces facilitate the creation of comprehensive type hierarchies, enabling developers to express their design intentions more clearly and concisely. They also lay the groundwork for future enhancements such as pattern matching and exhaustive switch statements.

Pattern Matching for switch:

Pattern matching is another significant addition to Java 17, building upon the switch statement introduced in Java 12. Pattern matching allows developers to perform deconstruction and conditional extraction of objects directly within the switch statement, eliminating the need for verbose instanceof checks and type casting.

With pattern matching for switch, developers can combine the benefits of switch statements with the expressive power of pattern matching, resulting in more concise and readable code. Consider the following example:

public static int calculateArea(Object obj) {

return switch (obj) {

case Circle c -> (int) (Math.PI c.getRadius() c.getRadius());

case Rectangle r -> r.getLength() * r.getWidth();

case Triangle t -> (int) (0.5 t.getBase() t.getHeight());

default -> throw new IllegalArgumentException("Unsupported shape: " + obj);



In this example, the switch statement uses pattern matching to match the input object to its corresponding shape type (Circle, Rectangle, or Triangle) and calculate the area accordingly. The `->` operator separates the pattern from the corresponding action, making the code more readable and maintainable.

Pattern matching for switch not only simplifies code but also improves type safety and reliability by reducing the likelihood of runtime errors caused by unchecked type casts.

Foreign Function and Memory API (Incubator):

Java 17 introduces the Foreign Function and Memory API as an incubator module, providing native interoperability capabilities to the Java platform. This API allows Java code to interact with native libraries and memory directly, opening up new possibilities for performance optimization and integration with native ecosystems.

The Foreign Function and Memory API enable developers to:

- Call native functions from Java code without using JNI (Java Native Interface).

- Access and manipulate native memory directly from Java code.

- Define and manipulate native data structures in Java code.

By providing a standardized mechanism for native interoperability, the Foreign Function and Memory API streamline the integration of Java applications with native libraries and systems, reducing the complexity and overhead associated with traditional JNI-based approaches.

Enhanced Garbage Collection:

Garbage collection (GC) is a critical aspect of Java's memory management model, responsible for reclaiming memory occupied by unreachable objects. With each release, Java's garbage collectors undergo enhancements and optimizations to improve performance, reduce latency, and minimize memory overhead.

In Java 17, several enhancements have been made to the garbage collectors, including:

- ZGC (Z Garbage Collector) enhancements for improved scalability and reduced latency.

- Shenandoah garbage collector improvements for reduced pause times and better scalability.

- G1 garbage collector enhancements for improved performance and reliability.

These enhancements make Java's garbage collectors more efficient and robust, allowing applications to achieve better overall performance and responsiveness, particularly in scenarios involving large heaps and high-throughput workloads.

Deprecation of Applet API:

Java 17 marks the deprecation of the Applet API, signaling the end of applets as a technology for deploying rich internet applications (RIAs) in web browsers. The Applet API, which was once a popular choice for web-based Java applications, has been superseded by modern web technologies such as HTML5, CSS, and JavaScript.

By deprecating the Applet API, Oracle encourages developers to migrate existing applet-based applications to alternative deployment solutions that leverage modern web standards and technologies. This aligns with the industry trend towards web-based applications and away from browser plugins and applets.


Java 17 brings a wealth of new features and enhancements to the Java platform, empowering developers to write more efficient, secure, and maintainable code. From sealed classes and pattern matching to native interoperability with the Foreign Function and Memory API, Java 17 offers a wide range of tools and capabilities for building modern applications.

By embracing these new features and best practices, developers can take full advantage of Java's strengths while adapting to the evolving demands of software development. Java's commitment to innovation and backward compatibility ensures that it remains a trusted and reliable choice for a wide range of applications, from enterprise systems to mobile apps and cloud services.

As Java continues to evolve, developers can look forward to further enhancements and improvements that will shape the future of the language and its ecosystem. With Java 17 as the latest milestone in its journey, Java reaffirms its position as a cornerstone of modern software development.