Java 17 is a major release of the Java programming language and platform. It was officially released in September 2021. Java 17 is noteworthy for being a Long-Term Support (LTS) release, which means it will receive extended support and updates, making it a stable choice for enterprise applications.

Here are some key features and improvements introduced in Java 17:

1. Sealed Classes: Java 17 enhanced the sealed classes and interfaces feature introduced in Java 15. Sealed classes restrict which other classes or interfaces can extend or implement them, providing better control over class hierarchies.

2. Pattern Matching for switch: Building on the pattern matching feature introduced as a preview in Java 16, Java 17 finalized pattern matching for switch expressions. This feature simplifies code and makes it more concise and readable.

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   int result = switch (day) { case "Monday", "Tuesday" -> 1; case "Wednesday", "Thursday" -> 2; case "Friday" -> 3; default -> throw new IllegalArgumentException("Invalid day"); };

3. Foreign Function and Memory API (Incubator): Java 17 introduced the Foreign Function and Memory API as an incubator feature. It allows Java code to interact with native libraries and memory directly, providing improved performance and integration with native code.

4. Strong Encapsulation of Internal APIs: Java 17 continued the effort to strengthen the encapsulation of internal APIs, making it more challenging for external code to access internal APIs, enhancing security and maintainability.

5. Deprecation of Applet API: The Applet API, which has become obsolete due to changes in web technologies, has been deprecated in Java 17.

6. New macOS Rendering Pipeline: On macOS, Java 17 introduced a new rendering pipeline called Metal, improving the performance and user experience of Java applications on macOS.

7. Default ThreadLocalRandom Generator: The default random number generator (ThreadLocalRandom) was improved for better performance and security.

8. Enhanced Logging: Java 17 introduced enhancements to the logging system, providing better control over logging configuration and behavior.

9. Updated JDK Flight Recorder (JFR): The JDK Flight Recorder tool received various updates and improvements, making it more useful for monitoring and profiling Java applications.

10. New API Features and Bug Fixes: Java 17 included numerous API enhancements, bug fixes, and performance improvements across the platform.