Although Java 21 has now taken center stage as the latest Long-Term Support (LTS) release, Java 17 remains widely used in enterprise environments. Released in September 2021, Java 17 is still a solid and stable choice for many organizations in 2025, thanks to its LTS support and the rich set of features it brought to the language and runtime.
Here’s a breakdown of the most impactful features and enhancements introduced in Java 17:
🔹 1. Sealed Classes (JEP 409)
Sealed classes offer a new way to control class hierarchies. By declaring which classes can extend or implement a class or interface, developers gain tighter control over inheritance and make code more predictable and secure.
Example:
java
public sealed class Shape permits Circle, Rectangle, Square {}
🔹 2. Pattern Matching for instanceof (JEP 394)
This feature simplifies type checks and casting. Instead of checking the type and then casting manually, Java 17 lets you do both in one line.
Before:
java
if (obj instanceof String) {
String s = (String) obj;
}
Now:
java
if (obj instanceof String s) {
// use s directly
}
🔹 3. Records (JEP 395)
Records are a concise way to declare immutable data classes without boilerplate code for constructors, getters, equals(), hashCode(), and toString().
Example:
java
public record Person(String name, int age) {}
🔹 4. New Garbage Collector: ZGC & Shenandoah
Java 17 enhances the Z Garbage Collector (ZGC) and Shenandoah, both low-latency GCs designed to handle large heaps with minimal pause times, making Java more suitable for real-time and high-throughput applications.
🔹 5. Foreign Function & Memory API (Incubator - JEP 412)
This API allows Java programs to call native code and access memory outside of the JVM safely and efficiently—without relying on JNI.
🔹 6. Enhanced Pseudorandom Number Generators (JEP 356)
Java 17 improves upon the existing random number generation capabilities by introducing new interfaces and implementations for flexible, stream-based RNGs.
🔹 7. Deprecations and Removals
Java 17 removed several outdated features:
- RMI Activation system
- Applet API
- Experimental AOT and JIT compiler
- Some root certificates
This helps clean up the JDK and reduce attack surfaces in security-sensitive environments.
🔹 8. JDK Flight Recorder (JFR) Event Streaming
With continuous streaming support, JFR allows better observability and performance diagnostics in real time.
🔹 9. Strong Encapsulation of JDK Internals
Java 17 strongly encapsulates internal JDK APIs, except for critical ones like sun.misc.Unsafe. This enforces modularity and discourages reliance on internal, unsupported APIs.
🔹 10. Platform Stability & Long-Term Support
As an LTS release, Java 17 offers long-term stability, security patches, and backporting of critical bug fixes until at least 2029—making it a safe and popular choice for enterprise-grade projects.
Conclusion:
Even with newer versions like Java 21 entering the spotlight, Java 17 is still very relevant in 2025. Its powerful blend of modern language features, performance enhancements, and long-term support make it an essential release in the Java ecosystem. Whether you're maintaining enterprise systems or building scalable cloud applications, understanding and leveraging Java 17 is a smart move.