Java 17 Features Every Developer Should Know (With Code Examples)

🚀 Introduction

Java 17 is one of the most important releases in recent years because it is a Long-Term Support (LTS) version. This means that enterprises and developers can rely on it for years, making it an ideal upgrade from Java 11 or Java 8.

This article covers the top features in Java 17 that every developer should know, along with step-by-step examples to help you understand how to use them in real-world applications.

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🔹 1. Sealed Classes (Finalized in Java 17)

Sealed classes restrict which classes can extend them. This allows developers to have better control over their class hierarchies.

✅ Before (Java 16 – Preview Feature)

javaCopyEditpublic sealed class Vehicle permits Car, Bike { }
final class Car extends Vehicle { }
final class Bike extends Vehicle { }

• The sealed keyword ensures that only Car and Bike can extend Vehicle.

• Any other class trying to extend Vehicle will cause a compilation error.

✅ Now in Java 17 (Stable)

Sealed classes are now officially part of Java without requiring preview flags.

🔹 Real-World Use Case:
Sealed classes are useful for restricting inheritance in domain models.

javaCopyEditpublic sealed class Payment permits CreditCard, PayPal, Crypto { }
final class CreditCard extends Payment { }
final class PayPal extends Payment { }
final class Crypto extends Payment { }

✔ Helps with better maintainability
✔ Prevents unauthorized extensions

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🔹 2. Pattern Matching for switch (Preview)

Pattern Matching makes switch statements more powerful by allowing type checking directly within switch cases.

✅ Before (Old Java)

javaCopyEditObject obj = "Hello";
switch (obj) {
    case String s -> System.out.println(s.length());  // Not possible before Java 17
    default -> System.out.println("Not a string");
}

This wouldn't work in older Java versions because switch didn’t support types other than int, char, enum, or String.

✅ Now in Java 17

javaCopyEditObject obj = "Hashnode";
switch (obj) {
    case String s -> System.out.println("String length: " + s.length());
    case Integer i -> System.out.println("Integer value: " + i);
    default -> System.out.println("Unknown type");
}

✔ More readable code
✔ No need for instanceof checks
✔ Type safety built-in

🔹 Real-World Use Case:
Pattern Matching is useful in parsing JSON responses, where the object type is unknown.

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🔹 3. New Garbage Collector (ZGC & G1 Improvements)

Java 17 improves memory management with faster Garbage Collection (GC).

✅ What’s New?

• ZGC (Z Garbage Collector) now has lower latency

• G1 GC (Garbage-First) is faster in freeing unused memory

🔹 Performance Comparison:
🔸 Before (Java 11 G1 GC)

cssCopyEditAverage GC pause time: 100ms

🔸 Now (Java 17 ZGC)

cssCopyEditAverage GC pause time: 2ms 🚀

✔ Faster garbage collection = Better application performance
✔ Less memory footprint for high-load applications

🔹 Best Use Cases:
✔ Microservices running on Kubernetes
✔ Real-time processing applications

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🔹 4. Foreign Function & Memory API (Incubator)

Java 17 introduces better integration with native libraries like C++ or Rust.

✅ Before (Using JNI)

cCopyEditJNIEXPORT void JNICALL Java_MyClass_nativeMethod(JNIEnv *env, jobject obj) {
    printf("Hello from C!");
}

💡 JNI (Java Native Interface) was complex and slow.

✅ Now in Java 17 (Foreign API)

Java 17 introduces a better, safer, and faster way to call native code without JNI.

🔹 Real-World Use Case:
This is useful for calling OS-level functions or integrating with existing C++ libraries.

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🔹 5. Deprecated Security Features (TLS 1.0 & 1.1 Removed)

Java 17 improves security by removing outdated encryption protocols.

• TLS 1.0 and TLS 1.1 are completely removed.

• Only TLS 1.2 and TLS 1.3 are supported.

🔹 Real-World Impact:
If you run secure banking or fintech applications, you must update your TLS configurations.

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🔹 6. Strongly Encapsulated JDK Internals

🔒 Java 17 restricts access to internal APIs, improving security.

• Accessing internal JDK classes like sun.misc.Unsafe is now blocked by default.

• Use official APIs instead to avoid runtime errors.

🔹 Real-World Use Case:
If you're maintaining legacy applications, check for internal API dependencies to avoid failures.

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🔹 7. Improved Random Number Generators

Java 17 introduces new Random API methods for better randomness in java.util.random.

✅ New Random API

javaCopyEditRandomGenerator generator = RandomGenerator.of("L128X1024MixRandom");
System.out.println(generator.nextInt(100));

✔ More secure and predictable randomness
✔ Useful for AI, simulations, and cryptography

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🎯 Conclusion: Should You Upgrade to Java 17?

🔥 Yes! Java 17 brings huge improvements in performance, security, and developer experience.

✅ Key Benefits:
✔ 🚀 Sealed classes for controlled inheritance
✔ 🎯 Pattern Matching for switch = cleaner code
✔ 💾 ZGC improvements = better performance
✔ 🔐 More security features
✔ 📈 New APIs for randomness & memory

If you're working on microservices, finance, or cloud applications, upgrading to Java 17 is a must!