Java 21 New Features (LTS) – Top 10 You Must Know
Java 21, the latest long-term support (LTS) release from Oracle and the OpenJDK community, brings a wealth of new features and improvements that cater to modern development needs. Designed to improve developer efficiency, system performance, and coding elegance, Java 21 thoughtfully balances innovation with backward compatibility.
This blog highlights the Top 10 Features in Java 21, helping you stay updated and ready to take full advantage of its powerful tools. Whether you’re migrating from Java 17/11 or just looking to learn about what’s new, this guide covers all the essentials in-depth.
Table of Contents
- Virtual Threads (Project Loom)
- Pattern Matching for Switch (Finalized)
- Sequenced Collections
- Structured Concurrency (Preview)
- Record Patterns
- String Templates (Preview)
- Improvements to ZGC and G1 GC
- JDK 21 + Spring Boot 3 Compatibility
- Deprecated/Removed Features
- Migration from Java 17/11
- FAQs
1. Virtual Threads (Project Loom)
One of the headline features in Java 21 is the introduction of virtual threads, a crucial part of Project Loom. Virtual threads revolutionize concurrency in Java by offering lightweight, scalable threads that reduce resource overhead.
Key Benefits of Virtual Threads:
- High Scalability: Handle massive numbers of threads efficiently (e.g., millions of tasks).
- Simpler Code: Replace the complexity of thread pools with direct thread management.
- Optimized for I/O: Excellent for managing blocking I/O, such as database queries or HTTP calls.
Example:
public class VirtualThreadsExample {
public static void main(String[] args) {
var thread = Thread.ofVirtual().start(() -> {
System.out.println("Running in a virtual thread!");
});
thread.join();
}
}
This dramatically simplifies threading without requiring special configurations or thread pools.
2. Pattern Matching for Switch (Finalized)
Java 21 finalizes pattern matching for switch, making conditional logic cleaner and more powerful. By combining the switch statement with pattern matching, you can implement complex logic without verbose type checks.
Example:
public static String process(Object obj) {
return switch (obj) {
case String s -> "String with value " + s;
case Integer i -> "Integer with value " + i;
case null -> "Null value provided";
default -> "Unknown type";
};
}
Benefits:
- Cleaner and more expressive switch constructs.
- Eliminates
instanceofand explicit casting.
3. Sequenced Collections
Java 21 introduces sequenced collections, ensuring a consistent ordering of elements in commonly-used collection types. This update provides a uniform API for ordered operations across List, Set, and Map.
Example:
SequencedSet<String> names = SequencedCollection.of("Alice", "Bob", "Charlie");
names.addFirst("Zara");
System.out.println(names); // [Zara, Alice, Bob, Charlie]
Why it matters:
- Reduces the need for external libraries like Apache Commons.
- Improves consistency and readability across codebases.
4. Structured Concurrency (Preview)
Structured concurrency, part of Project Loom, is introduced as a preview feature in Java 21. This paradigm simplifies multi-threaded operations by grouping related tasks and ensuring they complete or fail as a unit.
Benefits:
- Streamlined task management.
- Automatic cancellation and shutdown of threads.
Example:
try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
scope.fork(() -> fetchData());
scope.fork(() -> processResults());
scope.join();
}
This makes concurrent task execution safer, more intuitive, and less error-prone.
5. Record Patterns
Record patterns extend pattern matching capabilities to Record types, improving destructuring. This enhancement, coupled with switch, simplifies processing structured data models.
Example:
record User(String name, int age) {}
static void displayUser(Object obj) {
if (obj instanceof User(String name, int age)) {
System.out.println(name + " is " + age + " years old.");
}
}
Takeaway: You can now directly deconstruct objects inline, boosting code clarity.
6. String Templates (Preview)
Java 21 previews string templates, a feature designed to simplify concatenation and interpolation. Developers can construct dynamic strings safely and elegantly without messy concatenations or placeholders.
Example:
String name = "Alice";
String template = STR."Hello, \{name}!";
System.out.println(template); // "Hello, Alice!"
Why it’s game-changing: Safe, concise, and IDE-friendly, string templates eliminate common bugs in dynamic string construction.
7. Improvements to ZGC and G1 GC
Java 21 includes significant updates to two garbage collectors:
- ZGC (Z Garbage Collector): Reduced latency for ML and real-time applications.
- G1 GC (Garbage First GC): Enhanced throughput with better memory management algorithms.
Impact: These improvements ensure smoother performance for large-scale and latency-sensitive applications.
8. JDK 21 + Spring Boot 3 Compatibility
The alignment between JDK 21 and Spring Boot 3 LTS ensures full compatibility and synergy. Spring 6 (used in Spring Boot 3) is built to harness Java 21’s features like virtual threads, enabling developers to build even more efficient and responsive applications.
Benefits of the Pairing:
- Virtual thread support for Spring’s WebFlux.
- Performance gains for RESTful APIs and microservice applications.
9. Deprecated/Removed Features
Changes in Java 21 include several deprecated and removed APIs for better consistency and modernization.
Notable Changes:
- Deprecated
Thread.stop()method. - Removal of outdated
AppletAPI (finalized in Java 17).
Why it matters: These updates signify Java’s intent to simplify its ecosystem and eliminate legacy baggage.
10. Migration from Java 17/11
Migrating to Java 21 from prior LTS releases (17 or 11) offers immediate performance, productivity, and language enhancements.
Migration Steps:
- Dependency Update: Ensure all libraries (e.g., Spring, Hibernate) are compatible with Java 21.
- Feature Integration: Gradually adopt features like pattern matching and virtual threads.
- Testing: Use JUnit or TestNG to test feature compatibility across your application.
Tip: Tools like jdeprscan help identify deprecated APIs in your existing codebase.
FAQs
Is Java 21 worth upgrading to from Java 17?
Yes, Java 21 being an LTS release provides long-term stability, making it the best choice for enterprise adoption with the latest features.
What projects benefit most from virtual threads?
Applications with heavy concurrency, such as RESTful APIs, database interactions, or microservices, will see the greatest benefits.
Will Java 21 be backward compatible with Java 8 or older?
While Java 21 is backward compatible in most cases, older projects should review deprecated/removed features for smooth migration.
Summary
Java 21 takes a major step forward as an LTS release, equipping developers with enhanced concurrency, pattern matching, efficient collections, and streamlined syntax. Features like virtual threads, structured concurrency, and string templates stand out as significant upgrades that improve developer productivity and application performance.
To explore detailed documentation and start your migration, visit the official Java 21 Documentation. Upgrade today and future-proof your projects with the power of Java 21!
