Java 21 Online Compiler — Run Java 21 Programs Free
Try the latest Java 21 (LTS) features directly in your browser with our free online compiler. Explore Virtual Threads (Project Loom), Record Patterns, Pattern Matching for switch, Sequenced Collections, and String Templates. No installation or setup required — start coding with Java 21 instantly.
Java 21 Features to Try
Virtual Threads
Create millions of lightweight threads with minimal overhead. Simplify concurrent programming without thread pools.
Record Patterns
Deconstruct record values directly in pattern matching. Extract components in a single, readable step.
Pattern Matching for switch
Use type patterns and guarded patterns in switch expressions. More powerful and readable control flow.
Sequenced Collections
New interfaces SequencedCollection, SequencedSet, SequencedMap with defined encounter order and reversed views.
String Templates (Preview)
Embed expressions directly in strings with STR."Hello \{name}" — type-safe string interpolation.
Unnamed Patterns
Use _ as a placeholder for unused variables in patterns and catches. Reduces noise in your code.
Frequently Asked Questions
What are the key features of Java 21?
Java 21 introduces Virtual Threads (Project Loom), Record Patterns, Pattern Matching for switch, String Templates (Preview), Sequenced Collections, and Unnamed Patterns. It is the latest LTS release.
What are Virtual Threads in Java 21?
Virtual Threads are lightweight threads managed by the JVM instead of the OS. You can create millions of virtual threads with minimal overhead. Syntax: Thread.startVirtualThread(() -> task()). They dramatically simplify concurrent programming.
Is Java 21 the latest version?
Java 21 is the latest Long-Term Support (LTS) release, released in September 2023. It will receive updates and support until at least 2031.
Should I upgrade from Java 17 to Java 21?
If you need Virtual Threads, Pattern Matching for switch, or Sequenced Collections then yes. Otherwise Java 17 is still fully supported and stable for production.
Can I try Java 21 features in this compiler?
Yes! Select "Java 21" from the version dropdown to access all Java 21 features. Virtual Threads, Record Patterns, and more are fully supported.