Introduction to Java SE 21

Java SE 21, officially released on September 19, 2023, marks a significant advancement in the Java platform as the third Long-Term Support (LTS) release under Oracle’s six-month release cadence. This version is set to enjoy LTS until September 2031, ensuring sustained support and updates for enterprise and production environments.

Quick Facts about Java SE 21

  • Official Release Date: September 19, 2023
  • LTS Support End Date: September 2031
  • Download Link: Java SE 21 Installer (Ensure you agree to Oracle’s license terms before downloading.)

Key Highlights

  • Pattern Matching for switch case: Enhance code readability and maintainability by allowing sophisticated data queries and transformations directly in switch statements.
  • Virtual Threads: Simplify the development of concurrent applications by providing lightweight threads, making it easier to write and maintain high-throughput server applications.
  • Sequenced Collections: Introduce new collection interfaces that provide guaranteed encounter order, improving predictability and ease of use when processing collections.


  • This course focuses exclusively on Long-Term Support (LTS) versions and standardized features.
  • You will not encounter preview or incubator features, nor non-LTS versions.
  • Instead, you’ll see features once they’re officially standardised, and features from non-LTS versions will be included in the next LTS versions’ summary and deep dive.
  • This chapter assumes familiarity with the previous LTS version of Java (Java 17).
  • We will cover all new features from every version since Java 17, including those from Java 18 through Java 20, leading up to and including Java 21.