Java 18 to Java 20 introduced several enhancements focused on performance, developer productivity, and new language features. Let’s go through each version:

Java 18 Features (Released March 2022)

Java 18 was a relatively small update but introduced useful enhancements:

  1. UTF-8 as Default Charset
    • Java now defaults to UTF-8 for encoding text across different platforms.
    • Helps ensure consistency when handling text files globally.
  2. Simple Web Server
    • Introduced a built-in lightweight web server useful for development/testing: 
      jwebserver --port 8080
    • No need for third-party tools for basic testing.
  3. Code Snippets in Java API Documentation
    • Enhances Javadoc by allowing structured code snippets for better documentation.
  4. Vector API (Third Incubator)
    • Improved vector computation support, optimizing performance for mathematical operations.

Java 19 Features (Released September 2022)

Java 19 introduced preview and incubating features paving the way for future improvements:

  1. Virtual Threads (Preview)
    • Provides lightweight, high-performance threads for concurrent programming.
    • Significantly reduces thread management overhead: 
      try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
    executor.submit(() -> System.out.println("Hello from Virtual Thread!"));
}
  2. Structured Concurrency (Incubator)
    • Helps simplify multi-threaded applications with better lifecycle management.
  3. Foreign Function & Memory API (Second Incubator)
    • Allows Java to interact efficiently with native libraries without JNI.
  4. Pattern Matching for switch (Third Preview)
    • Enhances pattern matching by allowing type-based case handling.
  5. Linux-RISC-V Port
    • Introduces official support for the RISC-V architecture in Java.

Java 20 Features (Released March 2023)

Java 20 built upon Java 19’s preview features with refinements:

  1. Virtual Threads (Second Preview)
    • More improvements to make virtual threads production-ready.
  2. Scoped Values (Incubator)
    • Optimizes data sharing between threads without relying on thread-local storage.
  3. Structured Concurrency (Second Incubator)
    • Enhances parallel programming models, making multi-threading safer.
  4. Pattern Matching for switch (Fourth Preview)
    • Extends pattern matching capabilities with richer case handling.
  5. Foreign Function & Memory API (Third Incubator)
    • Brings it closer to becoming a standard feature in Java.

Java 18 to 20 focused on performance improvements, virtual threads, enhanced concurrency, and foreign memory interactions. Java is steadily evolving toward better parallel execution and native interoperability.