Highlights of new features between Java 18 and 21

All changes
Java 18
- Simple Web Server
Java 19
Java 20
Java 21 (LTS)

All changes

Before we start with the highlights: in case you want to learn more or have a complete view of all changes, just head to the Open JDK website.

Java 18

UTF-8 by default, code snippets allowed in Javadoc, a bundled http server and deprecation of finalizers (try-catch-finally) in favor of try with resources. Not very exciting.

Simple Web Server

$ jwebserver -p 9000

var server = SimpleFileServer.createFileServer(
    new InetSocketAddress(8080), 
    Path.of("/some/path"), 
    OutputLevel.VERBOSE);
server.start

Java 19

No real features introduced, mainly previews.

Java 20

No real features introduced, mainly previews (again).

Java 21 (LTS)

This is where stuff gets released - not a ton, but a few nice additions!

Sequenced collections

A new interface called SequencedCollection<E> that represents collections with a specific sequence of elements, for traversal in reverse order and similar.

Pattern matching for Records (JEP 440)

In the same way that instanceof type inference was introduced in Java 16, the same is now available for Records.

Pattern matching for switch (JEP 441)

You can now use a more compact switch syntax, add cases for nulls and even simple logic to select cases.

static String typing(Object obj) {
    return switch (obj) {
        case Integer i -> String.format("int %d", i);
        case Long l    -> String.format("long %d", l);
        case Double d  -> String.format("double %f", d);
        case String s  -> String.format("String %s", s);
        default        -> obj.toString();
    };
}

static void logic(String s) {
    switch (s) {
        case null         -> System.out.println("Oops");
        case "Foo", "Bar" -> System.out.println("Great");
        case String s when s.length() == 1 -> System.out.println("One");
        default           -> System.out.println("Ok");
    }
}

Virtual threads (JEP 444)

Lightweight threads (like goroutines etc.) in Java, to enable using a threading model that scales with web server requests and similar.

try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
    IntStream.range(0, 10_000).forEach(i -> {
        executor.submit(() -> {
            Thread.sleep(Duration.ofSeconds(1));
            return i;
        });
    });
}  // executor.close() is called implicitly, and waits

Key Encapsulation Mechanism (JEP 452)

For cryptographical purposes, securing symmetrical keys.

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