java-18.md

Java 18 Features

Released March 2022

1. UTF-8 by default JEP 400

This feature changes the default charset of the Java SE APIs to UTF-8. This means that the APIs that convert between bytes and strings will use UTF-8 as the default charset. This change is aimed at addressing the incompatibility between the default charset used by Java SE APIs and the charset used by many other APIs and libraries.

2. Simple Web Server JEP 408

This feature introduces a simple web server in the JDK. This web server is not intended for production use, but it can be very useful for prototyping, testing, and debugging. It supports HTTP/1.1 and HTTP/2, and it can serve static and generated content.

import com.sun.net.httpserver.HttpServer;
import com.sun.net.httpserver.HttpExchange;
import com.sun.net.httpserver.HttpHandler;

import java.io.OutputStream;
import java.io.IOException;
import java.net.InetSocketAddress;

public class SimpleWebServer {
    public static void main(String[] args) throws Exception {
        HttpServer server = HttpServer.create(new InetSocketAddress(8000), 0);
        server.createContext("/", new MyHandler());
        server.setExecutor(null); // creates a default executor
        server.start();
    }

    static class MyHandler implements HttpHandler {
        @Override
        public void handle(HttpExchange t) throws IOException {
            String response = "This is the response";
            t.sendResponseHeaders(200, response.length());
            OutputStream os = t.getResponseBody();
            os.write(response.getBytes());
            os.close();
        }
    }
}

3. Code Snippets in Java API Doc JEP 413

This feature enhances the Java API documentation with small examples of code, or code snippets, to illustrate the use of the API. This doesn't require a code example as it's a change in the documentation

4. Internet-Address Resolution SPI JEP 418

It introduces a service provider interface (SPI) by which alternate domain name and address resolution mechanisms can be used. This is more of a system-level change and doesn't have a straightforward code example.

5. Preview Features

5.1. Vector API JEP 417

This feature provides an initial iteration of an incubator module, jdk.incubator.vector, to express vector computations. Here's a basic example:

import jdk.incubator.vector.*;

public class VectorExample {
    public static void main(String[] args) {
        var a = Vector.of(1, 2, 3, 4);
        var b = Vector.of(2, 2, 2, 2);
        var c = a.mul(b);
        System.out.println(c);
    }
}

5.2. Foreign Function & Memory API (Second Incubator) JEP 419

An APIthat allows Java programs to safely and efficiently access foreign memory outside of the Java heap. Here's a basic example:

import jdk.incubator.foreign.*;

public class ForeignMemoryExample {
    public static void main(String[] args) {
        try (MemorySegment segment = MemorySegment.allocateNative(100)) { // Allocate 100 bytes of native memory
            MemoryAccess.setIntAtIndex(segment, 0, 123);  // Set the first 4 bytes to 123
            System.out.println(MemoryAccess.getIntAtIndex(segment, 0));  // Get the first 4 bytes
        }
    }
}

5.3. Pattern Matching for switch (second preview) JEP 420

public class PatternMatchingExample {
    public static void main(String[] args) {
        Object obj = "Hello, World!";
        switch (obj) {
            case Integer i -> System.out.println("Integer: " + i);
            case String s -> System.out.println("String: " + s);
            default -> System.out.println("Unknown type");
        }
    }
}