Java 18 Features

Java 18 was released as a short-term release and focuses mainly on developer productivity, platform support, and incubator/preview improvements. While it doesn’t introduce as many headline language features as some other versions, it includes important upgrades you should know—especially if you’re maintaining modern Java applications.

1) Simple Web Server (JEP 408)

Java 18 introduces a minimal, built-in static file web server via the jwebserver tool. It’s great for:

  • Quickly serving static files
  • Testing HTML/JS builds locally
  • Lightweight demos without installing Node/Apache/etc.

✅ Example: Start a web server

# Serve current directory on port 8000
jwebserver

# Serve a specific directory
jwebserver --directory /path/to/site

# Choose another port
jwebserver --port 9090

What you get

  • Serves static files over HTTP
  • No servlet/JSP support (it’s intentionally simple)
  • Logs basic request info to console

Use case idea: Serve a dist/ folder from React/Angular build to quickly verify output.

2) UTF-8 by Default (JEP 400)

Before Java 18, the default charset could vary by OS and locale (e.g., Windows often used Cp1252). Java 18 makes UTF-8 the default charset on all platforms.

Why it matters

  • Fewer encoding bugs across environments
  • Consistent behavior in containers/servers/Windows/Linux
  • Better support for multilingual text

✅ Example: Check default charset

import java.nio.charset.Charset;

public class Utf8DefaultDemo {
    public static void main(String[] args) {
        System.out.println("Default charset: " + Charset.defaultCharset());
    }
}

✅ Example: Writing/Reading text becomes more predictable

import java.nio.file.Files;
import java.nio.file.Path;

public class FileCharsetDemo {
    public static void main(String[] args) throws Exception {
        Path p = Path.of("msg.txt");

        Files.writeString(p, "नमस्ते UTF-8 ✅"); // default charset is UTF-8 in Java 18+
        String text = Files.readString(p);

        System.out.println(text);
    }
}

Tip: For libraries and protocols, it’s still best practice to specify charset explicitly where required (e.g., HTTP headers).

3) Internet-Address Resolution SPI (JEP 418)

Java 18 adds a Service Provider Interface (SPI) to allow alternative implementations of hostname and address resolution.

Why it matters (practical scenarios)

  • Custom DNS resolution strategies
  • Better integration with containerized or service-mesh environments
  • Observability or policy-based resolution

Most developers won’t use this directly, but platform teams and infrastructure-heavy systems may benefit.

4) Code Snippets in JavaDoc (JEP 413)

Java 18 improves JavaDoc with a new @snippet tag that makes code examples cleaner and more maintainable than {@code ...} blocks.

✅ Example: JavaDoc snippet

/**
 * Parses input and returns a number.
 *
 * {@snippet :
 * int n = Integer.parseInt("123");
 * System.out.println(n);
 * }
 */
public class SnippetDocDemo {
}

Benefits

  • Cleaner docs for APIs
  • Easier to read than inline {@code}
  • Better formatting support

5) Pattern Matching for switch (Second Preview) (JEP 420)

Java 18 continues improving pattern matching in switch as a preview feature (not final yet in 18). It allows more expressive type checks and safer branching.

⚠️ Preview feature: must be enabled at compile/run time.

✅ Example: Pattern matching in switch (preview)

public class SwitchPatternDemo {
    static String format(Object obj) {
        return switch (obj) {
            case Integer i -> "int: " + i;
            case String s  -> "string: " + s;
            case null      -> "null value";
            default        -> "other: " + obj;
        };
    }

    public static void main(String[] args) {
        System.out.println(format(10));
        System.out.println(format("hello"));
        System.out.println(format(null));
    }
}

Compile & run (preview)

javac --release 18 --enable-preview SwitchPatternDemo.java
java --enable-preview SwitchPatternDemo

6) Vector API (Third Incubator) (JEP 417)

Java 18 ships the Vector API again as an incubator, helping write SIMD-style computations that the JVM can optimize for modern CPUs.

Where it’s useful

  • Image processing
  • Signal processing
  • Numeric computations
  • High-performance data pipelines

Most application developers won’t need it day-to-day, but it’s important for performance-focused libraries.

7) Foreign Function & Memory API (Second Incubator) (JEP 419)

This incubator API aims to improve calling native libraries (C/C++) and managing off-heap memory safely—an alternative path to JNI.

Why it matters

  • Safer and more ergonomic native access than JNI
  • Better performance options for systems programming and integration work

(As an incubator, it can change between releases.)

8) Deprecate Finalization for Removal (JEP 421)

Finalizers (protected void finalize()) are problematic: unpredictable timing, performance overhead, and security risks. Java 18 continues the move to deprecate finalization for removal.

✅ What to use instead

  • try-with-resources
  • AutoCloseable
  • Cleaner (when appropriate)

✅ Example: Prefer try-with-resources

import java.io.BufferedReader;
import java.io.FileReader;

public class ResourceDemo {
    public static void main(String[] args) throws Exception {
        try (BufferedReader br = new BufferedReader(new FileReader("data.txt"))) {
            System.out.println(br.readLine());
        }
    }
}

Java 18: Summary Table

  • jwebserver: quick static server
  • UTF-8 default: consistent encoding everywhere
  • JavaDoc @snippet: better documentation
  • switch pattern matching: improved expressiveness (preview)
  • Vector API / FFM API: performance + native integration (incubator)
  • Finalization deprecated: modern resource handling encouraged

Should You Upgrade to Java 18?

Java 18 is a short-term release. If you’re in production, teams usually prefer:

  • Java 17 (LTS) for stability
  • Or move to newer LTS versions when ready

But Java 18 is valuable if you want to:

  • Test preview features (like switch patterns)
  • Benefit from UTF-8 default consistency
  • Use jwebserver and JavaDoc snippets for tooling/productivity

FAQ

Is Java 18 an LTS release?

No. Java 18 is a short-term release.

Do I need to enable preview features?

Yes, for preview features like pattern matching for switch:

  • --enable-preview during compile and run

What’s the most impactful change for most developers?

UTF-8 by default and Simple Web Server are the most practical and immediately useful.