Exploring Java 18, Java 19, Java 20 and Java 21: Features, Use Cases, and Real-World Examples
- Sujeet Prajapati
- Aug 22
- 5 min read
Java continues to evolve at a rapid pace with its six-month release cycle, bringing incremental yet powerful improvements. While Java 8, 11, and 17 and 21 are long-term support (LTS) versions, non-LTS versions like Java 18, 19, and 20 act as stepping stones for innovation, giving developers a chance to explore new features early.
In this blog, we’ll walk through the key features of Java 18, 19, 20 and 21, their real-world use cases, and practical examples to help you understand why they matter.
Java 18 Features
1. Simple Web Server
Java 18 introduced a minimalistic HTTP web server for prototyping, testing, and educational purposes.
Use Case:Developers building quick REST APIs or testing endpoints without needing heavy frameworks like Spring Boot.
Example:
import com.sun.net.httpserver.HttpServer;
import java.io.OutputStream;
import java.net.InetSocketAddress;
public class SimpleServer {
public static void main(String[] args) throws Exception {
HttpServer server = HttpServer.create(new InetSocketAddress(8000), 0);
server.createContext("/hello", exchange -> {
String response = "Hello, Java 18!";
exchange.sendResponseHeaders(200, response.getBytes().length);
try (OutputStream os = exchange.getResponseBody()) {
os.write(response.getBytes());
}
});
server.start();
System.out.println("Server started on port 8000");
}
}
Example: Quickly setting up a mock backend for frontend teams without requiring full-fledged services.
2. UTF-8 by Default
Java 18 standardized UTF-8 as the default character set across platforms.
Use Case:Avoids encoding issues when processing files or sending API responses, ensuring consistent behavior in globalized applications.
3. Code Snippets in JavaDocs
JavaDocs now support @snippet, making documentation more developer-friendly.
Use Case:Helps enterprise teams document APIs with live code snippets for faster onboarding.
Java 19 Features
1. Virtual Threads (Preview - Project Loom)
Virtual threads are lightweight threads that simplify high-throughput concurrent applications.
Use Case:In FinTech or e-commerce platforms handling thousands of concurrent requests, virtual threads reduce complexity compared to reactive frameworks.
Example:
public class VirtualThreadDemo {
public static void main(String[] args) throws InterruptedException {
try (var executor = java.util.concurrent.Executors.newVirtualThreadPerTaskExecutor()) {
for (int i = 0; i < 1000; i++) {
executor.submit(() -> {
Thread.sleep(1000);
System.out.println("Executed by: " + Thread.currentThread());
return null;
});
}
}
}
}
2. Record Patterns (Preview)
Record patterns improve pattern matching for structured data.
Use Case:Parsing JSON or database records more efficiently.
Example:
record User(String name, int age) {}
public class RecordPatternDemo {
public static void main(String[] args) {
Object obj = new User("Alice", 28);
if (obj instanceof User(String name, int age)) {
System.out.println(name + " is " + age + " years old.");
}
}
}
3. Structured Concurrency (Incubator)
Simplifies managing concurrent tasks by treating multiple subtasks as a single unit of work.
Use Case:In microservices fetching data from multiple APIs, structured concurrency ensures clean error handling and cancellation.
Java 20 Features
1. Virtual Threads (Second Preview)
Refined version of virtual threads making them closer to GA (General Availability).
Real-World Impact:Scalable applications like chat systems, gaming servers, and financial platforms where thousands of connections must be handled simultaneously.
2. Record Patterns (Second Preview)
Extended support for record patterns to make destructuring even more powerful.
Example:
record Order(String id, double amount) {}
public class OrderProcessor {
public static void main(String[] args) {
Object obj = new Order("ORD123", 2500.50);
if (obj instanceof Order(String id, double amount)) {
System.out.println("Processing Order: " + id + " with Amount: " + amount);
}
}
}
3. Scoped Values (Incubator)
Scoped values provide a way to share immutable data across threads without using thread-local storage.
Use Case:In multi-threaded systems, pass context (like user session ID or request correlation ID) efficiently and safely.
Java 21 (LTS) – A Major Milestone
Java 21, released in September 2023, is a long-term support (LTS) release, making it the go-to version for enterprises planning upgrades. It consolidates innovations from Java 17 through 20 and introduces several powerful new features that redefine concurrency, data modeling, and code readability.
Key Features of Java 21
1. Virtual Threads (GA – Project Loom)
After years of previews, virtual threads are now production-ready in Java 21. They enable developers to write scalable concurrent applications with a familiar imperative style.
Use Case:In banking systems, handling thousands of transactions and API calls concurrently without complex reactive programming.
Example:
public class VirtualThreadApp {
public static void main(String[] args) throws Exception {
try (var executor = java.util.concurrent.Executors.newVirtualThreadPerTaskExecutor()) {
for (int i = 0; i < 10000; i++) {
executor.submit(() -> {
Thread.sleep(100);
System.out.println("Handled by: " + Thread.currentThread());
return null;
});
}
}
}
}
--> Handles 10,000+ concurrent tasks without blocking issues.
2. Record Patterns (GA)
Record patterns make pattern matching concise and expressive, especially for structured data.
Use Case:Parsing JSON payloads or working with domain objects in microservices.
Example:
record Customer(String name, int age, Address address) {}
record Address(String city, String country) {}
public class RecordPatternApp {
public static void main(String[] args) {
Customer customer = new Customer("Alice", 30, new Address("London", "UK"));
if (customer instanceof Customer(String name, int age, Address(String city, String country))) {
System.out.println(name + " from " + city + ", " + country);
}
}
}
3. Pattern Matching for Switch (GA)
This allows switch statements to match against types and conditions, making them more powerful and expressive.
Use Case:In e-commerce systems, classify different types of orders (digital, physical, subscription) with cleaner code.
Example:
public class SwitchPatternDemo {
static String orderType(Object obj) {
return switch (obj) {
case String s -> "Digital Order: " + s;
case Integer i -> "Physical Order ID: " + i;
case null -> "No Order Found";
default -> "Unknown Order Type";
};
}
public static void main(String[] args) {
System.out.println(orderType("E-Book"));
System.out.println(orderType(12345));
}
}
4. Sequenced Collections
A new SequencedCollection API was added to provide consistent handling of elements in order (first, last, reverse).
Use Case:In web applications, handling ordered data structures like browsing history or ordered logs.
Example:
import java.util.*;
public class SequencedCollectionDemo {
public static void main(String[] args) {
SequencedCollection<String> history = new ArrayList<>();
history.addFirst("Login");
history.addLast("View Profile");
history.addLast("Checkout");
System.out.println("First Action: " + history.getFirst());
System.out.println("Last Action: " + history.getLast());
System.out.println("Reverse Order: " + history.reversed());
}
}
5. String Templates (Preview – JEP 430)
String templates introduce interpolated strings, making dynamic string creation safer and cleaner.
Use Case:In logging systems or dynamic SQL queries, this reduces boilerplate and prevents errors.
Example:
import static java.lang.StringTemplate.STR;
public class StringTemplateDemo {
public static void main(String[] args) {
String name = "Alice";
int age = 30;
String message = STR."User \{name} is \{age} years old.";
System.out.println(message);
}
}
6. Scoped Values (Preview – JEP 429)
Scoped values allow thread-safe sharing of immutable data without using ThreadLocal.
Use Case:Pass request IDs or security tokens across async tasks in microservices.
7. Foreign Function & Memory API (Third Preview – Project Panama)
This API enables Java programs to call native libraries (C/C++) without JNI.
Use Case:In AI/ML applications, calling optimized C/C++ libraries for matrix operations.
Feature Comparison: Java 18 → Java 21
Feature | Java 18 | Java 19 | Java 20 | Java 21 (LTS) |
Simple Web Server | ✅ | ❌ | ❌ | ❌ |
UTF-8 Default Charset | ✅ | ✅ | ✅ | ✅ |
Virtual Threads (Loom) | ❌ | Preview | Preview | ✅ GA |
Record Patterns | ❌ | Preview | Preview | ✅ GA |
Pattern Matching for Switch | ❌ | Preview | Preview | ✅ GA |
Structured Concurrency | ❌ | Incubator | Incubator | ❌ (Deferred) |
Sequenced Collections | ❌ | ❌ | ❌ | ✅ |
String Templates | ❌ | ❌ | ❌ | Preview |
Scoped Values | ❌ | ❌ | Incubator | Preview |
Foreign Function & Memory API | ❌ | Preview | Preview | Preview |
Key Points
Java 18 – 20 introduced experimental features (simple web server, UTF-8, Loom, record patterns).
Java 21 (LTS) finalizes key features: Virtual Threads, Record Patterns, Pattern Matching for Switch, Sequenced Collections.
For enterprises, Java 21 is the recommended upgrade path since it’s an LTS version, combining innovation with long-term stability.
Java 21 empowers developers to build scalable, readable, and high-performance applications, making it the most exciting release since Java 8 and Java 17.
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