- Understand the major language enhancements introduced between Java 8 and Java 21
- Apply pattern matching to eliminate verbose type checking and casting
- Implement record classes for immutable data modeling
- Utilize switch expressions for cleaner conditional logic
- Explore virtual threads for simplified concurrent programming
Java has undergone a remarkable transformation since Java 8's release in 2014. While that version introduced lambdas and streams—revolutionary at the time—the language has continued evolving with features that fundamentally change how we write code. Today's Java allows developers to express intent more clearly, reduce boilerplate significantly, and handle concurrency with unprecedented simplicity. This lesson explores the most impactful features from recent releases, particularly those available in Java 21 LTS, demonstrating how modern Java code differs dramatically from what many developers still write today. We'll focus on practical applications that intermediate Java developers can immediately apply to their existing codebases.
Traditional Java required verbose two-step type checking: first instanceof, then casting. Pattern matching combines both into one clean expression:
package academy.javapro;
public class PatternMatchingDemo {
static class Shape {
}
static class Circle extends Shape {
double radius = 5.0;
}
static class Square extends Shape {
double side = 4.0;
}
public static void main(String[] args) {
Shape shape = new Circle();
// Old way - tedious casting
if (shape instanceof Circle) {
Circle c = (Circle) shape;
System.out.println("Old: Circle radius " + c.radius);
}
// New way - pattern matching
if (shape instanceof Circle c) {
System.out.println("New: Circle radius " + c.radius);
}
}
}The pattern variable is scoped properly and eliminates redundant casts entirely.
Records eliminate boilerplate for data carriers. What once took 50+ lines now takes one:
package academy.javapro;
public class RecordDemo {
// One line gives you constructor, getters, equals, hashCode, toString!
record Person(String name, int age) {
}
public static void main(String[] args) {
Person john = new Person("John", 30);
Person jane = new Person("Jane", 28);
Person johnDupe = new Person("John", 30);
System.out.println(john); // Person[name=John, age=30]
System.out.println("Name: " + john.name()); // accessor method
System.out.println("Equal? " + john.equals(johnDupe)); // true - automatic equals
}
}Records are immutable by default, perfect for DTOs and value objects.
Switch becomes an expression that returns values, eliminating break statements and fall-through bugs:
package academy.javapro;
public class SwitchExpressionDemo {
enum Day {MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY}
public static void main(String[] args) {
Day today = Day.FRIDAY;
// Old switch - verbose
String oldType;
switch (today) {
case MONDAY:
case TUESDAY:
case WEDNESDAY:
case THURSDAY:
case FRIDAY:
oldType = "Weekday";
break;
default:
oldType = "Weekend";
}
// New switch expression - concise
String newType = switch (today) {
case MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY -> "Weekday";
case SATURDAY, SUNDAY -> "Weekend";
};
System.out.println("Today is a " + newType);
}
}Arrow syntax prevents fall-through and the compiler ensures exhaustiveness.
Virtual threads make concurrency trivial. No more complex thread pools:
package academy.javapro;
import java.util.concurrent.Executors;
public class VirtualThreadDemo {
public static void main(String[] args) throws Exception {
// Old way - managing thread pools
var oldExecutor = Executors.newFixedThreadPool(100);
// New way - virtual threads (can create millions!)
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
for (int i = 0; i < 5; i++) {
final int task = i;
executor.submit(() -> {
System.out.println("Task " + task + " on " + Thread.currentThread());
});
}
}
// Even simpler - direct virtual thread
Thread.startVirtualThread(() ->
System.out.println("Hello from virtual thread!")
).join();
}
}Virtual threads are lightweight—you can spawn millions without resource issues.
Here's how these features work together in real code:
package academy.javapro;
import java.util.List;
import java.util.concurrent.Executors;
public class ModernJavaCombo {
// Sealed class for finite types
sealed interface Response permits Success, Error {
}
record Success(String data) implements Response {
}
record Error(String message) implements Response {
}
static Response processRequest(String request) {
return request.isEmpty()
? new Error("Empty request")
: new Success("Processed: " + request);
}
public static void main(String[] args) throws Exception {
List<String> requests = List.of("Order-1", "Order-2", "", "Order-3");
// Process concurrently with virtual threads
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
var futures = requests.stream()
.map(req -> executor.submit(() -> processRequest(req)))
.toList();
// Pattern matching in switch
for (var future : futures) {
Response response = future.get();
String result = switch (response) {
case Success(var data) -> "✓ " + data;
case Error(var msg) -> "✗ " + msg;
};
System.out.println(result);
}
}
}
}This example shows records for data, sealed classes for exhaustive types, pattern matching for elegant handling, and virtual threads for simple concurrency.
No more string concatenation for multi-line text:
package academy.javapro;
public class TextBlockDemo {
public static void main(String[] args) {
// Old way - ugly concatenation
String oldJson = "{\n" +
" \"name\": \"John\",\n" +
" \"age\": 30\n" +
"}";
// New way - text blocks
String newJson = """
{
"name": "John",
"age": 30
}
""";
System.out.println(newJson);
}
}Text blocks preserve formatting and make code much more readable.
Modern Java has evolved far beyond its verbose reputation, offering features that rival newer languages while maintaining backward compatibility and the robustness of the JVM ecosystem. Pattern matching eliminates redundant casting, records remove boilerplate from data classes, switch expressions provide safer and more expressive conditional logic, and virtual threads revolutionize concurrent programming. These improvements aren't merely syntactic sugar—they represent fundamental enhancements to how Java developers model domains, handle data, and manage concurrency. Understanding and adopting these features transforms Java development from an exercise in boilerplate management to a productive, expressive programming experience.
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