1.4 Overview Of JDK 25 Features

Java 25, released in September 2024, represents the evolution of the platform with finalized features from previous preview cycles and new preview capabilities. This chapter covers the key features you'll encounter in modern Java development and how they improve the developer experience.

Finalized Language Features

Pattern Matching (Complete)

Pattern matching, finalized in Java 21 and matured through Java 25, provides exhaustive, declarative matching:

Type Patterns with instanceof:

if (obj instanceof String s) {
    System.out.println("Length: " + s.length());
} else if (obj instanceof Integer i) {
    System.out.println("Value: " + i);
}

Record Patterns:

record Point(int x, int y) {}

if (value instanceof Point(int x, int y) && x > 0) {
    System.out.println("Quadrant I");
}

Switch Pattern Matching:

var result = switch (obj) {
    case String s -> "Text: " + s;
    case Integer i -> "Number: " + i;
    case Point(int x, int y) -> "Point at (" + x + ", " + y + ")";
    case null -> "Nothing";
    default -> "Unknown";
};

Records

Records (finalized in Java 16) are now ubiquitous in modern Java for immutable data transfer objects:

public record User(String id, String name, String email) {}

// Automatically generates constructor, getters, equals(), hashCode(), toString()
var user = new User("123", "Alice", "alice@example.com");
System.out.println(user.name()); // Alice

Text Blocks

Text blocks (finalized in Java 15) make multi-line strings readable:

String sql = """
    SELECT id, name, email
    FROM users
    WHERE active = true
    ORDER BY created_at DESC
    """;

String json = """
    {
        "status": "success",
        "data": [1, 2, 3]
    }
    """;

Virtual Threads (Stable)

Virtual threads (Project Loom), finalized in Java 21 and stable in Java 25, transform concurrent programming:

// Create millions of virtual threads efficiently
ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor();

for (int i = 0; i < 1_000_000; i++) {
    executor.submit(() -> {
        // Blocking I/O operations are efficient on virtual threads
        var response = httpClient.send(request);
        processResponse(response);
    });
}

Virtual threads are ideal for:

• Microservices handling many concurrent requests
• I/O-bound applications (HTTP clients, database queries)
• Replacing callback-based async code with simple sequential logic

Modern APIs

Java HTTP Client

The java.net.http client (finalized in Java 11, enhanced through Java 25) is the standard for HTTP:

HttpClient client = HttpClient.newBuilder()
    .version(HttpClient.Version.HTTP_2)
    .connectTimeout(Duration.ofSeconds(10))
    .build();

var request = HttpRequest.newBuilder()
    .GET()
    .uri(URI.create("https://api.example.com/users"))
    .build();

var response = client.send(request, HttpResponse.BodyHandlers.ofString());
System.out.println(response.body());

java.time

The java.time API (since Java 8, enhanced through Java 25) handles date/time correctly:

var now = LocalDateTime.now();
var tomorrow = now.plusDays(1);
var deadline = LocalDateTime.of(2025, Month.DECEMBER, 31, 23, 59, 59);

var duration = Duration.between(now, deadline);
var days = duration.toDays();

var formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
System.out.println(now.format(formatter));

Collections and Streams

Immutable collections (Java 9+) and declarative streams remain core to modern Java:

var names = List.of("Alice", "Bob", "Charlie");
var counts = Map.of("a", 1, "b", 2);
var tags = Set.of("java", "concurrency", "performance");

var result = users.stream()
    .filter(u -> u.active())
    .map(User::name)
    .sorted()
    .collect(Collectors.toList());

JVM Improvements

Garbage Collectors

Java 25 supports multiple modern garbage collectors optimized for different workloads:

• G1GC (default): Low latency, predictable pause times
• ZGC: Ultra-low latency (<10ms pauses) for large heaps
• Shenandoah: Concurrent garbage collection for predictable performance

# Start with ZGC for latency-sensitive applications
java -XX:+UseZGC -Xmx16g MyApplication

Java Flight Recorder (JFR)

JFR provides production-grade profiling without significant overhead:

# Record application with JFR
java -XX:StartFlightRecording=filename=profile.jfr MyApplication

# Analyze with JDK Mission Control
jcmd MyApplication JFR.dump filename=output.jfr

Sealed Classes

Sealed classes restrict inheritance hierarchies for safer polymorphism:

public sealed class Response permits SuccessResponse, ErrorResponse {}
public final class SuccessResponse extends Response {}
public final class ErrorResponse extends Response {}

// Switch is exhaustive—no default case needed
var message = switch (response) {
    case SuccessResponse r -> "Success: " + r.data();
    case ErrorResponse r -> "Error: " + r.error();
};

Preview Features in Java 25

Java 25 introduces preview features available with --enable-preview. These are experimental and subject to change:

• Unnamed Variables (simplifying pattern matching)
• Implicit Class Declarations (lightweight main for learning)
• Enhanced FFM API (Foreign Function & Memory for native code)

Preview features let you experiment early; avoid them in production until they finalize.

Conclusion

Java 25 represents a mature, modern platform with strong foundations in:

• Type Safety: Static typing with records and pattern matching
• Concurrency: Virtual threads for scalable blocking I/O
• Performance: Multiple GC options, JIT optimization, low-latency profiling
• Productivity: Records, text blocks, and pattern matching reduce boilerplate

The next chapter covers practical migration strategies when upgrading from earlier Java versions.