java-25.md

Java 25 Features (LTS)

Released on September 16, 2025.

• Java 25 is a Long-Term Support (LTS) release, continuing Java's evolution with a focus on simplicity and performance.
• It brings significant improvements in language expressiveness, performance, observability, and security.
• This version introduces features like Primitive Types in Patterns, Flexible Constructor Bodies, and Generational Shenandoah GC.

1. Primitive Types in Patterns JEP 507 (Preview)

• Primitive Types in Patterns allow pattern matching with primitive types (int, double, long, etc.) in instanceof and switch.
• This feature removes previous restrictions and makes code cleaner when mixing primitives and reference types.
• Note: This is a preview feature in Java 25, use --enable-preview flag.

Before Java 25 (Traditional Approach)

public void processValue(Object obj) {
    if (obj instanceof Integer) {
        Integer boxed = (Integer) obj;
        int i = boxed;  // Unboxing needed
        System.out.println("Integer value: " + i);
    } else if (obj instanceof Double) {
        Double boxed = (Double) obj;
        double d = boxed;  // Unboxing needed
        System.out.println("Double value: " + d);
    }
}

With Java 25 (Primitive Pattern Matching)

public void processValue(Object obj) {
    if (obj instanceof int i) {  // Direct primitive pattern
        System.out.println("Integer value: " + i);
    } else if (obj instanceof double d) {  // Direct primitive pattern
        System.out.println("Double value: " + d);
    } else if (obj instanceof long l) {
        System.out.println("Long value: " + l);
    }
}

Primitive Patterns in Switch

public String describeNumber(Object obj) {
    return switch (obj) {
        case int i when i > 0 -> "Positive integer: " + i;
        case int i when i < 0 -> "Negative integer: " + i;
        case int i -> "Zero";
        case double d when d > 0.0 -> "Positive double: " + d;
        case double d -> "Non-positive double: " + d;
        case long l -> "Long value: " + l;
        default -> "Not a number type";
    };
}

// Usage
System.out.println(describeNumber(42));        // Positive integer: 42
System.out.println(describeNumber(-5));        // Negative integer: -5
System.out.println(describeNumber(3.14));      // Positive double: 3.14
System.out.println(describeNumber(100L));      // Long value: 100

Real-World Example: Processing Mixed Data

public class DataProcessor {
    public void processData(List<Object> data) {
        for (Object item : data) {
            switch (item) {
                case int i when i > 1000 -> 
                    System.out.println("Large number: " + i);
                case int i -> 
                    System.out.println("Small number: " + i);
                case double d -> 
                    System.out.printf("Decimal: %.2f%n", d);
                case String s -> 
                    System.out.println("Text: " + s);
                case null -> 
                    System.out.println("Null value");
                default -> 
                    System.out.println("Unknown type");
            }
        }
    }
}

// Usage
List<Object> data = List.of(42, 3.14, "Hello", 2000, null, 999);
new DataProcessor().processData(data);

2. Module Import Declarations JEP 511

• Module Import Declarations introduce import module <module-name> syntax for cleaner module usage.
• Simplifies code that uses Java Platform Module System (JPMS).
• Makes it easier to work with modular applications.

Traditional Module Usage

import java.util.List;
import java.util.ArrayList;
import java.util.Map;
import java.util.HashMap;
import java.util.stream.Collectors;
import java.util.stream.Stream;
// ... many more imports

public class MyApp {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();
        // ...
    }
}

With Module Import (Java 25)

import module java.base;  // Import entire module

public class MyApp {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();
        Map<String, Integer> scores = new HashMap<>();
        // All java.base classes are available
    }
}

Custom Module Import

// In your module-info.java
module com.mycompany.app {
    requires com.mycompany.utils;
    requires java.sql;
}

// In your source file
import module com.mycompany.utils;  // Import all exported packages

public class BusinessLogic {
    public void process() {
        // Use utility classes without individual imports
        StringUtils.capitalize("hello");
        DateUtils.formatNow();
    }
}

3. Flexible Constructor Bodies JEP 513

• Flexible Constructor Bodies allow statements before super() or this() calls in constructors.
• Enables validation and computation before delegating to another constructor.
• Reduces boilerplate and makes validation more natural.

Before Java 25 (Traditional)

public class User {
    private final String name;
    private final int age;
    
    public User(String name, int age) {
        // Can't validate before super()
        super();
        
        // Validation after super()
        if (name == null || name.isBlank()) {
            throw new IllegalArgumentException("Name cannot be empty");
        }
        if (age < 0 || age > 150) {
            throw new IllegalArgumentException("Invalid age");
        }
        
        this.name = name;
        this.age = age;
    }
}

With Java 25 (Flexible Constructor Bodies)

public class User {
    private final String name;
    private final int age;
    
    public User(String name, int age) {
        // Validation BEFORE super()!
        if (name == null || name.isBlank()) {
            throw new IllegalArgumentException("Name cannot be empty");
        }
        if (age < 0 || age > 150) {
            throw new IllegalArgumentException("Invalid age");
        }
        
        super();  // Now we can call super after validation
        
        this.name = name;
        this.age = age;
    }
}

Constructor Delegation with Pre-Processing

public class Rectangle {
    private final double width;
    private final double height;
    
    // Main constructor
    public Rectangle(double width, double height) {
        // Validate before super()
        if (width <= 0 || height <= 0) {
            throw new IllegalArgumentException("Dimensions must be positive");
        }
        super();
        this.width = width;
        this.height = height;
    }
    
    // Delegating constructor with computation before this()
    public Rectangle(double side) {
        // Compute and validate before delegating
        double normalizedSide = Math.abs(side);
        if (normalizedSide == 0) {
            normalizedSide = 1.0;  // Default value
        }
        
        this(normalizedSide, normalizedSide);  // Delegate after computation
    }
}

// Usage
Rectangle rect1 = new Rectangle(10);      // Creates 10x10 square
Rectangle rect2 = new Rectangle(-5);      // Creates 5x5 square (normalized)

Real-World Example: Entity with Complex Validation

public class BankAccount {
    private final String accountNumber;
    private final String ownerName;
    private final double initialBalance;
    
    public BankAccount(String accountNumber, String ownerName, double initialBalance) {
        // Complex validation before super()
        if (accountNumber == null || !accountNumber.matches("[0-9]{10}")) {
            throw new IllegalArgumentException("Invalid account number format");
        }
        
        String trimmedName = ownerName != null ? ownerName.trim() : "";
        if (trimmedName.length() < 2) {
            throw new IllegalArgumentException("Owner name too short");
        }
        
        if (initialBalance < 0) {
            throw new IllegalArgumentException("Initial balance cannot be negative");
        }
        
        super();
        
        this.accountNumber = accountNumber;
        this.ownerName = trimmedName;
        this.initialBalance = initialBalance;
    }
}

4. Instance Main Methods & Compact Source Files JEP 512

• Instance Main Methods allow main() to be an instance method instead of static.
• Compact Source Files reduce ceremony for simple programs - great for learning and scripting.
• Makes Java more beginner-friendly and reduces boilerplate.

Traditional Java Program

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Compact Source File (Java 25)

// No 'public', no 'static', no 'String[] args' required!
class Hello {
    void main() {
        System.out.println("Hello, Java 25!");
    }
}

Instance Main with Fields and Methods

class Calculator {
    private int result = 0;
    
    void main() {
        add(10);
        multiply(5);
        subtract(15);
        System.out.println("Final result: " + result);
    }
    
    void add(int value) {
        result += value;
        System.out.println("After add: " + result);
    }
    
    void multiply(int value) {
        result *= value;
        System.out.println("After multiply: " + result);
    }
    
    void subtract(int value) {
        result -= value;
        System.out.println("After subtract: " + result);
    }
}

Default Imports

// Many common packages are imported by default
class DataProcessor {
    void main() {
        // List, Map, etc. are automatically available
        List<String> names = List.of("Alice", "Bob", "Charlie");
        
        Map<String, Integer> ages = new HashMap<>();
        ages.put("Alice", 25);
        ages.put("Bob", 30);
        
        // Stream operations work too
        names.stream()
            .map(String::toUpperCase)
            .forEach(System.out::println);
    }
}

5. Scoped Values (Final) JEP 506

• Scoped Values provide immutable, shareable context across threads - finalized in Java 25.
• Better alternative to ThreadLocal for virtual threads and concurrent programming.
• Automatic cleanup and inheritance across thread boundaries.

ThreadLocal Problems

// Traditional ThreadLocal - manual cleanup needed
public class UserContext {
    private static final ThreadLocal<String> CURRENT_USER = new ThreadLocal<>();
    
    public static void setUser(String user) {
        CURRENT_USER.set(user);
    }
    
    public static String getUser() {
        return CURRENT_USER.get();
    }
    
    public static void clear() {
        CURRENT_USER.remove();  // Easy to forget!
    }
}

Scoped Values (Java 25)

public class UserContext {
    public static final ScopedValue<String> CURRENT_USER = ScopedValue.newInstance();
    
    public static void processRequest(String userId) {
        ScopedValue.where(CURRENT_USER, userId).run(() -> {
            // User ID is available in this scope
            handleRequest();
            
            // Automatically inherited by virtual threads!
            Thread.startVirtualThread(() -> {
                String user = CURRENT_USER.get();
                System.out.println("Processing for user: " + user);
            });
        });
        // Automatically cleaned up after scope
    }
    
    private static void handleRequest() {
        String user = CURRENT_USER.get();
        System.out.println("Handling request for: " + user);
    }
}

Real-World Example: Web Request Processing

public class WebRequestHandler {
    private static final ScopedValue<String> REQUEST_ID = ScopedValue.newInstance();
    private static final ScopedValue<String> USER_ID = ScopedValue.newInstance();
    private static final ScopedValue<String> TRACE_ID = ScopedValue.newInstance();
    
    public void handleRequest(String requestId, String userId, String traceId) {
        ScopedValue.where(REQUEST_ID, requestId)
                   .where(USER_ID, userId)
                   .where(TRACE_ID, traceId)
                   .run(() -> {
                       processRequest();
                   });
    }
    
    private void processRequest() {
        log("Starting request processing");
        authenticateUser();
        fetchData();
        log("Request processing complete");
    }
    
    private void authenticateUser() {
        log("Authenticating user");
        // Authentication logic
    }
    
    private void fetchData() {
        log("Fetching data from database");
        // Database operations
    }
    
    private void log(String message) {
        String requestId = REQUEST_ID.get();
        String userId = USER_ID.get();
        String traceId = TRACE_ID.get();
        System.out.printf("[%s][%s][%s] %s%n", traceId, requestId, userId, message);
    }
}

// Usage
WebRequestHandler handler = new WebRequestHandler();
handler.handleRequest("REQ-001", "user123", "TRACE-XYZ");

6. Structured Concurrency (5th Preview) JEP 505

• Structured Concurrency treats concurrent tasks as a single unit of work.
• Simplifies error handling and cancellation in multi-threaded code.
• Works seamlessly with virtual threads.

Traditional Concurrent Code

public UserData fetchUserData(String userId) throws Exception {
    ExecutorService executor = Executors.newCachedThreadPool();
    
    try {
        Future<Profile> profileFuture = executor.submit(() -> fetchProfile(userId));
        Future<Orders> ordersFuture = executor.submit(() -> fetchOrders(userId));
        Future<Preferences> prefsFuture = executor.submit(() -> fetchPreferences(userId));
        
        Profile profile = profileFuture.get();
        Orders orders = ordersFuture.get();
        Preferences prefs = prefsFuture.get();
        
        return new UserData(profile, orders, prefs);
    } finally {
        executor.shutdown();
    }
}

With Structured Concurrency (Java 25)

public UserData fetchUserData(String userId) throws Exception {
    try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
        // Fork all tasks
        Supplier<Profile> profile = scope.fork(() -> fetchProfile(userId));
        Supplier<Orders> orders = scope.fork(() -> fetchOrders(userId));
        Supplier<Preferences> prefs = scope.fork(() -> fetchPreferences(userId));
        
        // Wait for all to complete
        scope.join().throwIfFailed();
        
        // All tasks succeeded - collect results
        return new UserData(profile.get(), orders.get(), prefs.get());
    }  // Automatic cleanup
}

ShutdownOnSuccess Pattern

public class MultiServerQuery {
    public String queryFastestServer(List<String> serverUrls) throws Exception {
        try (var scope = new StructuredTaskScope.ShutdownOnSuccess<String>()) {
            // Query all servers in parallel
            for (String url : serverUrls) {
                scope.fork(() -> queryServer(url));
            }
            
            // Wait for first success, cancel others
            scope.join();
            
            return scope.result();
        }
    }
    
    private String queryServer(String url) {
        System.out.println("Querying: " + url);
        // Simulate API call
        return "Response from " + url;
    }
}

7. Generational Shenandoah GC JEP 521

• Generational Shenandoah is a low-pause garbage collector optimized for large heaps.
• Separates young and old generations for better performance.
• Excellent for latency-sensitive applications.

Enabling Generational Shenandoah

# Run Java with Generational Shenandoah GC
java -XX:+UseShenandoahGC -XX:ShenandoahGCMode=generational MyApp

Benefits Over Non-Generational GC

public class HighThroughputApp {
    public static void main(String[] args) {
        // Benefits of Generational Shenandoah:
        // 1. Lower pause times (typically < 10ms)
        // 2. Better throughput for apps with many short-lived objects
        // 3. More predictable performance
        
        // This app creates many temporary objects
        for (int i = 0; i < 1_000_000; i++) {
            String temp = "Processing item " + i;
            processBatch(generateData(1000));
        }
    }
    
    static List<String> generateData(int size) {
        List<String> data = new ArrayList<>();
        for (int i = 0; i < size; i++) {
            data.add("Item " + i);  // Short-lived objects
        }
        return data;
    }
    
    static void processBatch(List<String> batch) {
        // Process data
    }
}

GC Tuning Options

# Basic configuration
java -XX:+UseShenandoahGC \
     -XX:ShenandoahGCMode=generational \
     -Xms4g -Xmx4g \
     MyApp

# With additional tuning
java -XX:+UseShenandoahGC \
     -XX:ShenandoahGCMode=generational \
     -XX:+AlwaysPreTouch \
     -XX:+UseNUMA \
     -Xlog:gc*:file=gc.log \
     MyApp

8. Compact Object Headers JEP 519

• Compact Object Headers reduce object header size from 96-128 bits to 64 bits.
• Reduces memory footprint and improves cache locality.
• Particularly beneficial for applications with many small objects.

Impact on Memory Usage

public class MemoryComparison {
    // Each object typically has a 12-16 byte header
    static class SmallObject {
        int value;  // 4 bytes
        // Before: ~12-16 byte header + 4 bytes data = 16-20 bytes per object
        // After:  ~8 byte header + 4 bytes data = 12 bytes per object
    }
    
    public static void main(String[] args) {
        // Creating millions of small objects
        List<SmallObject> objects = new ArrayList<>();
        
        for (int i = 0; i < 10_000_000; i++) {
            objects.add(new SmallObject());
        }
        
        // With compact headers:
        // Saves ~4-8 bytes per object = 40-80 MB saved for 10M objects
        System.out.println("Objects created: " + objects.size());
    }
}

Real-World Benefit: Collections

public class LargeDataset {
    record Person(String name, int age) {}
    
    public static void main(String[] args) {
        // Applications with large collections benefit the most
        List<Person> people = new ArrayList<>();
        
        for (int i = 0; i < 5_000_000; i++) {
            people.add(new Person("Person" + i, 25 + (i % 50)));
        }
        
        // With compact headers:
        // - Reduced memory usage
        // - Better CPU cache utilization
        // - Improved performance for iteration and access
        
        long count = people.stream()
                          .filter(p -> p.age() > 40)
                          .count();
        
        System.out.println("People over 40: " + count);
    }
}

9. Key Derivation Function API JEP 510

• Key Derivation Function (KDF) API provides standard KDF operations in Java.
• Includes PBKDF2, HKDF, and other algorithms.
• Improves security for password hashing and key generation.

Password Hashing with PBKDF2

import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.PBEKeySpec;
import java.security.SecureRandom;
import java.security.spec.KeySpec;
import java.util.Base64;

public class PasswordHasher {
    private static final int ITERATIONS = 65536;
    private static final int KEY_LENGTH = 256;
    
    public static String hashPassword(String password, byte[] salt) throws Exception {
        KeySpec spec = new PBEKeySpec(
            password.toCharArray(),
            salt,
            ITERATIONS,
            KEY_LENGTH
        );
        
        SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256");
        byte[] hash = factory.generateSecret(spec).getEncoded();
        
        return Base64.getEncoder().encodeToString(hash);
    }
    
    public static byte[] generateSalt() {
        SecureRandom random = new SecureRandom();
        byte[] salt = new byte[16];
        random.nextBytes(salt);
        return salt;
    }
    
    public static void main(String[] args) throws Exception {
        String password = "MySecurePassword123!";
        byte[] salt = generateSalt();
        
        String hashedPassword = hashPassword(password, salt);
        
        System.out.println("Salt: " + Base64.getEncoder().encodeToString(salt));
        System.out.println("Hashed Password: " + hashedPassword);
    }
}

HKDF for Key Derivation

import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;

public class KeyDerivation {
    public static SecretKey deriveKey(byte[] inputKey, byte[] salt, byte[] info, int length) 
            throws NoSuchAlgorithmException, InvalidKeyException {
        // HKDF-based key derivation
        // Extract phase
        SecretKey prk = extract(inputKey, salt);
        
        // Expand phase
        return expand(prk, info, length);
    }
    
    private static SecretKey extract(byte[] inputKey, byte[] salt) {
        // HKDF-Extract implementation
        // Returns pseudo-random key
        return new SecretKeySpec(inputKey, "HmacSHA256");
    }
    
    private static SecretKey expand(SecretKey prk, byte[] info, int length) {
        // HKDF-Expand implementation
        // Expands PRK to desired length
        return prk;
    }
}

10. Vector API (10th Incubator) JEP 508

• Vector API enables SIMD (Single Instruction, Multiple Data) operations.
• Dramatically improves performance for numerical computations.
• Excellent for AI, machine learning, and data processing workloads.

Scalar vs Vector Operations

import jdk.incubator.vector.*;

public class VectorExample {
    static final VectorSpecies<Float> SPECIES = FloatVector.SPECIES_PREFERRED;
    
    // Traditional scalar approach
    public static void scalarMultiply(float[] a, float[] b, float[] result) {
        for (int i = 0; i < a.length; i++) {
            result[i] = a[i] * b[i];
        }
    }
    
    // Vector API approach - MUCH FASTER
    public static void vectorMultiply(float[] a, float[] b, float[] result) {
        int i = 0;
        int upperBound = SPECIES.loopBound(a.length);
        
        // Process vectors
        for (; i < upperBound; i += SPECIES.length()) {
            var va = FloatVector.fromArray(SPECIES, a, i);
            var vb = FloatVector.fromArray(SPECIES, b, i);
            var vc = va.mul(vb);
            vc.intoArray(result, i);
        }
        
        // Process remaining elements
        for (; i < a.length; i++) {
            result[i] = a[i] * b[i];
        }
    }
}

Matrix Multiplication

public class MatrixOperations {
    static final VectorSpecies<Double> SPECIES = DoubleVector.SPECIES_PREFERRED;
    
    public static double[] matrixVectorMultiply(double[][] matrix, double[] vector) {
        int rows = matrix.length;
        int cols = matrix[0].length;
        double[] result = new double[rows];
        
        for (int i = 0; i < rows; i++) {
            double sum = 0.0;
            int j = 0;
            int upperBound = SPECIES.loopBound(cols);
            
            // Vector processing
            var vsum = DoubleVector.zero(SPECIES);
            for (; j < upperBound; j += SPECIES.length()) {
                var vrow = DoubleVector.fromArray(SPECIES, matrix[i], j);
                var vvec = DoubleVector.fromArray(SPECIES, vector, j);
                vsum = vrow.mul(vvec).add(vsum);
            }
            sum = vsum.reduceLanes(VectorOperators.ADD);
            
            // Process remaining elements
            for (; j < cols; j++) {
                sum += matrix[i][j] * vector[j];
            }
            
            result[i] = sum;
        }
        
        return result;
    }
}

Performance Comparison

public class VectorPerformanceBenchmark {
    public static void main(String[] args) {
        int size = 10_000_000;
        float[] a = new float[size];
        float[] b = new float[size];
        float[] result = new float[size];
        
        // Initialize arrays
        for (int i = 0; i < size; i++) {
            a[i] = i * 1.5f;
            b[i] = i * 2.5f;
        }
        
        // Scalar approach
        long start = System.nanoTime();
        VectorExample.scalarMultiply(a, b, result);
        long scalarTime = System.nanoTime() - start;
        
        // Vector approach
        start = System.nanoTime();
        VectorExample.vectorMultiply(a, b, result);
        long vectorTime = System.nanoTime() - start;
        
        System.out.printf("Scalar time: %.2f ms%n", scalarTime / 1_000_000.0);
        System.out.printf("Vector time: %.2f ms%n", vectorTime / 1_000_000.0);
        System.out.printf("Speedup: %.2fx%n", (double) scalarTime / vectorTime);
        // Typical speedup: 2-8x depending on CPU architecture
    }
}

11. JFR Enhancements

Java 25 includes several Java Flight Recorder (JFR) improvements for better observability.

JFR CPU-Time Profiling JEP 509

• More accurate CPU time measurement
• Better profiling for multithreaded applications
• Reduced overhead during profiling

public class ProfilingExample {
    public static void main(String[] args) {
        // Enable JFR programmatically
        // Run with: java -XX:StartFlightRecording=filename=recording.jfr
        
        // CPU-intensive work
        for (int i = 0; i < 1_000_000; i++) {
            heavyComputation(i);
        }
    }
    
    static double heavyComputation(int input) {
        double result = 0;
        for (int i = 0; i < 1000; i++) {
            result += Math.sqrt(input + i) * Math.log(input + i + 1);
        }
        return result;
    }
}

JFR Method Timing & Tracing JEP 520

# Enable method timing for specific packages
java -XX:StartFlightRecording=filename=trace.jfr \
     -XX:FlightRecorderOptions=stackdepth=256 \
     -XX:+FlightRecorder \
     MyApplication

# Analyze with jfr tool
jfr print --events jdk.ExecutionSample trace.jfr

12. Stable Values (Preview) JEP 502

• Stable Values are immutable values treated as constants by the JVM.
• Enables aggressive optimizations while maintaining flexibility.
• Better than final fields for lazy initialization patterns.

Traditional Final Fields

public class Configuration {
    // Must be initialized in constructor
    private final String apiKey;
    private final int maxConnections;
    
    public Configuration() {
        this.apiKey = loadApiKey();  // Computed during construction
        this.maxConnections = 100;
    }
    
    private String loadApiKey() {
        // Complex initialization
        return System.getenv("API_KEY");
    }
}

With Stable Values (Java 25 Preview)

import jdk.internal.vm.annotation.Stable;

public class Configuration {
    // Can be initialized after construction
    @Stable private String apiKey;
    @Stable private int maxConnections;
    
    public void initialize() {
        // Lazy initialization
        if (this.apiKey == null) {
            this.apiKey = loadApiKey();
            this.maxConnections = 100;
        }
    }
    
    private String loadApiKey() {
        return System.getenv("API_KEY");
    }
}

13. Key Takeaways for Interview Preparation

Most Important Features to Master

1. Primitive Types in Patterns ⭐⭐⭐

   • Direct pattern matching with primitives
   • Cleaner switch expressions
   • Reduces boilerplate code

2. Flexible Constructor Bodies ⭐⭐⭐

   • Pre-super validation
   • More natural constructor flow
   • Better error handling

3. Generational Shenandoah GC ⭐⭐

   • Low-latency garbage collection
   • Better for large heaps
   • Predictable performance

4. Scoped Values ⭐⭐

   • Thread-safe context sharing
   • Better than ThreadLocal
   • Perfect for virtual threads

5. Vector API ⭐

   • SIMD operations in Java
   • Massive performance gains
   • Important for AI/ML workloads

Interview Discussion Points

• LTS Release: Java 25 continues the LTS cadence with enterprise-ready features
• Performance: Compact headers and Vector API bring significant speed improvements
• Developer Experience: Simpler syntax with flexible constructors and instance main
• Observability: Enhanced JFR capabilities for better production monitoring
• Security: Standardized KDF API for modern cryptography

Common Interview Questions

1. "What's new in Java 25?"

   • Lead with Primitive Types in Patterns and Flexible Constructors
   • Mention Generational Shenandoah GC
   • Discuss Scoped Values becoming final
   • Emphasize it's an LTS release

2. "How do Primitive Patterns improve code?"

   • Eliminates boxing/unboxing
   • Cleaner switch expressions
   • More type-safe
   • Better performance

3. "What are Scoped Values and why use them?"

   • Immutable thread-safe context
   • Automatic cleanup
   • Better than ThreadLocal for virtual threads
   • No memory leaks

4. "Explain Flexible Constructor Bodies"

   • Validation before super()
   • More natural constructor flow
   • Reduces boilerplate
   • Better encapsulation

5. "When would you use Vector API?"

   • Numerical computations
   • AI/ML workloads
   • Image/audio processing
   • Any SIMD-friendly operations

Migration from Java 21 to Java 25

Key Changes:

• Primitive patterns in switch (preview)
• Flexible constructor bodies
• Scoped Values now final
• Generational Shenandoah GC available
• Compact object headers reduce memory

Benefits:

• Cleaner, more expressive code
• Better performance (GC, memory, compute)
• Enhanced security (KDF API)
• Improved observability (JFR enhancements)
• LTS support until 2033+

Code Comparison: Java 21 vs Java 25

// JAVA 21 Style
public void processValue(Object obj) {
    if (obj instanceof Integer boxed) {
        int i = boxed;  // Unboxing needed
        System.out.println("Value: " + i);
    }
}

public class User {
    private final String name;
    
    public User(String name) {
        super();
        if (name == null) {
            throw new IllegalArgumentException();
        }
        this.name = name;
    }
}

// JAVA 25 Style - much cleaner!
public void processValue(Object obj) {
    if (obj instanceof int i) {  // Direct primitive pattern
        System.out.println("Value: " + i);
    }
}

public class User {
    private final String name;
    
    public User(String name) {
        if (name == null) {  // Validation before super()
            throw new IllegalArgumentException();
        }
        super();
        this.name = name;
    }
}

Summary

Java 25 is a major LTS release that brings together modern language features and performance improvements:

✅ Primitive Types in Patterns - Cleaner pattern matching
✅ Flexible Constructor Bodies - Natural validation flow
✅ Scoped Values - Thread-safe context (final)
✅ Generational Shenandoah - Low-latency GC
✅ Compact Object Headers - Reduced memory footprint
✅ Vector API - SIMD performance gains
✅ Enhanced JFR - Better observability
✅ KDF API - Modern cryptography support
✅ LTS Support - Production-ready until 2033+

Perfect for interviews because:

• Latest LTS release with modern features
• Combines language improvements and performance gains
• Shows Java's evolution toward simplicity
• Demonstrates commitment to performance and security
• Important for production applications

Resources:

• Oracle Java 25 Announcement
• OpenJDK Java 25 Documentation
• Java 25 Features Blog