Java 20 APIs & Features

import java.util.concurrent.StructuredTaskScope;
import jdk.incubator.concurrent.ScopedValue;

// Define scoped values
public class UserContext {
    public static final ScopedValue<String> USER_ID = ScopedValue.newInstance();
    public static final ScopedValue<String> REQUEST_ID = ScopedValue.newInstance();
}

// Use scoped values
public void handleRequest(String userId, String requestId) {
    // Bind values to the scope
    ScopedValue.where(UserContext.USER_ID, userId)
        .where(UserContext.REQUEST_ID, requestId)
        .run(() -> {
            processRequest();
        });
}

private void processRequest() {
    // Access scoped values anywhere in the call stack
    String userId = UserContext.USER_ID.get();
    String requestId = UserContext.REQUEST_ID.get();
    
    System.out.println("Processing request " + requestId + " for user " + userId);
    
    // Call other methods - they can access the same values
    authenticateUser();
    logAction();
}

private void authenticateUser() {
    String userId = UserContext.USER_ID.get();
    System.out.println("Authenticating user: " + userId);
}

private void logAction() {
    String userId = UserContext.USER_ID.get();
    String requestId = UserContext.REQUEST_ID.get();
    System.out.println("Logging action for user " + userId + " request " + requestId);
}

import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.time.Duration;

// Enhanced virtual thread creation
Thread.ofVirtual()
    .name("worker-", 0)
    .start(() -> {
        System.out.println("Virtual thread: " + Thread.currentThread());
    });

// Virtual thread executor with improved performance
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
    List<Future<String>> futures = new ArrayList<>();
    
    // Submit many tasks efficiently
    for (int i = 0; i < 10_000; i++) {
        final int taskId = i;
        Future<String> future = executor.submit(() -> {
            // Simulate I/O operation
            Thread.sleep(Duration.ofMillis(50));
            return "Task " + taskId + " completed";
        });
        futures.add(future);
    }
    
    // Collect results
    for (Future<String> future : futures) {
        System.out.println(future.get());
    }
}

// Virtual threads with structured concurrency
try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
    Future<String> user = scope.fork(() -> findUser("john"));
    Future<Integer> orderCount = scope.fork(() -> countOrders("john"));
    
    scope.join();
    scope.throwIfFailed();
    
    System.out.println("User: " + user.resultNow());
    System.out.println("Orders: " + orderCount.resultNow());
}

// Enhanced pattern matching in switch
public String processValue(Object value) {
    return switch (value) {
        case String s when s.length() > 10 -> "Long string: " + s;
        case String s -> "Short string: " + s;
        case Integer i when i > 0 -> "Positive integer: " + i;
        case Integer i when i < 0 -> "Negative integer: " + i;
        case Integer i -> "Zero";
        case List<?> list when list.isEmpty() -> "Empty list";
        case List<?> list -> "List with " + list.size() + " elements";
        case Map<?, ?> map when map.isEmpty() -> "Empty map";
        case Map<?, ?> map -> "Map with " + map.size() + " entries";
        case null -> "null value";
        default -> "Unknown type: " + value.getClass().getSimpleName();
    };
}

// Record patterns with enhanced matching
record Point(int x, int y) {}
record Circle(Point center, double radius) {}

public String describeShape(Object shape) {
    return switch (shape) {
        case Circle(Point center, double radius) when radius > 10 -> 
            "Large circle at (" + center.x() + "," + center.y() + ")";
        case Circle(Point center, double radius) -> 
            "Small circle at (" + center.x() + "," + center.y() + ")";
        case Point(int x, int y) when x == 0 && y == 0 -> "Origin point";
        case Point(int x, int y) -> "Point at (" + x + "," + y + ")";
        default -> "Unknown shape";
    };
}

import java.foreign.MemorySegment;
import java.foreign.MemorySession;
import java.foreign.Linker;
import java.foreign.SymbolLookup;

// Allocate native memory
try (MemorySession session = MemorySession.openConfined()) {
    MemorySegment segment = session.allocate(100);
    // Use the segment for native operations
}

// Call a native function (e.g., strlen from libc)
Linker linker = Linker.nativeLinker();
SymbolLookup libc = SymbolLookup.loaderLookup();
var strlen = linker.downcallHandle(
    libc.lookup("strlen").get(),
    FunctionDescriptor.of(ValueLayout.JAVA_LONG, ValueLayout.ADDRESS)
);
long len = (long) strlen.invoke(MemorySegment.ofArray("hello".getBytes()));

import jdk.incubator.vector.*;

// Vector operations for high-performance computing
public class VectorExample {
    static final VectorSpecies<Float> SPECIES = FloatVector.SPECIES_PREFERRED;
    
    public static void vectorAdd(float[] a, float[] b, float[] c) {
        int i = 0;
        int upperBound = SPECIES.loopBound(a.length);
        
        for (; i < upperBound; i += SPECIES.length()) {
            FloatVector va = FloatVector.fromArray(SPECIES, a, i);
            FloatVector vb = FloatVector.fromArray(SPECIES, b, i);
            FloatVector vc = va.add(vb);
            vc.intoArray(c, i);
        }
        
        // Handle remaining elements
        for (; i < a.length; i++) {
            c[i] = a[i] + b[i];
        }
    }
    
    public static float vectorSum(float[] array) {
        FloatVector sum = FloatVector.zero(SPECIES);
        int i = 0;
        int upperBound = SPECIES.loopBound(array.length);
        
        for (; i < upperBound; i += SPECIES.length()) {
            FloatVector va = FloatVector.fromArray(SPECIES, array, i);
            sum = sum.add(va);
        }
        
        float result = sum.reduceLanes(VectorOperators.ADD);
        
        // Handle remaining elements
        for (; i < array.length; i++) {
            result += array[i];
        }
        
        return result;
    }
}