Java versions

public Sub(Certificate certificate) {
    var publicKey = certificate.getPublicKey();
    if (publicKey == null)
        throw new IllegalArgumentException("null certificate");
    final byte[] byteArray = switch (publicKey) {
        case RSAKey rsaKey -> ...
        case DSAPublicKey dsaKey -> ...
        ...
        default -> ...
    };
    super(byteArray);
}

void main() {
    System.out.println("Hello World!");
}

try (var _ = ScopedContext.acquire()) {    // Unnamed variable
    ... no use of acquired resource ...
} catch (Exception _) { ... }

...stream.collect(Collectors.toMap(
    String::toUpperCase,
    _ -> "NODATA"))    // Unnamed variable

// file MainApplication.java
public class MainApplication {
    public static void main(String[] args) {
        Person p = new Person("Billy", "Korando");
        System.out.println("Hello, " + p.toString() + "!");
    }
}

// file Person.java
record Person(String fName, String lName) {
    public String toString(){
        return fName + " " + lName;
    }
}

$ java MainApplication.java
Hello Billy Korando!

interface SequencedCollection<E> extends Collection<E> {
    // new method
    SequencedCollection<E> reversed();
    // methods promoted from Deque
    void addFirst(E);
    void addLast(E);
    E getFirst();
    E getLast();
    E removeFirst();
    E removeLast();
}

interface SequencedSet<E> extends Set<E>, SequencedCollection<E> {
    SequencedSet<E> reversed();    // covariant override
}

interface SequencedMap<K,V> extends Map<K,V> {
    // new methods
    SequencedMap<K,V> reversed();
    SequencedSet<K> sequencedKeySet();
    SequencedCollection<V> sequencedValues();
    SequencedSet<Entry<K,V>> sequencedEntrySet();
    V putFirst(K, V);
    V putLast(K, V);
    // methods promoted from NavigableMap
    Entry<K, V> firstEntry();
    Entry<K, V> lastEntry();
    Entry<K, V> pollFirstEntry();
    Entry<K, V> pollLastEntry();
}

static void printSum(Object obj) {
    if (obj instanceof Point(int x, int y)) {
        System.out.println(x+y);
    }
}

static void printColorOfUpperLeftPoint(Rectangle r) {
    if (r instanceof Rectangle(ColoredPoint(Point p, Color c),
                               ColoredPoint lr)) {
        System.out.println(c);
    }
}

static void printXCoordOfUpperLeftPointWithPatterns(Rectangle r) {
    if (r instanceof Rectangle(ColoredPoint(Point(var x, var y), var c),
                               var lr)) {
        System.out.println("Upper-left corner: " + x);
    }
}

try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
    IntStream.range(0, 10_000).forEach(i -> {
        executor.submit(() -> {
            Thread.sleep(Duration.ofSeconds(1));
            return i;
        });
    });
}  // executor.close() is called implicitly, and waits

/**
 * The following code shows how to use {@code Optional.isPresent}:
 * {@snippet :
 * if (v.isPresent()) {
 *     System.out.println("v: " + v.get());
 * }
 * }
 */

/**
 * The following code shows how to use {@code Optional.isPresent}:
 * {@snippet file="ShowOptional.java" region="example"}
 */

public class ShowOptional {
    void show(Optional<String> v) {
        // @start region="example"
        if (v.isPresent()) {
            System.out.println("v: " + v.get());
        }
        // @end
    }
}

sealed interface Celestial
    permits Planet, Star, Comet { ... }

final class Planet implements Celestial { ... }
final class Star   implements Celestial { ... }
final class Comet  implements Celestial { ... }

record Range(int lo, int hi) {
    // Compact canonical validating constructor
    Range {
        if (lo > hi)  // referring here to the implicit constructor .parameters
            throw new IllegalArgumentException(String.format("(%d,%d)", lo, hi));
    }
}

record Rational(int num, int denom) {
    // Compact canonical normalizing constructor.
    Rational {
        int gcd = gcd(num, denom);
        num /= gcd;
        denom /= gcd;
    }
}

if (obj instanceof String s) {
    // `String s` is visible here.
}
// `String s` is NOT visible here.

if (!(obj instanceof String s)) {
    // `String s` is NOT visible here.
} else {
    // `String s` is visible here.
}

jpackage --name myapp --input lib --main-jar main.jar --type pkg

final String html = """
                    {
                        "message": "Hello world"
                    }
                    """;

java -XX:+UnlockExperimentalVMOptions -XX:+UseZGC -jar app.jar

java -XX:+UseZGC -jar app.jar

java -XX:+UnlockExperimentalVMOptions -XX:+UseShenandoahGC -jar myapp.jar

java -XX:+UseShenandoahGC -jar myapp.jar

Exception in thread "main" java.lang.NullPointerException:
        Cannot assign field "i" because "a" is null
    at Prog.main(Prog.java:5)