الأصناف المختومة وأنماط السجلات

public sealed interface Shape permits Circle, Square, Triangle {}

public final class Circle implements Shape {
    public double radius;
    public Circle(double radius) { this.radius = radius; }
}

public final class Square implements Shape {
    public double side;
    public Square(double side) { this.side = side; }
}

public final class Triangle implements Shape {
    public double base, height;
    public Triangle(double base, double height) {
        this.base = base;
        this.height = height;
    }
}

public sealed interface Shape permits Circle, Square, Triangle {}

public non-sealed class Circle implements Shape {
    // أي صنف آخر يمكنه أن يرث Circle الآن
}

static double area(Shape shape) {
    return switch (shape) {
        case Circle c   -> Math.PI * c.radius * c.radius;
        case Square s   -> s.side * s.side;
        case Triangle t -> 0.5 * t.base * t.height;
        // لا حاجة لـ default — المترجم يتأكد أن كل الحالات مغطاة
    };
}

public sealed interface Result<T> permits Success, Failure {}
public record Success<T>(T value) implements Result<T> {}
public record Failure<T>(String error) implements Result<T> {}

public record Point(int x, int y) {}

// الطريقة التقليدية:
if (obj instanceof Point p) {
    int x = p.x();
    int y = p.y();
}

// منذ Java 21 — تفكيك مباشر:
if (obj instanceof Point(int x, int y)) {
    System.out.println(x + y);
}

static String describe(Object obj) {
    return switch (obj) {
        case Point(int x, int y) when x == y -> "على القطر: (" + x + ", " + y + ")";
        case Point(int x, int y)             -> "نقطة: (" + x + ", " + y + ")";
        default                              -> "غير معروف";
    };
}

public record Point(int x, int y) {}
public record Line(Point start, Point end) {}

static void printLine(Object obj) {
    if (obj instanceof Line(Point(int x1, int y1), Point(int x2, int y2))) {
        System.out.println("من (" + x1 + "," + y1 + ") إلى (" + x2 + "," + y2 + ")");
    }
}