A sealed class, in C#, is a class that cannot be inherited by any class but 

can be instantiated. The design intent of a sealed class is to indicate that 

the class is specialized and there is no need to extend it to provide any 

additional functionality through inheritance to override its behavior.

​

Example: 

    namespace Account;

    sealed class BankAccount {...}

The sealed keyword is used to prevent unintended derivation from a class. 

A sealed class cannot be an abstract class. 

if (vehicle instanceof Car car) {

    return car.getNumberOfSeats();

} else if (vehicle instanceof Truck truck) {

    return truck.getLoadCapacity();

} else {

    throw new RuntimeException("Unknown instance of Vehicle");

}

public sealed interface Vehicle permits Car, Truck {

​

    String getRegistrationNumber();

​

}

​

public record Car(int numberOfSeats, String registrationNumber) implements Vehicle {

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    @Override

    public String getRegistrationNumber() {

        return registrationNumber;

    }

​

    public int getNumberOfSeats() {

        return numberOfSeats;

    }

​

}

​

public record Truck(int loadCapacity, String registrationNumber) implements Vehicle {

​

    @Override

    public String getRegistrationNumber() {

        return registrationNumber;

    }

​

    public int getLoadCapacity() {

        return loadCapacity;

    }

​

}