abstract class Vehicle {
  // abstract method: no body, subclasses must fill it in
  public abstract void start();

  // regular method shared by all vehicles
  public void fuelUp() {
    System.out.println("Filling the tank");
  }
}

class Car extends Vehicle {
  @Override
  public void start() {
    System.out.println("Turn the key, engine runs");
  }
}

public class Main {
  public static void main(String[] args) {
    // Vehicle v = new Vehicle(); // error: cannot instantiate
    Vehicle v = new Car();
    v.start();   // Turn the key, engine runs
    v.fuelUp();  // Filling the tank
  }
}