进阶题——Vehicle
abstract class Vehicle {
    public abstract void run();
}
class Car extends Vehicle {
    @Override
    public void run() {
        System.out.println("汽车在公路上行驶");
    }
}
class Bike extends Vehicle {
    @Override
    public void run() {
        System.out.println("自行车在道路上骑行");
    }
}
class Truck extends Vehicle {
    @Override
    public void run() {
        System.out.println("卡车在高速公路上运输货物");
    }
}
public class VehicleDemo {
    public static void main(String[] args) {
        Vehicle[] vehicles = new Vehicle[3];
        vehicles[0] = new Car();
        vehicles[1] = new Bike();
        vehicles[2] = new Truck();
        for (Vehicle vehicle : vehicles) {
            vehicle.run();
        }
    }
}