You defined that your garage will store vehicles, so you do not care what type of vehicles you have. The vehicles have common features like engine, wheel, behavior like moving.
The actual representation of these features might be different, but at abstract layer are the same.
You used abstract class which means that some attributes, behaviors are exactly the same by both vehicle. If you want to express that your vehicles have common abstract features then use interface like moving might mean different by car and boat. Both can get from point A to point B, but in a different way (on wheel or on water - so the implementation will be different)
So you have vehicles in the garage which behave the same way and you do not car about the specific features of them.
To answer the comment:
Interface means a contract which describes how to communicate with the outer world. In the contract you define that your vehicle can move, can be steered, but you do not describe how it will actually work, it is described in the implementation.By abstract class you might have functions where you share some implementation, but you also have function which you do not know how it will be implemented.
One example of using abstract class:
abstract class Vehicle {
protected abstract void identifyWhereIAm();
protected abstract void startEngine();
protected abstract void driveUntilIArriveHome();
protected abstract void stopEngine();
public void navigateToHome() {
identifyWhereIAm();
startEngine();
driveUntilIArriveHome();
stopEngine();
}
}
You will use the same steps by each vehicle, but the implementation of the steps will differ by vehicle type. Car might use GPS, boat might use sonar to identify where it is.
