Do I really have a car in my garage? [duplicate]

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I’m a newbie to Java programming, trying to get the hang of OOP.

So I built this abstract class:

public abstract class Vehicle{....}

and 2 subclasses:

public class Car extends Vehicle{....}
public class Boat extends Vehicle{....}

Car and Boat also hold some unique fields and methods that aren’t common (don’t have the same name, so I can’t define an abstract method for them in Vehicle).

Now in mainClass I have setup my new Garage:

Vehicle[] myGarage= new Vehicle[10];
myGarage[0]=new Car(2,true);
myGarage[1]=new Boat(4,600);

I was very happy with polymorphism until I tried to access one of the fields that are unique to Car, such as:

boolean carIsAutomatic = myGarage[0].auto;

The compiler doesn’t accept that. I worked around this issue using casting:

boolean carIsAutomatic = ((Car)myGarage[0]).auto;

That works… but it doesn’t help with methods, just fields. Meaning I can’t do

(Car)myGarage[0].doSomeCarStuff();

So my question is – what do I really have in my garage? I’m trying to get the intuition as well as understand what’s going on “behind the scenes”.

for the sake of future readers, a short summary of the answers below:

  1. Yes, there’s a Car in myGarage[]
  2. Being a static typed language, the Java compiler will not lend access to methods/fields that are non-“Vehicle”, if accessing those through a data structure based on the Vehicle super class( such as Vehicle myGarage[])
  3. As for how to solve, there are 2 main approaches below:
    1. Use type casting, which will ease the compiler’s concerns and leave any errors in the design to run time
    2. The fact that I need casting says the design is flawed. If I need access to non-Vehicle capabilities then I shouldn’t be storing the Cars and Boats in a Vehicle based data structure. Either make all those capabilities belong to Vehicle, or use more specific (derived) type based structures
  4. In many cases, composition and/or interfaces would be a better alternative to inheritance. Probably the subject of my next question…
  5. Plus many other good insights down there, if one does have the time to browse through the answers.

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