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  1. #1
    Kreuz14 is offline Member
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    Jan 2008
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    Default Inheritance, methods, and toString...

    Java Code:
        Vehicle [ ] acme = new Vehicle [5];
        acme[0] = new LightTruck(111, "Elmer Fudd", "GM", 500);
        acme[1] = new Car(222, "Wile E Coyote", "Ferrari", 2, 10);
        acme[2] = new Passenger(333, "Foghorn Leghorn", "Toyota", 5);    
        acme[3] = new Commercial(444, "Daffy Duck", "Mack", 42000);
        acme[4] = new Vehicle(555, "The Roadrunner", "Honda");
        for(int i = 0; i < acme.length; i++)
          System.out.println(acme[i].toString() + "\n");
        acme[0].changeCapacity(250); //ERRORS HERE
    In the above code, LightTruck/Car/Etc extends Vehicle.
    All the classes have their own toString method which print different things.
    LightTruck has a method called changeCapacity.

    The loop works and all the different toString methods return different values according to how its defined in the subclass (including private instance variables from the subclass).

    But why does changeCapacity not work and errors? The error log seems to suggest that it is because the compiler checks the Vehicle class for the changeCapacity method, but if thats true, then how come toString works? Wouldn't toString() simply return what is only in the Vehicle method?

  2. #2
    CaptainMorgan's Avatar
    CaptainMorgan is offline Moderator
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    Dec 2007
    NewEngland, US
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    The object located at acme[0] is a reference to a LightTruck object, but you are actually calling changeCapacity(int) on a Vehicle object. Where is changeCapacity(int) defined? If it's not in the Vehicle class, you may want to put it there and try again.

    To answer your question about toString(), think of it as a universally assigned method to all objects/classes. Every object gets a specific set of methods defined here. From that link, you can see that toString() is defined there. If you've defined toString() methods in your Vehicle subclasses, then you've essentially overridden definitions higher up the hierarchy.
    Last edited by CaptainMorgan; 04-01-2008 at 10:15 PM.
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