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Thread: Inheritance and Overriding help!

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    Default Inheritance and Overriding help!

    Hi,
    -->My problem is quite simple.
    -->I have a super class with a method public void add(int theValue)
    -->I have an interface with a method boolean add(int theValue)
    -->My subclass implements ISet which is my interface and extends my superclass
    -->I need to put in my subclass (SetInherit) a method public boolean add(int theValue) but apprently it is illegal to change the return type on and overridden method from the superclass.
    -->I need this boolean add(int theValue) method to check to see if the bag has the value, if it does I need it to return false and do nothing and if the value isn't in the bag I need it to send the value to the superclass and have it added to the bag.
    -->All I need is to know how to implement this method without changing the name. Thank you!


  2. #2
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    Default Re: Inheritance and Overriding help!

    Simple: copy-paste the method declaration, erase the abstract keyword (if any), remove the ending semi-colon, add curly braces, and implement the method.

    public Interface MyInterface
    {
        public void doIt();
    }
     
    public class Base implements MyInterface
    {
        // the overriden method doIt
        public void doIt()
        {
            // you're overriden implementation goes here
        }
    }

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    Default Re: Inheritance and Overriding help!

    Thanks but unfortunately that's not what I was looking for. It's along the lines but I already know how to do that. See I have the interface that has a boolean add(int theValue) but its "boolean". In the superclass the same method add is void not boolean. So here's my problem.
    public class BoundedBag
    {
        public void add(int theValue)
       {
            //stuff
       }
    }
     
    public interface Iset
    {
       boolean add(int theValue);
      //more methods
    }
     
    public class SetInherit extends BoundedBag implements Iset
    {
         //this is where I need to use public boolean add(int theValue)
        //unfortunately I tried to override using a different return type and it returned an illegal action.
    }
    Of course I left out the default constructors and such.
    Last edited by helloworld922; February 19th, 2011 at 09:56 AM.

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    Default Re: Inheritance and Overriding help!

    Ahh, I didn't see that. That's not allowed.

    Quote Originally Posted by Java Language Specification
    8.4.8.4 Inheriting Methods with Override-Equivalent Signatures
    It is possible for a class to inherit multiple methods with override-equivalent (§8.4.2) signatures.

    It is a compile time error if a class C inherits a concrete method whose signatures is a subsignature of another concrete method inherited by C.
    If you are able to modify either one of those classes, I would suggest you either slightly change the name of one, change the return type of one to match the other, or add a "dummy parameter" (this last one isn't really suggested). Otherwise, you cannot both implement that interface and extend the other class.

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    Default Re: Inheritance and Overriding help!

    You should consider throwing an exception instead of returning a boolean as a success indicator (e.g. DuplicateEntryException). It sounds like when the value is already in the bag, the method cannot complete (it fails). This is what exceptions are for, you really shouldn't be using boolean return values to indicate success or failure.

    This does mean that both the Iset method and the BoundedBag method should be declared to throw the exception.

    Incidentally, if the method has the same semantics in Iset and BoundedBag, why doesn't BoundedBag implement Iset?

    If the semantics are different for the two methods, you shouldn't try to make their signatures the same - it's asking for trouble. You should explicitly differentiate them by changing the name of one or both (let's face it, 'add(int)' is likely to cause clashes). Why not addItem(..) or even addBagItem(..), etc.
    Last edited by dlorde; February 24th, 2011 at 01:48 PM.

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