A question about inheritance / polymorphism

[gabriels]

Hi, i tried the following code:

<pre>

public class Parent {

}

public class FirstChild extends Parent {

}

public class SecondChild extends Parent {

}

public class Other {

    public void doSomething(Parent obj) {
        // some code
    }

    public void doSomething(FirstChild obj) {
        // some code
    }

    public void soSomething(SecondChild obj) {
        // some code
    }

}

public class Another {

    public static void main(String args[]) {

        other = new Other();

        Parent first = new FirstChild();
        Parent second = new SeconChild();

        other.doSomething(first);
        other.doSomething(second);

    }

}

</pre>

In the last two lines doSomething(Parent) is called, but i want it to act like a virtual function, to activate the right overloaded function depending on the parameter run-time type. I know i can define doSomething() in Parent, FirstChild and SecondChild classes and it should work, but it's important that it will be in Other class. Is it possible?

[JosAH]

Hi, i tried the following code:

public class Another {

    public static void main(String args[]) {

        other = new Other();

        Parent first = new FirstChild();
        Parent second = new SeconChild();

        other.doSomething(first);
        other.doSomething(second);

    }

}

In the last two lines doSomething(Parent) is called, but i want it to act like a virtual function, to activate the right overloaded function depending on the parameter run-time type. I know i can define doSomething() in Parent, FirstChild and SecondChild classes and it should work, but it's important that it will be in Other class. Is it possible?

Overloading is a compiler issue; all that the compiler knows is that your variables first and second are Parent objects (it doesn't think much further) so it calls the method that takes a Parent parameter. Maybe the Visitor pattern (also called the Double Dispatch pattern) can be of help, i.e. your other class is the Visitor and calls a Parent object that calls the correct method in your Visitor again according to its real type.

kind regards,

Jos

[gabriels]

That solves my problem, thanks :-)