Question

Possible Duplicate:
force base class to use its own method and not overrided method

Suppose I have these classes — sorry, it’s kind of hard to think of a simple example here; I don’t want any why-would-you-want-to-do-that answers! –:

class Squarer
{
    public void setValue(int v)
    {
        mV = v;
    }
    public int getValue()
    {
        return mV;
    }
    private int mV;
    public void square()
    {
        setValue(getValue() * getValue());
    }
}

class OnlyOddInputsSquarer extends Squarer
{
    @Override
    public void setValue(int v)
    {
        if (v % 2 == 0)
        {
            print("Sorry, this class only lets you square odd numbers!")
            return;
        }
        super.setValue(v);
    }
}

// auto s = new OnlyOddInputsSquarer();
OnlyOddInputsSquarer s = new OnlyOddInputsSquarer();
s.setValue(3);
s.square();

This won’t work. When Squarer.square() calls setValue(), it will go to OnlyOddInputsSquarer.setValue() which will reject all its values (since all squares are even). Is there any way I can override setValue() so that all the functions in Squarer still use the method defined there?

PS: Sorry, Java doesn’t have an auto keyword you haven’t heard about! Wishful thinking on my part.

Edit: I can’t modify Squarer!

Answer 1

It seems to me that the class Squarer is not well designed. If you really need a dirty trick to make this work, you could also override the method square():

class OnlyOddInputsSquarer extends Squarer
{
    @Override
    public void setValue(int v)
    {
        if (v % 2 == 0)
        {
            print("Sorry, this class only lets you square odd numbers!")
            return;
        }
        super.setValue(v);
    }
    @Override
    public void square()
    {
        super.setValue(getValue() * getValue());
    }
}

But… a square of a odd number is not even, so this should not really be a problem. I suppose this is just an example and your real problem is different.

Edit: OK, if this doesn’t work, there is even a dirtier method: in setValue check the stack and if it was called from square call super.setValue instead. I don’t recommend this, but If you really really need to get this done, check here to see how to do it.