Call 'grand' parent function from child class in multi-level inheritance

Question

public class GrandParent
{
    public void walk()
    {
        ...
    }
}

public class Parent
{
    public void walk()
    {
        ...
    }
}

public class Child
{
    public void walk()
    {
        // Here in some cases I want to use walk method of GrandParent class
    }
}

Now in Child.walk(), I want to use GrandParent.walk() only in some cases. How can I do that? Since super.walk() will always use Parent.walk().

NOTE: (Please note that this is simplified example of a complex scenario)

NOTE2: Please only tell if there is a standard procedure of doing that. I have used a flag in parent class, which the child sets if it wants to use the method of GrandParent. But this sequence becomes very complex.

Can't you just cast the child instance to the grandparent type and call walk on that? — 0xCAFEBABE, Mar 11 '13 at 08:12
Just as a side note, you may be interested in knowing that you are breaking encapsulation by trying to access GrandParent functionality from Child. Merely a "good design" point, but I felt that it was relevant. For more, see http://stackoverflow.com/questions/586363/why-is-super-super-method-not-allowed-in-java — Rahul Banerjee, Mar 11 '13 at 08:13
@0xCAFEBABE The most specific implementation of the method is called. By casting the child to grandparent won't change the availability of the most specific implementation. — , Mar 11 '13 at 08:15
The terminology confuses me a bit, am used to hearing `walk` and `parent` used together when describing object trees, not class inheritance. — flup, Mar 11 '13 at 08:15
Seems like you have a design problem. You are not suppose to do that. It would be helpful to give us some background: Why you need to do this?? — codeMan, Mar 11 '13 at 08:17
@Real yep it is possible but that's not much different from creating a flag in parent classes. — , Mar 11 '13 at 08:57

score 8 · Answer 1 · answered Mar 11 '13 at 08:29

The problem here is in the decision to call the Parent function "walk". It should not have been called "walk" unless it is intended to be a complete functional replacement for the GrandParent walk().

If that decision cannot be changed, then the solution suggested in the existing answer from @zvzdhk is the best that can be done.

Ideally, the Parent walk() would be given a new name reflecting whatever is different about its function from the GrandParent walk(). Each of the functions could then be called from the Child class.

score 6 · Accepted Answer · edited May 23 '17 at 12:26

6

You could specify method for accessing parent's value like this:

public class GrandParent
{
    public void walk()
    {
        ...
    }
}

public class Parent
{
    public void walk()
    {
        ...
    }

    public void grandParentWalk()
    {
        super.walk();
    }
}

public class Child
{
    public void walk()
    {
        grandParentWalk();
    }
}

Call 'grand' parent function from child class in multi-level inheritance

2 Answers2

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