Question

Is there any keyword or design pattern for doing this?

Please check the update

public abstract class Root
{
    public abstract void foo();
}

public abstract class SubClass extends Root
{
    public void foo()
    {
        // Do something
        //---------------- Update -------------------//
        // This method contains important code
        // that is needed when I'm using a instance
        // of SubClass and it is no instance of any
        // other class extending SubClass

    }
}

public class SubberClass extends SubClass
{
    // Here is it not necessary to override foo()
    // So is there a way to make this necessary? 
    // A way to obligate the developer make again the override 
}

Thanks

Answer 1

If you are doing this, then you are probably abusing inheritance; inheritance, contrary to popular myth, is not intended for making custom hooks/handlers, but rather to enable alternative implementations.

If you want your user to provide some sort of function/hook/callback, then you should define an interface that provides just those methods that you need your user to define. Then you should require the user to pass in an instance of that interface to your object’s constructor or passed into the function that needs it.

Aggregation, delegation, and composition are frequently better and safer design patterns than inheritance; forcing other users to inherit from your class, is incredibly risky, as it provides the user with many opportunities to violate the contract of your class or to invalidate the invariant of your base class.