Require override of specific methods of a non-abstract class

Question

Is it possible to have a class defined like

public class MyClass
{
    public void methodA(){} // Inherit
    public void methodB(){} // Inherit
    public void methodC(){} // Require override
}

and then have all classes which extend from MyClass to be required to override methodC() but just simply inherit methodA() and methodB()?

If it is possible, how does one do it? If it's not possible, can you propose an alternative solution to achieve a similar result?

EDIT:

I need a non-abstract class because I want to be able to instantiate this class too.

Solution 1

You cannot require an override of a non-abstract method.

Maybe you can do something similar to the template method pattern:

 public final void methodC() { methodC1(); someMoreLogic(); methodC2();}

 protected abstract void methodC1();

 protected abstract void methodC2();

Here methodC encapsulates a fixed algorithm that calls into pieces that have to be supplied by the subclasses.

Solution 2

You would have to make your base class abstract.

public abstract class MyClass
{
    public void methodA(){} // Inherit
    public void methodB(){} // Inherit
    public abstract void methodC(); // Require override
}

Solution 3

I don't think you do exactly what you want. Alternatively, create MyBaseClass as an abstract class with methodC() abstract implementations for methodA() and methodB(). Derive MyClass from it, adding an implementation for methodC(). Any classes that you do not want to have inherit that implementation should directly subclass MyBaseClass rather than MyClass.

Solution 4

If you want a method to be just inherited use final keyword. To force overriding make it abstract. However, only non-abstract child classes will have to override it.

Solution 5

AFAIK there is no way to force override a method in Java with out abstract.

You can achive with abstract class by making the method as abstract method.

View more solutions

Comments

[brain56]

It is specified in the question that the class must be non-abstract.

[EJK]

Yes, and in the question, you stated that "if it is not possible can you propose an alternative solution"?

[hansvb]

The question also does not give any background or motivation as to why it must be non-abstract.

[brain56]

OK, I see your point now. It's just that the answer wasn't provided clearly. I thought you were another one of those who don't read the question well. Sorry, I withdraw my downvote.

[msysmilu]

OP edit: I need a non-abstract class because I want to be able to instantiate this class too.

[Slobodan Pejic]

Java does not have a virtual keyword, and methods are virtual by default. The final keyword makes methods non-virtual.