What would be the right modifier?

Question

I have the following class with some methods and I would like to use this as a base class of another class.

public class BaseClass 
{
    public string DoWork(string str)
    {
        // some codes...
    }

    // other methods...
}

I don't want this class to be instantiated, but the derived class should still use the original implementation of the methods of its base class.

Is it possible? What should be my modifier?

@yonan2236 no. Abstract classes can contain concrete methods and properties. Otherwise they wouldn't really be that different from interfaces (apart from declaring non-public members) — Konrad Morawski, Sep 23 '13 at 10:45
@yonan2236 You can have implementation. It's the `interface` that don't have implementation. — John Woo, Sep 23 '13 at 10:46
Is this also true for Java? Does abstract in C# works the same in Java? — yonan2236, Sep 23 '13 at 10:48

John Woo · Accepted Answer · 2013-09-23T10:50:05.273

6

Since you don't want this class to be instantiated, make it an abstract class. You can still have implementation on the class.

abstract

snippet,

public abstract class BaseClass 
{
    public virtual string DoWork(string str)
    {
        // can have implementation here
        // and classes that inherits can overide this method because of virtual.
    }

    // other methods...
}

edited Sep 23 '13 at 10:50

answered Sep 23 '13 at 10:44

John Woo

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why is the method virtual? – yonan2236 Sep 23 '13 at 10:48
@yonan2236 so the method can be overridden. – John Woo Sep 23 '13 at 10:49
oh, so it means the derived class can have its own implementation of `DoWork` method? right? – yonan2236 Sep 23 '13 at 10:50
@yonan2236 exactly `:)` – John Woo Sep 23 '13 at 10:50
nice! this is what I'm trying to achive. Many thanks @491243! – yonan2236 Sep 23 '13 at 10:51
where you from Philippines? – yonan2236 Sep 23 '13 at 10:52
you can have the default implementation if you don't override this method. yep from dumaguete city `:)` – John Woo Sep 23 '13 at 10:53
I have friends in the Philippines : ) – yonan2236 Sep 23 '13 at 10:54
@Mr.Smith it's not override, but [shadowing](http://stackoverflow.com/questions/392721/difference-between-shadowing-and-overriding-in-c) and it needs to have `new` keyword. – John Woo Sep 23 '13 at 11:01

score 6 · Answer 2 · answered Sep 23 '13 at 10:44

6

Make BaseClass abstract:

public abstract class BaseClass 
{
    // Only available to BaseClass
    private string _myString;

    public string DoWork(string str)
    {
        // Available to everyone
        return _myString;
    }

    protected void DoWorkInternal() {
        // Only available to classes who inherit base class
    }
}

This way, you can define your own code within BaseClass - but it cannot be initialized directly, it must be inherited from.

answered Sep 23 '13 at 10:44

CodingIntrigue

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@Mr.Smith I'm not sure. OP says "but the derived class should still use the original implementation of the methods of its base class". I think he does not want `virtual`. – Paolo Falabella Sep 23 '13 at 10:51

What would be the right modifier?

2 Answers2