继承一个重载方法

Question

I'm fairly new to C# and OOP, and I have a question in regards to inheritance.

Say I have:

public abstract class Command
{
    protected Command()
    {
    }

    public abstract string Execute();

    public abstract string Execute(object o);
}

public class CommandA : Command
{
    public override string Execute()
    {
    }
}

public class CommandB : Command
{
    public override string Execute(object o)
    {
    }
}

There are obvious errors due to CommandA not implementing Execute(object o) and CommandB not implementing Execute() .

My question, then, is whether there is code I need to implement to avoid these errors? Are empty methods allowed?

Answer 1

You're abusing the use of abstract if you're expecting sub-classes to not actually implement some of the methods. abstract is used to enforce that the base class must implement the functionality. What should happen if someone called new CommandB().Execute() ?

In some cases, a design may be incorrect and you end up in the situation you're in. In these cases, its somewhat common (though in my opinion a code smell), to do the following:

public class CommandA : Command
{
    public override string Execute()
    {
    }

    public override string Execute(object o)
    {
        throw new NotImplementedException();
    }
}

A somewhat cleaner approach:

public abstract class Command
{
    protected Command()
    {
    }

    public abstract string Execute(object o = null);
}

Though you're still going to have to deal with the fact that someone may pass an object to CommandA .

If the commands have such different behaviour, it's likely they shouldn't both be subclassing the same abstract class.