Abstraction Vs. Interface Confusion

问题

Wait, before you start thinking, I would like to clear that I am NOT going to ask the routine differences between Interface and Abstract.

I had gone through the difference between Abstract and Interface in MSDN.

It is said :

By updating the base class, all inheriting classes are automatically updated with the change.
Interfaces, on the other hand, cannot be changed once created. If a new version of an interface is required, you must create a whole new interface.

See this : -

Can anyone prove this using following example: -

abstract class WashingMachine
{
   abstract public void Wash();
}


class Philips : WashingMachine
{
   public Philips() {  }

   override public void Wash(){//Wash code here....}
}

class Samsung : WashingMachine
{
   public Samsung() {  }

   override public void Wash(){//Wash code here....}
}

class Videocon : WashingMachine
{
   public Videocon() {  }

   override public void Wash(){//Wash code here....}
}

Now, If I added following new abstract method in WashingMachine : -

abstract public void Rinse(int loadSize);

How all inheriting classes (i.e. Philips/Samsung/Videocon) will automatically get updated with the change?

回答1:

They won't get updated - you still have to manually add an implementation of Rinse to each and every class that inherits from WashingMachine.

What I believe the MSDN says is that if you have a non-abstract method defined in an abstract class and you change that method, all classes that inherit from the abstract class will benefit from the change automatically.

回答2:

Your concrete derived types all need to provide an implementation of any inherited abstract member...thus your types will still need to provide a Rinse implementation when you modified the base.

http://msdn.microsoft.com/en-us/library/sf985hc5(v=vs.71).aspx

回答3:

This is a confusion programmers normally get when read difference between interface and abstract class. the line you refer is only true if the change in the abstract class is concrete. what i mean is you added a property or a method with implementation. Or if i am more specific, any change in base abstract class which does not make any concrete class abstract. Such change is possible in abstract classes and there is no way you can add such change in interface.

回答4:

How all inheriting classes (i.e. Philips/Samsung/Videocon) will automatically get updated with the change?

They will suddenly become non-compileable, isn't that an update?

But I'd like to point out that there's in fact no difference between abstract method in abstract class and method in interface. Main difference lies in the fact that abstract classes can have methods with implementation and interfaces can not.

In fact, I'd say that I don't like MSDN definition and find it confusing and somewhat misleading.

来源：https://stackoverflow.com/questions/11700446/abstraction-vs-interface-confusion

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