How can you explain the difference between an interface and an abstract class to a non-programmer? [duplicate]

Answer 1

(In some languages, abstract class is used the same way as an interface, so it may be confusing)

A handful of classes that all have a certain common interface is like a handful of words that can fill in the the blank in a sentence. Example:

• ____ has wings
• Chicken has wings
• Airbus A320 has wings

However, the classes themselves, while they can all fit the blank in the sentence, do not have any relatioship in between. Chicken is a fowl while Airbus A320 is an aircraft. The only commonality is that they both have something that we call "wings". (You can also say that the true meanings of the "wings" are different in the two situations.)

class IHasWings : public IUnknown
{
public:
    // IUnknown methods: (Inherited)
    // IHasWings methods:
    virtual HRESULT GetWingSpan([out] double* pdblWingSpan) = 0;
    virtual HRESULT IsWingMovable([out] BOOL* pIsMovable) = 0;
    virtual HRESULT IsWingDetachable([out] BOOL* pIsDetachable) = 0;
};

class Chicken : public ... ..., public IHasWings
{
};

class AirbusA320 : public ... ..., public IHasWings
{
};