Classes (does this make sense?)

[Saaa]

My idea was to put everything all the fruits share in the same (abstract) 
super class.
I would also like the assert code to be in the super class as it is the same 
for all fruits.
Same for the color setter/getter.


> ///
>> Why is an interface better than a abstract class?
>> Where should I store the number (it should have been called color, my bad
>> )? Every fruit has the color variable.
>
> Interfaces may have these benefits:
> - it is possible for a class to implement more than one interface
> - implementation is completely seperate from the interface. This can lead 
> to
> more flexible code. Further, it means that the implementation is in one
> place, which is easier to maintain.
>
> When you make color a property, it's variable must be stored in the 
> classes
> that implement IFruit: Apple, Plum, etc, and would be a private field.
>
> Here is an example of how that could have some advantage:
>
> class Apple : IFruit
> {
>
>    int color()
>    {
>        return _color;
>    }
>
>    void rot()
>    {
>        _color = BROWN;
>    }
>
>
>    private int _color = GREEN; // GREEN is defined elsewhere
> }
>
> In this implementation, only inside the Apple class can the color be
> changed. This means that, when that code is correct color can be 
> guaranteed
> to always be in a valid state. Alternatively a setter can be implemented
> that checks for valid input:
>
> void color(int clr)
> {
>    if ( ! (clr == BROWN || clr == GREEN || clr == YELLOW) )
>        throw new Exception("invalid color for Apple");
>    _color = clr;
> }
>
> Yet another way to keep color always correct is to use an invariant:
>
> class Apple : IFruit
> {
>    invariant()
>    {
>        assert(clr == BROWN || clr == GREEN || clr == YELLOW,
>               "Apple's color is invalid");
>    }
> }
>
> When compiled with -unittest, the invariant is checked before and after
> every function in Apple is executed.