Access modifier on abstract classes

Question

If I have an abstract class like

public abstract class Player
{
    //fields
    private Sport _sport;

    //properties
    protected Sport Sport
    {
        get { return _sport; }
        set { _sport = value; }
    }      
}

Is this protected access modifier redundant since abstract cannot be instantiated?

Answer 1

Is this protected access modifier redudant since abstract cannot be instantiated?

No, absolutely not. Consider:

Player player = new FootballPlayer();
Sport sport = player.Sport;

That would be valid if Sport were declared as a public property rather than protected. Of course, that may actually be what you want, but currently only code in derived classes (and within Player itself) can access the Sport property.

Note that your entire property would be simpler as an equivalent automatically implemented property though:

protected Sport Sport { get; set; }

Or to allow public getting but protected setting:

public Sport Sport { get; protected set; }

Answer 2

No, protected in abstract class is not redundant because it makes the derived-implementing classes to "have"-derive:

protected Sport Sport

Instead of:

public Sport Sport

And if you used private or removed the modifier completely, then sport would be visible only for the abstract class itself.

For example:

public abstract class Player
{
    // Changed to auto property to save some key strokes...
    protected Sport Sport { get; set;}
}

public RealPlayer : Player
{
    public void Foo(Sport sport)
    {
        this.Sport = sport; // Valid
    }
}

In some other class...

var realPlayer = new RealPlayer();
realPlayer.Sport // Compilation error.