Can we declare a variable as Abstract ?

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Can we declare a variable as Abstract ?
If Yes then What is the use of defining a variable as abstract in a Abstract Class..?

Posted 10-Sep-14 20:16pm

Sooraj_Singh

Updated 10-Sep-14 21:40pm

Richard MacCutchan

v2

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3 solutions

Solution 2

No you cannot.
When you declare a variable you declare an instance of the class/struct you specified.
Abstract classes cannot be directly instantiated.

And what would be the purpose of an abstract variable?

http://en.wikipedia.org/wiki/Abstract_type[^]

Posted 10-Sep-14 20:29pm

George Jonsson

Updated 10-Sep-14 20:31pm

v2

Solution 3

Yes, you can, although you actually define abstract PROPERTIES, not VARIABLES. I don't think declaring variables is even possible...but I admit I am NOT sure about this.

Use: forcing the inheritor of the class to implement that particular functionality.

Say you have an invoice class, order class and return class,all of them dealing with your goods (selling, receiving from your supplier and returns from buyers). And they all have some common things to do, they have headers with two people / firm details (sender, receiver), item list, total price etc...

What you want to force everyone is to have totalAmount and totalTax fields...you would declare them Abstract and anyone inheriting from your abstract class would have to implement it (even if it returned always the same (say tax = 0) for that particular implementation.

Posted 10-Sep-14 20:33pm

Sinisa Hajnal

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OriginalGriff · Accepted Answer · 2014-09-10T20:27:00

No.
You can only declare classes as abstract, and variables as references to classes (or as value types).
You can declare a variable as a reference to an abstract class, that's fine:

C#

public abstract class MyBase { ... }
public class MyDerived : MyBase { ... }
private void MyMethod()
   {
   MyBase base = new MyDerived();
   }

And base can hold a reference to any class derived from MyBase.

Similarly, within the abstract base class, you can't declare an abstract field:

C#

public abstract string myString;

Because the derived class would have to match the signature exactly - so where is the point? The field may as well be defined in the base class.
You can however declare abstract properties:

C#

public abstract class MyBase
    {
    public abstract string MyString { get; protected set; }
    }

And then the derived classes must provide the implementation.