C# abstract keyword

In this tutorial, we would learn about abstract keyword in c# programming language.

abstract: This modifier indicates that thing being modified has a missing or incomplete implementation.

This modifier in C# language applies to the following :

1. Class

2. Method

3. Properties

4. Indexers

5. Events

Abstract class

A class declared with abstract modifier is an abstract class.

• abstract classes are intended to be a base class of other classes - the developer can not create an Object of an abstract class.

• an abstract class can have both abstract methods ( methods with definition) and non-abstract methods (methods without definition).

• As an object can not be created for an abstract class, a derived class must be created for an abstract class.

    public abstract class Asset {
        public abstract decimal BuyPrice { get; }
        public abstract decimal SellPrice { get; }
        public abstract decimal CalculateProfit();
    }
    public class Stock : Asset {
        public override decimal BuyPrice => 100;
        public override decimal SellPrice => 150;
        public override decimal CalculateProfit() {
            return (SellPrice - BuyPrice);
        }
    }

• An abstract class must provide implementation for all interface members

• An abstract class that implements an interface might map the interface methods onto abstract methods.

    interface I {
        void M();
    }
    abstract class C : I {
        public abstract void M();
    }
  

Abstract methods / Properties

• abstract method declaration doesn't provide any implementation.

    public abstract class Asset {
            public abstract decimal CalculateProfit();
        }
  

• An abstract method is implicitly a virtual method - base class must provide its implementation.

• It is an error to use static or virtual modifiers in an abstract method declaration.

• Abstract method declarations are only permitted in abstract classes.

  

• Abstract properties behave like abstract methods, except for the differences in declaration and invocation syntax..

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