Liskov substitution Principle (LSP)

This rule of design pattern assure that if a class derived from base class then base class should be a proper substitute for derived class.

“The derived classes should be perfectly substitutable for their base classes”.

In the below example “Jeep” Class object is representing “Trucker” Object. AS per LSP principle it should be wrong.

/// <summary>

    /// Jeep Class

    /// </summary>

    public class Jeep

    {

        public virtual int Speed()

        {

            return 60;

        }

    }

    /// <summary>

    /// Truck Class inherit

    /// </summary>

    public class Trucker : Jeep

    {

        public override int Speed()

        {

            return 55;

        }

    }

 

 

Jeep jep = new Trucker();

            Console.WriteLine(jep.Speed().ToString()); 

Implementation of “Liskov substitution Principle”

                We must make sure that the new derived classes just extend without replacing the functionality of old classes. Otherwise the new classes can produce undesired effects when they are used in existing program modules.

/// <summary>

    /// Abstract  class for vechile

    /// </summary>

    public abstract class Vechile

    {

        public abstract int Speed();

    }

   

    /// <summary>

    /// Jeep Class

    /// </summary>

    public class Jeep : Vechile

    {

        public override int Speed()

        {

            return 60;

        }

    }

    /// <summary>

    /// Truck Class inherit

    /// </summary>

    public class Trucker : Jeep

    {

        public override int Speed()

        {

            return 55;

        }

    } 

I have implement new abstract class for Vehicle & it is derived for all classes. Ie “Jeep” derived from “Vehicle” and “trucker” derived from “Jeep”. But we can represent Both “Jeep” & “Trucker” object using “Vechile” object.

     Vechile vehicle = new Jeep();

            Console.WriteLine(vehicle.Speed().ToString());

            vehicle = new Trucker();

            Console.WriteLine(vehicle.Speed().ToString());