Strategy Pattern

Definition:

Identify the aspects of your application that vary and separate them from what stays the same

Sample Code: 

namespace StrategyPattern
{
    public abstract class Duck
    {
        protected FlyBehavior flyBehavior;
        protected QuackBehavior quackBehavior;

        public Duck() { }

        public abstract void display();

        public void swim()
        {
            Console.WriteLine("All ducks float");
        }
        
        public void performFly() 
        {
            flyBehavior.fly();
        }
        public void performQuack()
        {
            quackBehavior.quack();
        }
        public void setFlyBehavior(FlyBehavior behavior)
        {
            flyBehavior = behavior;
        }
        public void setQuackBehavior(QuackBehavior behavior)
        {
            quackBehavior = behavior;
        }
    }
    public interface FlyBehavior
    {
        void fly();
    }
    public interface QuackBehavior
    {
        void quack();
    }
    public class FlyWithWings : FlyBehavior
    {
        public void fly()
        {
            Console.WriteLine("Fly with wings");
        }
    }
    public class FlyNoWay : FlyBehavior
    {
        public void fly()
        {
            Console.WriteLine("Do nothing"); 
        }
    }
    public class Quack : QuackBehavior
    {
        public void quack()
        {
            Console.WriteLine("Duck is quacking");
        }
    }
    public class Squeak : QuackBehavior
    {
        public void quack()
        {
            Console.WriteLine("Duck is squeaking");
        }
    }
    public class MuteQuack : QuackBehavior
    {
        public void quack()
        {
            Console.WriteLine("Do nothing");
        }
    }

    public class MallarDuck : Duck
    {
        public MallarDuck() 
        {
            flyBehavior = new FlyWithWings();
            quackBehavior = new Quack();
        }
        public override void display()
        {
            Console.WriteLine("This is a real Mallard duck");
        }
    }
}

Usage:

        static void CallStrategy()
        {
            MallarDuck duck = new MallarDuck();

            //Perform the default behaviors assigned in construct
            duck.performFly();
            duck.performQuack();

            //Change the hehaviors during runtime
            duck.setFlyBehavior(new FlyNoWay());
            duck.setQuackBehavior(new MuteQuack());

            duck.performFly();
            duck.performQuack();
        }

Class Diagram: