principlecsharpMinor

Strategy Pattern

Submitted by: @import:stackexchange-codereview·Mar 10, 2026·

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patternstrategystackoverflow

Problem

I am working on going through "Head First Design Patterns" and I am trying to properly convert the Java code into C#. Here is what I have. Can you tell me if this is a good implementation/conversion so far?

```
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Duck
{
public abstract class Duck
{
public FlyBehavior flyBehavior;
public QuackBehavior quackBehavior;
public Duck(){

}

public abstract void display();

public void performFly()
{
flyBehavior.fly();
}

public void performQuack()
{
quackBehavior.quack();
}

public void swim()
{
Console.WriteLine("All ducks float, even decoys!");
}
}

public interface FlyBehavior
{
void fly();
}

public class FlyWithWings : FlyBehavior
{
public void fly()
{
Console.WriteLine("I'm flying!");
}
}

public class FlyNoWay : FlyBehavior
{
public void fly()
{
Console.WriteLine("I can't fly!");
}
}

public interface QuackBehavior
{
void quack();
}

public class Quack : QuackBehavior
{
public void quack()
{
Console.WriteLine("Quack");
}
}

public class MuteQuack : QuackBehavior
{
public void quack()
{
Console.WriteLine(">");
}
}

public class Squeak : QuackBehavior
{
public void quack()
{
Console.WriteLine("Squeak");
}
}

public class MallardDuck : Duck
{
public MallardDuck()
{
quackBehavior = new Quack();
flyBehavior = new FlyWithWings();
}

public override void display()
{
Console.WriteLine("I'm a real Mallard duck");
}
}

public class MiniDuckSimulator

Solution

public fields are a bit of a no-no since that violates encapsulation. So I've changed the fields to private readonly and inject those dependencies via the constructor. Speaking of constructor, I made it protected as a public constructor on an abstract class doesn't make much sense. Also, make note of C# naming conventions which PascalCase's methods and that interfaces should start with "I":

using System;

namespace Duck
{
    public abstract class Duck
    {
        private readonly IFlyBehavior flyBehavior;
        private readonly IQuackBehavior quackBehavior;
        protected Duck(IFlyBehavior flyBehavior, IQuackBehavior quackBehavior)
        {
            this.flyBehavior = flyBehavior;
            this.quackBehavior = quackBehavior;
        }

        public abstract void Display();

        public void PerformFly()
        {
            this.flyBehavior.Fly();
        }

        public void PerformQuack()
        {
            this.quackBehavior.Quack();
        }

        public void Swim()
        {
            Console.WriteLine("All ducks float, even decoys!");
        }
    }

    public interface IFlyBehavior
    {
        void Fly();
    }

    public class FlyWithWings : IFlyBehavior
    {
        public void Fly()
        {
            Console.WriteLine("I'm flying!");
        }
    }

    public class FlyNoWay : IFlyBehavior
    {
        public void Fly()
        {
            Console.WriteLine("I can't fly!");
        }
    }

    public interface IQuackBehavior
    {
        void Quack();
    }

    public class Quack : IQuackBehavior
    {
        public void Quack()
        {
            Console.WriteLine("Quack");
        }
    }

    public class MuteQuack : IQuackBehavior
    {
        public void Quack()
        {
            Console.WriteLine(">");
        }
    }

    public class Squeak : IQuackBehavior
    {
        public void Quack()
        {
            Console.WriteLine("Squeak");
        }
    }

    public class MallardDuck : Duck
    {
        public MallardDuck() : base(new FlyWithWings(), new Quack())
        {
        }

        public override void Display()
        {
            Console.WriteLine("I'm a real Mallard duck");
        }
    }

    public class MiniDuckSimulator
    {
        public static void Main(string[] args)
        {
            Duck mallard = new MallardDuck();
            mallard.PerformQuack();
            mallard.PerformFly();
            Console.ReadLine();
        }
    }
}

Code Snippets

using System;

namespace Duck
{
    public abstract class Duck
    {
        private readonly IFlyBehavior flyBehavior;
        private readonly IQuackBehavior quackBehavior;
        protected Duck(IFlyBehavior flyBehavior, IQuackBehavior quackBehavior)
        {
            this.flyBehavior = flyBehavior;
            this.quackBehavior = quackBehavior;
        }

        public abstract void Display();

        public void PerformFly()
        {
            this.flyBehavior.Fly();
        }

        public void PerformQuack()
        {
            this.quackBehavior.Quack();
        }

        public void Swim()
        {
            Console.WriteLine("All ducks float, even decoys!");
        }
    }

    public interface IFlyBehavior
    {
        void Fly();
    }

    public class FlyWithWings : IFlyBehavior
    {
        public void Fly()
        {
            Console.WriteLine("I'm flying!");
        }
    }

    public class FlyNoWay : IFlyBehavior
    {
        public void Fly()
        {
            Console.WriteLine("I can't fly!");
        }
    }

    public interface IQuackBehavior
    {
        void Quack();
    }

    public class Quack : IQuackBehavior
    {
        public void Quack()
        {
            Console.WriteLine("Quack");
        }
    }

    public class MuteQuack : IQuackBehavior
    {
        public void Quack()
        {
            Console.WriteLine("<<  Silence  >>");
        }
    }

    public class Squeak : IQuackBehavior
    {
        public void Quack()
        {
            Console.WriteLine("Squeak");
        }
    }

    public class MallardDuck : Duck
    {
        public MallardDuck() : base(new FlyWithWings(), new Quack())
        {
        }

        public override void Display()
        {
            Console.WriteLine("I'm a real Mallard duck");
        }
    }

    public class MiniDuckSimulator
    {
        public static void Main(string[] args)
        {
            Duck mallard = new MallardDuck();
            mallard.PerformQuack();
            mallard.PerformFly();
            Console.ReadLine();
        }
    }
}

Context

StackExchange Code Review Q#29384, answer score: 6

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