Strategy

• Defines a family of algorithms, encapsulate each one, and make them interchangeable.

Classical Structure

Scenario

• Build a class for storing image after compressing and applying filter

Problem

• Violates SRP
• Violates OCP

public class ImageStorage
{
    private string compressor;
    private string filter;

    public ImageStorage(string compressor, string filter)
    {
        this.compressor = compressor;
        this.filter = filter;
    }

    public void Store()
    {
        if(compressor == "JPG")
            Console.WriteLine("Compressing image using JPG");
        else if(compressor == "PNG")
            Console.WriteLine("Compressing image using PNG");

        if (filter == "BW")
            Console.WriteLine("Apply filter BW");
        else if (filter == "HC")
            Console.WriteLine("Apply high contrast");
    }
}

Solution

public interface ICompressor
{
    void Compress(string fileName);
}
public class JPGCompressor : ICompressor
{
    public void Compress(string fileName)
    {
        Console.WriteLine("Compressing image");
    }
}
public interface IFilter
{
    void Apply(string fileName);
}
public class BlackAndWhiteFilter : IFilter
{
    public void Apply(string fileName)
    {
        Console.WriteLine("Applying BW filter");
    }
}
public class ImageStorage
{
    private ICompressor compressor;
    private IFilter filter;

    public ImageStorage(ICompressor compressor, IFilter filter)
    {
        this.compressor = compressor;
        this.filter = filter;
    }

    public void Store(string fileName)
    {
        compressor.Compress(fileName);

        filter.Apply(fileName);
    }
}
public class Program
{
    static void Main(string[] args)
    {
        var imageStorage = new ImageStorage(new JPGCompressor(), new BlackAndWhiteFilter());
        imageStorage.Store("a");
    }
}

Example Structure

Example Code