Program.cs

using System;

namespace DependencyInjection
{
    public interface ISaw{
        void Cut();
    }

    public interface IHammer
    {
        void Nail();
    }

    public class Saw : ISaw
    {
        public void Cut()
        {
            Console.WriteLine("Using saw to cut wood.");
        }
    }

    public class Hammer : IHammer
    {
        public void Nail()
        {
            Console.WriteLine("Using hammer to nail wood.");
        }
    }
    public class ElectricSaw : ISaw
    {
        public void Cut()
        {
            Console.WriteLine("Using electric saw to cut wood faster.");
        }
    }

    public class RubberHammer : IHammer
    {
        public void Nail()
        {
            Console.WriteLine("Using rubber hammer, gentler on surfaces.");
        }
    }
    public class Builder
    {
        private readonly ISaw _saw;
        private readonly IHammer _hammer;

        public Builder(ISaw saw, IHammer hammer)
        {
            _saw = saw;
            _hammer = hammer;
        }

        public void Build()
        {
            _saw.Cut();
            _hammer.Nail();
            Console.WriteLine("Building the house.");
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            ISaw saw = new Saw();
            IHammer hammer = new Hammer();

            Builder builder = new Builder(saw, hammer);
            Console.WriteLine("Building with original tools:");
            builder.Build();

            Console.WriteLine();
            ISaw electricSaw = new ElectricSaw();
            IHammer rubberHammer = new RubberHammer();

            Builder builderWithNewTools = new Builder(electricSaw, rubberHammer);
            Console.WriteLine("Building with swapped (alternative) tools:");
            builderWithNewTools.Build();

            Console.WriteLine("Done!");
        }
    }
}