C# Adapter Design Pattern

A visualization of the classes and objects participating in this pattern.

The classes and objects participating in this pattern include:

• Target   (ChemicalCompound)
  • defines the domain-specific interface that Client uses.
• Adapter   (Compound)
  • adapts the interface Adaptee to the Target interface.
• Adaptee   (ChemicalDatabank)
  • defines an existing interface that needs adapting.
• Client   (AdapterApp)
  • collaborates with objects conforming to the Target interface.

This structural code demonstrates the Adapter pattern which maps the interface of one class onto another so that they can work together. These incompatible classes may come from different libraries or frameworks.

using System;
namespace Adapter.Structural
{
    /// <summary>
    /// Adapter Design Pattern
    /// </summary>
    public class Program
    {
        public static void Main(string[] args)
        {
            // Create adapter and place a request
            Target target = new Adapter();
            target.Request();
            // Wait for user
            Console.ReadKey();
        }
    }
    /// <summary>
    /// The 'Target' class
    /// </summary>
    public class Target
    {
        public virtual void Request()
        {
            Console.WriteLine("Called Target Request()");
        }
    }
    /// <summary>
    /// The 'Adapter' class
    /// </summary>
    public class Adapter : Target
    {
        private Adaptee adaptee = new Adaptee();
        public override void Request()
        {
            // Possibly do some other work
            // and then call SpecificRequest
            adaptee.SpecificRequest();
        }
    }
    /// <summary>
    /// The 'Adaptee' class
    /// </summary>
    public class Adaptee
    {
        public void SpecificRequest()
        {
            Console.WriteLine("Called SpecificRequest()");
        }
    }
}

Output

This real-world code demonstrates the use of a legacy chemical databank. Chemical compound objects access the databank through an Adapter interface.

using System;
namespace Adapter.RealWorld
{
    /// <summary>
    /// Adapter Design Pattern
    /// </summary>
    public class Program
    {
        public static void Main(string[] args)
        {
            // Non-adapted chemical compound
            Compound unknown = new Compound();
            unknown.Display();
            // Adapted chemical compounds
            Compound water = new RichCompound("Water");
            water.Display();
            Compound benzene = new RichCompound("Benzene");
            benzene.Display();
            Compound ethanol = new RichCompound("Ethanol");
            ethanol.Display();
            // Wait for user
            Console.ReadKey();
        }
    }
    /// <summary>
    /// The 'Target' class
    /// </summary>
    public class Compound
    {
        protected float boilingPoint;
        protected float meltingPoint;
        protected double molecularWeight;
        protected string molecularFormula;
        public virtual void Display()
        {
            Console.WriteLine("\nCompound: Unknown ------ ");
        }
    }
    /// <summary>
    /// The 'Adapter' class
    /// </summary>
    public class RichCompound : Compound
    {
        private string chemical;
        private ChemicalDatabank bank;
        // Constructor
        public RichCompound(string chemical)
        {
            this.chemical = chemical;
        }
        public override void Display()
        {
            // The Adaptee
            bank = new ChemicalDatabank();
            boilingPoint = bank.GetCriticalPoint(chemical, "B");
            meltingPoint = bank.GetCriticalPoint(chemical, "M");
            molecularWeight = bank.GetMolecularWeight(chemical);
            molecularFormula = bank.GetMolecularStructure(chemical);
            Console.WriteLine("\nCompound: {0} ------ ", chemical);
            Console.WriteLine(" Formula: {0}", molecularFormula);
            Console.WriteLine(" Weight : {0}", molecularWeight);
            Console.WriteLine(" Melting Pt: {0}", meltingPoint);
            Console.WriteLine(" Boiling Pt: {0}", boilingPoint);
        }
    }
    /// <summary>
    /// The 'Adaptee' class
    /// </summary>
    public class ChemicalDatabank
    {
        // The databank 'legacy API'
        public float GetCriticalPoint(string compound, string point)
        {
            // Melting Point
            if (point == "M")
            {
                switch (compound.ToLower())
                {
                    case "water": return 0.0f;
                    case "benzene": return 5.5f;
                    case "ethanol": return -114.1f;
                    default: return 0f;
                }
            }
            // Boiling Point
            else
            {
                switch (compound.ToLower())
                {
                    case "water": return 100.0f;
                    case "benzene": return 80.1f;
                    case "ethanol": return 78.3f;
                    default: return 0f;
                }
            }
        }
        public string GetMolecularStructure(string compound)
        {
            switch (compound.ToLower())
            {
                case "water": return "H20";
                case "benzene": return "C6H6";
                case "ethanol": return "C2H5OH";
                default: return "";
            }
        }
        public double GetMolecularWeight(string compound)
        {
            switch (compound.ToLower())
            {
                case "water": return 18.015;
                case "benzene": return 78.1134;
                case "ethanol": return 46.0688;
                default: return 0d;
            }
        }
    }
}

Output

The .NET optimized code demonstrates the same code as above but uses more modern C# and .NET features.

Here is an elegant C# Adapter solution.

namespace Adapter.NetOptimized;
using static System.Console;
/// <summary>
/// Adapter Design Pattern
/// </summary>
public class Program
{
    public static void Main()
    {
        // Non-adapted chemical compound 
        var unknown = new Compound();
        unknown.Display();
        // Adapted chemical compounds
        var water = new RichCompound(Chemical.Water);
        water.Display();
        var benzene = new RichCompound(Chemical.Benzene);
        benzene.Display();
        var ethanol = new RichCompound(Chemical.Ethanol);
        ethanol.Display();
        // Wait for user
        ReadKey();
    }
}
/// <summary>
/// The 'Target' class
/// </summary>
public class Compound
{
    public Chemical Chemical { get; protected set; }
    public float BoilingPoint { get; protected set; }
    public float MeltingPoint { get; protected set; }
    public double MolecularWeight { get; protected set; }
    public string? MolecularFormula { get; protected set; }
    public virtual void Display()
    {
        WriteLine("\nCompound: Unknown ------ ");
    }
}
/// <summary>
/// The 'Adapter' class
/// </summary>
public class RichCompound : Compound
{
    private readonly ChemicalDatabank bank = new();
    // Constructor
    public RichCompound(Chemical chemical)
    {
        Chemical = chemical;
    }
    public override void Display()
    {
        // Adaptee request methods
        BoilingPoint = bank.GetCriticalPoint(Chemical, State.Boiling);
        MeltingPoint = bank.GetCriticalPoint(Chemical, State.Melting);
        MolecularWeight = bank.GetMolecularWeight(Chemical);
        MolecularFormula = bank.GetMolecularStructure(Chemical);
        WriteLine($"\nCompound: { Chemical} ------ ");
        WriteLine($" Formula: {MolecularFormula}");
        WriteLine($" Weight : {MolecularWeight}");
        WriteLine($" Melting Pt: {MeltingPoint}");
        WriteLine($" Boiling Pt: {BoilingPoint}");
    }
}
/// <summary>
/// The 'Adaptee' class
/// </summary>
public class ChemicalDatabank
{
    // The databank 'legacy API'
    public float GetCriticalPoint(Chemical compound, State point)
    {
        // Melting Point
        if (point == State.Melting)
        {
            return compound switch
            {
                Chemical.Water => 0.0f,
                Chemical.Benzene => 5.5f,
                Chemical.Ethanol => -114.1f,
                _ => 0f,
            };
        }
        // Boiling Point
        else
        {
            return compound switch
            {
                Chemical.Water => 100.0f,
                Chemical.Benzene => 80.1f,
                Chemical.Ethanol => 78.3f,
                _ => 0f,
            };
        }
    }
    public string GetMolecularStructure(Chemical compound)
    {
        return compound switch
        {
            Chemical.Water => "H20",
            Chemical.Benzene => "C6H6",
            Chemical.Ethanol => "C2H5OH",
            _ => "",
        };
    }
    public double GetMolecularWeight(Chemical compound)
    {
        return compound switch
        {
            Chemical.Water => 18.015d,
            Chemical.Benzene => 78.1134d,
            Chemical.Ethanol => 46.0688d,
            _ => 0d
        };
    }
}
/// <summary>
/// Chemical enumeration
/// </summary>
public enum Chemical
{
    Water,
    Benzene,
    Ethanol
}
/// <summary>
/// State enumeration
/// </summary>
public enum State
{
    Boiling,
    Melting
}

Output