【C#】初心者必見！インターフェースの使いどころを徹底解説

public interface IExample
{
    void DoSomething();
    int Value { get; set; }
}

// インターフェース
public interface IAnimal
{
    void Speak();
}

// 抽象クラス
public abstract class Animal
{
    public abstract void Speak();

    public void Eat()
    {
        Console.WriteLine("Eating...");
    }
}

public interface IShape
{
    double GetArea(); // 面積を計算するメソッド
    string Name { get; } // 図形の名前
}

public class Rectangle : IShape
{
    public double Width { get; set; }
    public double Height { get; set; }
    public string Name => "Rectangle";

    public double GetArea()
    {
        return Width * Height;
    }
}

public class Circle : IShape
{
    public double Radius { get; set; }
    public string Name => "Circle";

    public double GetArea()
    {
        return Math.PI * Radius * Radius;
    }
}

IShape[] shapes = new IShape[]
{
    new Rectangle { Width = 5, Height = 10 },
    new Circle { Radius = 3 }
};

foreach (var shape in shapes)
{
    Console.WriteLine($"{shape.Name}: Area = {shape.GetArea()}");
}

public interface IDevice
{
    void Start();
    
    void Stop()
    {
        Console.WriteLine("Device stopped.");
    }
}

public class Printer : IDevice
{
    public void Start()
    {
        Console.WriteLine("Printer started.");
    }
}

IDevice device = new Printer();
device.Start(); // Output: Printer started.
device.Stop();  // Output: Device stopped.

public interface IVehicle
{
    void Drive();
}

public interface IElectricVehicle : IVehicle
{
    void ChargeBattery();
}

public class ElectricCar : IElectricVehicle
{
    public void Drive()
    {
        Console.WriteLine("Driving electric car.");
    }

    public void ChargeBattery()
    {
        Console.WriteLine("Charging battery.");
    }
}

IElectricVehicle tesla = new ElectricCar();
tesla.Drive();          // Output: Driving electric car.
tesla.ChargeBattery();  // Output: Charging battery.

IVehicle vehicle = new ElectricCar();
vehicle.Drive(); // Output: Driving electric car.

public interface ILogger
{
    void Log(string message);
}

public class ConsoleLogger : ILogger
{
    public void Log(string message)
    {
        Console.WriteLine($"[Console] {message}");
    }
}

public class FileLogger : ILogger
{
    public void Log(string message)
    {
        System.IO.File.AppendAllText("log.txt", message + "\n");
    }
}

public class Application
{
    private readonly ILogger _logger;

    public Application(ILogger logger)
    {
        _logger = logger;
    }

    public void Run()
    {
        _logger.Log("Application is running.");
    }
}

class Program
{
    static void Main()
    {
        ILogger logger = new ConsoleLogger(); // ConsoleLogger を使用
        var app = new Application(logger);
        app.Run();
    }
}

public interface IPlugin
{
    string Name { get; }
    void Execute();
}

public class PluginA : IPlugin
{
    public string Name => "Plugin A";
    public void Execute()
    {
        Console.WriteLine("Executing Plugin A");
    }
}

public class PluginB : IPlugin
{
    public string Name => "Plugin B";
    public void Execute()
    {
        Console.WriteLine("Executing Plugin B");
    }
}

class Program
{
    static void Main()
    {
        var plugins = LoadPlugins();
        foreach (var plugin in plugins)
        {
            Console.WriteLine($"Running {plugin.Name}");
            plugin.Execute();
        }
    }

    static List<IPlugin> LoadPlugins()
    {
        // プラグインをアセンブリからロードする（例: DLLファイル）
        return new List<IPlugin>
        {
            new PluginA(),
            new PluginB()
        };
    }
}

public interface IDatabase
{
    void Connect();
}

public abstract class DatabaseBase : IDatabase
{
    public abstract void Connect();

    public void Log(string message)
    {
        Console.WriteLine($"Log: {message}");
    }
}

public class SqlDatabase : DatabaseBase
{
    public override void Connect()
    {
        Console.WriteLine("Connecting to SQL Database.");
    }
}

IDatabase database = new SqlDatabase();
database.Connect(); // Output: Connecting to SQL Database.