C#中命名空间的实现

namespace MyApplication.Utilities
{
    public class Helper
    {
        public static void DoSomething()
        {
            Console.WriteLine("Doing something...");
        }
    }
}

// 第一种直接使用
MyApplication.Utilities.Helper.DoSomething();


// 第二中使用关键是： using
using MyApplication.Utilities;
Helper.DoSomething();

namespace MyApplication
{
    namespace Data
    {
        public class DatabaseManager
        {
            public void Connect() { /* ... */ }
        }
    }

    namespace Services
    {
        public class UserService
        {
            public void CreateUser() { /* ... */ }
        }
    }
}

// 文件：Calculator.cs
namespace MyApp.Tools
{
    public class Calculator
    {
        public int Add(int x, int y)
        {
            return x + y;
        }

        public int Subtract(int x, int y)
        {
            return x - y;
        }
    }
}

// 文件：Program.cs
using System;
using MyApp.Tools; // 引入自定义命名空间

public class Program
{
    public static void Main(string[] args)
    {
        Calculator calc = new Calculator();
        
        int sum = calc.Add(10, 5);
        int difference = calc.Subtract(10, 5);

        Console.WriteLine($"Sum: {sum}");           // 输出：Sum: 15
        Console.WriteLine($"Difference: {difference}"); // 输出：Difference: 5
    }
}

// 文件：EmailService.cs
namespace MyApp.Services.Communication
{
    public class EmailService
    {
        public void SendEmail(string to, string subject, string body)
        {
            Console.WriteLine($"Sending email to {to} with subject '{subject}'");
        }
    }
}

// 文件：LoggingService.cs
namespace MyApp.Services.Logging
{
    public class LoggingService
    {
        public void LogInfo(string message)
        {
            Console.WriteLine($"INFO: {message}");
        }
    }
}

// 文件：DatabaseService.cs
namespace MyApp.Services.DataAccess
{
    public class DatabaseService
    {
        public void ConnectToDatabase()
        {
            Console.WriteLine("Connecting to database...");
        }
    }
}

// 文件：Program.cs
using System;
using MyApp.Services.Communication;
using MyApp.Services.Logging;
using MyApp.Services.DataAccess;

public class Program
{
    public static void Main(string[] args)
    {
        EmailService emailService = new EmailService();
        LoggingService loggingService = new LoggingService();
        DatabaseService databaseService = new DatabaseService();

        emailService.SendEmail("example@example.com", "Hello", "This is a test email.");
        loggingService.LogInfo("Email sent successfully.");
        databaseService.ConnectToDatabase();
    }
}