C# 使用17方法编写Hello World程序（语法深度）

. A Beginners Hello World   //初学者
public class HelloWorld
{ 
  public static void Main()
  {
    System.Console.WriteLine("HELLO WORLD");
  }
}
. Slightly improved version   //略有提高  
using System;  //（就这？会用命名空间？）
public class HelloWorld
{ 
  public static void Main()
  {
    Console.WriteLine("HELLO WORLD");
  }
}
. Command Line Arguments   //命令行参数
using System;
public class HelloWorld
{ 
  public static void Main(string[] args)   //会传参数了
  {
    Console.WriteLine(args[0]);
  }
}
. From Constructor    //构造函数
using System;
public class HelloWorld
{ 
  public HelloWorld()
  {
    Console.WriteLine("HELLO WORLD");
  }
  public static void Main() 
  {
    HelloWorld hw = new HelloWorld();  //会用类了？构造？
  }
}
. More OO
using System;
public class HelloWorld
{ 
  public void helloWorld()
  {
    Console.WriteLine("HELLO WORLD");
  }
  public static void Main() 
  {
    HelloWorld hw = new HelloWorld();
    hw.HelloWorld();   //更进一步的面向对象？会用方法了？
  }
}
. From another class  //调用另一个类
using System;
public class HelloWorld
{ 
  public static void Main()
  {
    HelloWorldHelperClass hwh = new HelloWorldHelperClass();   //类里调用其它类？
    hwh.writeHelloWorld(); 
  }
}
public class HelloWorldHelperClass
{ 
  public void writeHelloWorld() 
  {
    Console.WriteLine("Hello World"); 
  }
} 
. Inheritance  //继承
abstract class HelloWorldBase  //抽象类
{
    public abstract void writeHelloWorld();
}
class HelloWorld : HelloWorldBase  //继承----不得不严肃起来了，能抽象的已经可以做系统架构设计了！
{
    public override void writeHelloWorld()
    {
        Console.WriteLine("Hello World");
        Console.ReadLine();
    }
}
class HelloWorldImp
{
    static void Main()
    {
        HelloWorldBase hwb = new HelloWorld();
        hwb.writeHelloWorld();
    }
}
. Static Constructor //静态构造函数
using System;
public class HelloWorld
{ 
  private static string strHelloWorld;
  static HelloWorld()    //静态构造
  {
    strHelloWorld = "Hello World";
  }
  void writeHelloWorld()
  {
    Console.WriteLine(strHelloWorld);    }
  public static void Main() 
  {
    HelloWorld hw = new HelloWorld();   //需要吗？
    hw.writeHelloWorld();   //平常我会觉得很可笑----居然写得这么啰嗦

  }
}
. Exception Handling  //异常处理
using System;
public class HelloWorld
{ 
  public static void Main(string[] args)
  {
    try
    {
      Console.WriteLine(args[0]);
    }
    catch(IndexOutOfRangeException e)   //会用异常处理了,但如何更好回收资源呢？异常接下来应该是资源回收啊？我以前也犯这种毛病，GC应该怎么更好使用，我到现在还不是很纯熟
    {
      Console.WriteLine(e.ToString());
    }
  }
. Creating a DLL and using it in an application   //做组件吗？
using System;
namespace HelloLibrary
{
  public class HelloMessage
  {
    public string Message
    {
      get
      {
        return "Hello, World!!!";
      }
    }
  } 
}
 
//-------------------------
using System;
using HelloLibrary;
namespace HelloApplication
{
  class HelloApp
  {
    public static void Main(string[] args)
    {
      HelloMessage m = new HelloMessage();
    }
  }
}
. Using Property   //实用属性
using System;
public class HelloWorld
{
    public string strHelloWorld
    {
        get   //会用属性了
        {
            return "Hello World";
        }
    }
    public static void Main()
    {
        HelloWorld hw = new HelloWorld();
        Console.WriteLine(hw.strHelloWorld);
    }
}
. Using Delegates    //委托！
using System;

class HelloWorld
{
    delegate void SimpleDelegate();//定义委托

    static void writeHelloWorld()
    {
        Console.WriteLine("HelloWorld");
    }

    static void Main()
    {
        SimpleDelegate d = new SimpleDelegate(writeHelloWorld);  //委托？！？！
        d();   //语法的确这么写，但含义无法理解;因为实在体会不出好处来
    }
}
. Using Attributes    //我不会！补习去！
#define DEBUGGING
using System;
using System.Diagnostics;
public class HelloWorld : Attribute
{
    [Conditional("DEBUGGING")]
    public void writeHelloWorld()
    {
        Console.WriteLine("Hello World");
        Console.ReadLine();
    }
    public static void Main()
    {
        HelloWorld hw = new HelloWorld();
        hw.writeHelloWorld();
    }
}
. Using Interfaces   //接口
using System;
interface IHelloWorld
{
    void writeHelloWorld();
}
public class HelloWorld : IHelloWorld
{
    public void writeHelloWorld()
    {
        Console.WriteLine("Hello World");
    }
    public static void Main()
    {
        HelloWorld hw = new HelloWorld();
        hw.writeHelloWorld();
    }
}
. Dynamic Hello World  //Again
using System;
using System.Reflection;
namespace HelloWorldNS
{
  public class HelloWorld
  { 
    public string writeHelloWorld()
    {
      return "HelloWorld";
    }
    public static void Main(string[] args) 
    {
      Type hw = Type.GetType(args[0]);
      // Instantiating a class dynamically
      object[] nctorParams = new object[] {};
      object nobj = Activator.CreateInstance(hw, 
               nctorParams);
      // Invoking a method
      object[] nmthdParams = new object[] {};
      string strHelloWorld = (string) hw.InvokeMember(
              "writeHelloWorld", BindingFlags.Default | 
              BindingFlags.InvokeMethod, null, 
              nobj, nmthdParams);
      Console.WriteLine(strHelloWorld);
    }
  }
. Unsafe Hello World   //Unsafe
using System;
public class HelloWorld
{
    unsafe public void writeHelloWorld(char[] chrArray)
    {
        fixed (char* parr = chrArray)
        {
            char* pch = parr;
            for (int i = 0; i < chrArray.Length; i++)
                Console.Write(*(pch + i));
        }
    }
    public static void Main()
    {
        HelloWorld hw = new HelloWorld();
        char[] chrHelloWorld = new char[] { 'H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd' };
        hw.writeHelloWorld(chrHelloWorld);
    }
. Using InteropServices
using System;
using System.Runtime.InteropServices;
class Class1
{  //COM ,  API接口  我以前就这么低俗地理解.    其实工具会帮你生成
    [DllImport("kernel32")]
    private static extern int Beep(int dwFreq, int dwDuration);
    static void Main(string[] args)
    {
        Console.WriteLine("Hello World");
        Beep(1000, 2000);
    }}