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);
}}