throw在try中抛出异常，然后用catch捕捉并处理这个异常，同时catch也可以再次抛出这个异常

using System;
public class ThrowTest
{
    static void Main()
    {
        string s = null;
        try
        {
            if (s == null)
            {
                throw new ArgumentNullException();
            }
        }
        catch
        {
            s = "litao";
            Console.WriteLine(s);
        }

        Console.Write("The string s is null"); // not executed
    }
}
//输出：
//litao
//The string s is null请按任意键继续 . . .

 同上：

// throw example
using System;
public class ThrowTest
{
    static void Main()
    {
        string s = null;
        try
        {
            if (s == null)
            {
                throw new ArgumentNullException();
            }
        }
        catch
        {
            s = "litao";
           
            Console.WriteLine(s);
           
            throw ;//利用空throw语句，可以再次把已经捕获的异常抛出。
        }
        
        Console.Write("The string s is null"); // not executed
    }
}

同上

// throw example
using System;
public class ThrowTest
{
    static void Main()
    {
        string s = null;
        try
        {
            if (s == null)
            {
                throw(new ArgumentNullException());
            }
        }
        catch(ArgumentException exc)
        {
            s = "litao";
           
            Console.WriteLine(s);
            throw (exc); //等同throw exc;
            //还等同  throw ;//利用空throw语句，可以再次把已经捕获的异常抛出。
            //Console.WriteLine(exc.Message);
            //Console.WriteLine(exc);
        }
        
        Console.Write("The string s is null"); // not executed
    }
}