如何在C#中自定义自己的异常

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Runtime.Serialization.Formatters.Binary;
namespace ConsoleApplication3
{
    [Serializable] //声明为可序列化的 因为要写入文件中
    public class PayOverflowException : ApplicationException//由用户程序引发，用于派生自定义的异常类型
    {
        /// <summary>
        /// 默认构造函数
        /// </summary>
        public PayOverflowException() { }

        public PayOverflowException(string message)
        : base(message)
        { }

        public PayOverflowException(string message, Exception inner)
        : base(message, inner)
        { }

        //public PayOverflowException(System.Runtime.Serialization.SerializationInfo info,
        // System.Runtime.Serialization.StreamingContext context)
        // : base(info, context) { }
    }

    internal class Employee
    {
        public int ID { get; set; }

        public string Name { get; set; }

        /// <summary>
        /// current pay
        /// </summary>
        public int CurrPay { get; set; }

        public Employee() { }

        public Employee(int id, string name, int currpay)
        {
            this.ID = id;
            this.Name = name;
            this.CurrPay = currpay;
        }

        /// <summary>
        /// 定义一个GiveBunus的虚方法以供不同的派生类进行重载
        /// </summary>
        /// <param name="amount">奖金额度</param>
        public virtual void GiveBunus(int amount)
        {
            //用一个临时变量记录递增之前的值
            var pay = CurrPay;
            this.CurrPay += amount;
            if (CurrPay > 10000)
            {
                //发生异常,将CurrPay的值进行恢复,
                //并抛出异常,外部程序捕获次异常
                this.CurrPay = pay;
                var ex = new PayOverflowException("The employee‘s max pay should be no more than 10000.");
                throw ex;
            }
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("**** 创建Employee对象，并用try/catch捕获异常 *****");
            var emp = new Employee(10001, "Yilly", 8000);
            try
            {
                emp.GiveBunus(3000);
            }
            catch (PayOverflowException ex)
            {
                Console.WriteLine("异常信息:{0}\n发生于{1}类的{2}方法", ex.Message,
                ex.TargetSite.DeclaringType, ex.TargetSite.Name);
                try
                {
                    var file = new FileStream(@"c:\customerexception.txt", FileMode.Create);
                    //*** 异常信息写入文件中的代码省略...
                    //以序列化方式写入
                    BinaryFormatter bf = new BinaryFormatter();
                    bf.Serialize(file, ex);
                    file.Close();
                    //以字节方式写入
                    //byte[] buffer = System.Text.Encoding.Default.GetBytes(ex.Message);
                    //int leng = 0;
                    //leng = buffer.GetLength(0);
                    //file.Write(buffer, 0, leng);
                    //file.Close();
                }
                catch (Exception ex1)
                {
                    var inner = new PayOverflowException(ex.Message, ex1);
                    throw inner;
                }
            }
        }
    }
}