多线程模拟取款

Code
using System;
using System.Threading;
using System.Collections;

namespace MultiThreadLearn
{
    internal class Account
    {
        int balance;
        Random r = new Random();
        internal Account(int initial)
        {
            balance = initial;
        }
        internal int Withdraw(int amount)
        {
            try
            {
                if (balance < 0)
                {
                    throw new Exception("Negative Balance");
                }
                lock (this) //如果没有lock，可能会出现负值
                {
                    Console.WriteLine("可用余额：" + balance);
                    if (balance >= amount)
                    {
                        balance = balance - amount;

                        Console.WriteLine("你已经取了:" + amount + ",可用余额为:" + balance + "。交易成功！");
                        Console.WriteLine();
                        return amount;
                    }
                    else
                    {
                        Console.WriteLine("你要取" + amount + "元，但是你的可用余额为" + balance + "。交易失败！");
                        Console.WriteLine();
                        return 0;
                    }
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
                return 0;
            }
        }
        internal void DoTransactions()
        {
            for (int i = 0; i < 2; i++) //每个线程取两次款
            {
                int ri =r.Next(100,200);
                Console.WriteLine("Current Thread:" + Thread.CurrentThread.Name);
                Console.WriteLine("第"+(i+1)+"次交易");
                Console.WriteLine("要取的金额是："+ri);
                Withdraw(ri);
            }
        }
    }
    internal class Test
    {
        static internal Thread[] threads = new Thread[10];
        public static void Main2()
        {
            Account acc = new Account(700); //如果在初始化金额时，传了负值，会抛出异常，并输出
            for (int i = 0; i < 3; i++)
            {
                Thread t = new Thread(new ThreadStart(acc.DoTransactions));
                threads[i] = t;
            }
            threads[1].Priority = ThreadPriority.Highest;//如果不设，第一个输出的是线程0
            for (int i = 0; i < 3; i++)
            {
                threads[i].Name = i.ToString();
            }
            for (int i = 0; i < 3; i++)
            {
                threads[i].Start();
            }
            Console.ReadLine();
        }
    }
}