线程锁中private object lockObj = new object();

namespace LockExample
{
class Account
{
private object lockObj = new object();
int balance; //余额
Random r = new Random();
Form1 form1;
public Account(int initial, Form1 form1)
{
this.form1 = form1;
this.balance = initial;
}

/// <summary>
/// 取款
/// </summary>
/// <param name="amount">取款金额</param>
/// <returns>余额</returns>
private int Withdraw(int amount)
{
if (balance < 0)
form1.AddListBoxItem("余额：" + balance + " 已经为负值了，还想取呵！");
lock (lockObj)
{
if (balance >= amount)
{
string str = Thread.CurrentThread.Name + "取款---";
str += string.Format("取款前余额：{0,-6}取款：{1,-6}", balance, amount);
balance = balance - amount;
str += "取款后余额：" + balance;
form1.AddListBoxItem(str);
return amount;
}
else
return 0;
}
}

/// <summary>
/// 自动取款
/// </summary>
public void DoTransactions()
{
for (int i = 0; i < 100; i++)
{
Withdraw(r.Next(1,100));
}
}
}
}
想问一下，lock (lockObj) 中lockObj具体指的是什么？？是什么对象？怎么没有给引用值啥的？看了很多资料还是不懂