线程同步问题

package zxd.work622;

public class TestAccount extends Thread {
    private Account a = new Account();

    public void run() {
        for (int i = 0; i < 10; i++) {
            this.makeWithDraw(100);
            if (a.getBlance() < 0) {
                System.out.println("余额透支");
            }
        }
    }
    private synchronized void makeWithDraw(int money) {//线程同步
        synchronized (a) {　　//线程同步
            if (money <= a.getBlance()) {
                System.out.println("准备取款");
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                a.withDraw(money);
                System.out.println(Thread.currentThread().getName() + "取了"
                        + money + "余额：" + a.getBlance());
            } else {
                System.out.println("余额不足：" + Thread.currentThread().getName()
                        + "取款失败");
            }
        }
    }
    public static void main(String[] args) {
        TestAccount t = new TestAccount();
        Thread one = new Thread(t);
        Thread two = new Thread(t);
        one.setName("张三");
        two.setName("李四");
        one.start();
        two.start();


    }
}