求教synchronized在多线程的抢票运用有问题

题目要求解决同步问题，用synchronized解决
可是synchronized放哪呢？
```public class TicketOffice implements Runnable{

private int count = 30;
private int no = 0;
private boolean flag = false;

public void run(){
    while(true){
        synchronized(this){
            if(sale()==false)break;
        }
    }
}
public  boolean sale(){

    if(count==0){
        return false;
    }
    try{
        Thread.sleep(500);
    }catch (InterruptedException e){
        e.printStackTrace();
    }
    System.out.println(Thread.currentThread().getName()+"抢到第"+(++no)+"张票，剩余"+count--+"张");


    if(Thread.currentThread().getName().equals("PFZ")){
        return false;
    }

    return true;
}

}

public class Test {

public static void main(String[] args) {
    TicketOffice r = new TicketOffice();
    Thread Z3 = new Thread(r);
    Z3.setName("Z3");
    Thread L4 = new Thread(r);
    L4.setName("L4");
    Thread PFZ = new Thread(r);
    PFZ.setName("PFZ");

    Z3.start();
    L4.start();
    PFZ.start();


}

}

用synchronized 修饰sale()方法，同一时间只有一个线程能进入该方法。