写了一个简单的Java多线程的例子模拟火车售票，但线程同步后，只有一个线程在卖票了，不知道哪儿出问题了，请高手指出来？谢谢！
//线程类
class SellThread implements Runnable {
int tickets = 100;
public void run() {
synchronized (this) {
while (tickets > 0) {
System.out.println(Thread.currentThread().getName()
+ " sell ticket: " + tickets);
tickets--;
}
}
}
}
//测试类
public class TicketsSystem {
public static void main(String[] args) {
SellThread st = new SellThread();
new Thread(st).start();
new Thread(st).start();
new Thread(st).start();
new Thread(st).start();
}
}
运行的结果是：只有第一个线程在卖票
//线程类
class SellThread implements Runnable {
int tickets = 100;
public void run() {
while(true){
if(tickets>0){
count();
}else{
break;
}
}
}
public void count(){
synchronized(this)
{
System.out.println(Thread.currentThread().getName()
+ " sell ticket: " + tickets);
tickets--;
}
}
}
//测试类
public class TicketsSystem {
public static void main(String[] args) {
SellThread st = new SellThread();
