新手请问一个多线程中同步的有关问题

class Demo implements Runnable
{
    private int ticket = 10 ;
    public synchronized void fun()
    {
            if (this.ticket >0)
            {
            
                try
                {
                    Thread.sleep(100);
                }
                catch (Exception e)
                {

                }
                System.out.println(Thread.currentThread().getName()+"-->卖票:"+this.ticket--);
            }    
    }
    public void run()
    {
        while(ticket>0)
        {
            this.fun();
        }
    }

}
public class ThreadDemo07
{
    public static void main(String[] args)
    {
        Demo d = new Demo();
        Thread t1 = new Thread(d,"A");
        Thread t2 = new Thread(d,"B");
        Thread t3 = new Thread(d,"C");

        t1.start();
        t2.start();
        t3.start();


    }
}