java 使用同步代码块解决卖票为负的问题

class MyThread implements Runnable{
    private int ticket=5;
    public void run(){
        for(int i=0;i<100;i++){
            synchronized (this){
                if(ticket>0){
                    try{
                        Thread.sleep(300);
                    }catch(InterruptedException e){
                        e.printStackTrace();
                    }
                    System.out.println("卖票：ticket="+ticket--);
                }
            }
        }
    }
};
public class SyncDemo1 {
    public static void main(String[] args) {
        MyThread mt=new MyThread();
        Thread t1=new Thread(mt);
        Thread t2=new Thread(mt);
        Thread t3=new Thread(mt);
        t1.start();
        t2.start();
        t3.start();
    }
}