有关Java线程里同步锁的问题（求助）

代码是三个窗口售票

这段代码线程是安全的，它和第二个不安全有什么区别么，之不不过是判定条件改变，两段代码同步监视器（锁）在程序运行中都是唯一的。
第一段代码：

public class ThreadWindons implements Runnable{
    private int count = 100;
    Object obj = new Object();
    public void run(){
        while(true){//这里为true，此时线程安全
            synchronized (obj) {//同步锁，给共享资源上锁
                if(count > 0){

                    try {
                        Thread.sleep(100);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(Thread.currentThread().getName() + "售出" + count + "号票");
                    count--;
                    }
                else{
                    break;
                }
            }
        }
    }

}
class ThreadTest{
    public static void main(String[] args){
        ThreadWindons t1 = new ThreadWindons();
        Thread w1 = new Thread(t1);
        Thread w2 = new Thread(t1);
        Thread w3 = new Thread(t1);
        w1.setName("1号窗口");
        w2.setName("2号窗口");
        w3.setName("3号窗口");
        w1.start();
        w2.start();
        w3.start();
    }
}

结果：

无错票
第二段代码：

public class ThreadWindons implements Runnable{
    private int count = 100;
    Object obj = new Object();
    public void run(){
        while(count > 0){
            synchronized (obj) {//同步锁，给共享资源上锁
                try {
                    Thread.sleep(100);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName() + "售出" + count + "号票");
                count--;
            }
        }
    }

}
class ThreadTest{
    public static void main(String[] args){
        ThreadWindons t1 = new ThreadWindons();
        Thread w1 = new Thread(t1);
        Thread w2 = new Thread(t1);
        Thread w3 = new Thread(t1);
        w1.setName("1号窗口");
        w2.setName("2号窗口");
        w3.setName("3号窗口");
        w1.start();
        w2.start();
        w3.start();
    }
}

结果：

出现错票