关于JAVA线程的问题

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解决时间 2021-05-09 17:42

提问者网友：眉目添风霜
2021-05-09 04:37

class ThreadDemo1{
public static void main(String [] args) { TestThread t = new TestThread(); new Thread(t).start(); new Thread(t).start(); new Thread(t).start(); new Thread(t).start(); }}class TestThread implements Runnable{ String str = new String(""); int ticket =100; public void run() { synchronized(str) { while(true) { if(ticket>0) { try{ Thread.sleep(10);} catch(Exception e) { } System.out.println(Thread.currentThread().getName()+"is saling"+ticket--); } } } }}我也不知道怎么说这个问题，就是书上运行结果是：Thread-1 is saling tickets 100Thread-2 is saling tickets 99Thread-3 is saling tickets 98Thread-4 is saling tickets 97Thread-1 is saling tickets 96Thread-2 is saling tickets 95Thread-3 is saling tickets 94Thread-4 is saling tickets 93 . . . . Thread-1 is saling tickets 4Thread-2 is saling tickets 3Thread-3 is saling tickets 2Thread-4 is saling tickets 1而我的执行结果（多次基本上都是这个结果）：Thread-0 is saling tickets 100Thread-0 is saling tickets 99Thread-0 is saling tickets 98Thread-0 is saling tickets 97Thread-0 is saling tickets 96Thread-0 is saling tickets 95Thread-0 is saling tickets 94Thread-0 is saling tickets 93 . . . . . . . .Thread-0 is saling tickets 4Thread-0 is saling tickets 3Thread-0 is saling tickets 2Thread-0 is saling tickets 1有几点疑问:(1)书上的是从Thread-1开始的，而我的却是从Thread-0开始的，不知道这跟系统或者配置有关吗？(2)书上这个是交替运行，我这个却不是，Thread-0这个进程一直不让出cpu，不懂为什么？？？(3)后来猜测是不是由于处理机,cpu等等都比书上那时候快得多，于是把sleep时间调到了sleep(19)，运行多次虽然还是多次出现：Thread-0 is saling tickets 100Thread-0 is saling tickets 99Thread-0 is saling tickets 98Thread-0 is saling tickets 97Thread-0 is saling tickets 96Thread-0 is saling tickets 95Thread-0 is saling tickets 94Thread-0 is saling tickets 93 . . . . Thread-0 is saling tickets 4Thread-0 is saling tickets 3Thread-0 is saling tickets 2Thread-0 is saling tickets 1这个结果，但也偶尔出现了如下结果：Thread-0 is saling tickets 100Thread-0 is saling tickets 99Thread-0 is saling tickets 98Thread-0 is saling tickets 97Thread-0 is saling tickets 96 . . . . Thread-0 is saling tickets 73Thread-3 is saling tickets 72Thread-3 is saling tickets 71Thread-3 is saling tickets 70Thread-3 is saling tickets 69Thread-3 is saling tickets 68Thread-3 is saling tickets 67Thread-3 is saling tickets 66Thread-1 is saling tickets 65Thread-1 is saling tickets 64Thread-1 is saling tickets 63 . . . .Thread-1 is saling tickets 1虽然这次出现了其它进程，应该算是交替执行吧？？可是还是不是书上那种，顺序执行！！~（4）sleep后一定会出现cpu切换进程吗？或者说cpu不一定切换，而在那个进程那里等他睡眠结束？

最佳答案

五星知识达人网友：动情书生
2021-05-09 04:51

书上是错的

线程名默认是从Thread-0开始

并且运行的是同一个对象实例，只要有一个实例调用了synchronized(str)，在没有释放之前，其它实例不可能会被执行，不管里面sleep了多少秒，只要锁还没有结束，其它实例想再调用str的锁，那是一定要等待的。

你说的sleep的值调大一点，就会出现其它情况，那不可能，不管多少秒结果都是一定的。你可以在if后面那里加个else，会看到其它线程其实也进入循环了，只是那时候的ticket已经是小于0，所以它们都没有输出

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