<div style="display:flex; max-width:100%; padding-bottom:16px"> <div style="flex-shrink:0; padding-top:6px; padding-right:16px;"> <img style="width:50px; height:50px; border-radius:50%;" src="http://third.qlogo.cn/ek_app/AQVJKMtqeFCGNEZqicOj7qb7mnpcJiaZNlEOf0iasx2DicuEycbIG9cQktWUBxWR1dFWfLMI2Ilt/100"> </div> <div style="flex-grow:1; overflow:auto;"> <span style="line-height:32px"> 廖雪峰 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 98 98" style="width:24px;height:24px"><path fill-rule="evenodd" clip-rule="evenodd" d="M48.854 0C21.839 0 0 22 0 49.217c0 21.756 13.993 40.172 33.405 46.69 2.427.49 3.316-1.059 3.316-2.362 0-1.141-.08-5.052-.08-9.127-13.59 2.934-16.42-5.867-16.42-5.867-2.184-5.704-5.42-7.17-5.42-7.17-4.448-3.015.324-3.015.324-3.015 4.934.326 7.523 5.052 7.523 5.052 4.367 7.496 11.404 5.378 14.235 4.074.404-3.178 1.699-5.378 3.074-6.6-10.839-1.141-22.243-5.378-22.243-24.283 0-5.378 1.94-9.778 5.014-13.2-.485-1.222-2.184-6.275.486-13.038 0 0 4.125-1.304 13.426 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从Java 5开始，引入了一个高级的处理并发的包，它提供了大量更高级的并发功能，能大大简化多线程程序的编写。
我们知道Java语言直接提供了关键字用于加锁，但这种锁一是很重，二是获取时必须一直等待，没有额外的尝试机制。
包提供的用于替代加锁，我们来看一下传统的代码：
如果用替代，可以把代码改造为：
因为是Java语言层面提供的语法，所以我们不需要考虑异常，而是Java代码实现的锁，我们就必须先获取锁，然后在中正确释放锁。
顾名思义，是可重入锁，它和一样，一个线程可以多次获取同一个锁。
和不同的是，可以尝试获取锁：
上述代码在尝试获取锁的时候，最多等待1秒。如果1秒后仍未获取到锁，返回，程序就可以做一些额外处理，而不是无限等待下去。
所以，使用比直接使用更安全，线程在失败的时候不会导致死锁。
可以替代进行同步；
获取锁更安全；
必须先获取到锁，再进入代码块，最后使用保证释放锁；
可以使用尝试获取锁。
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