<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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d="M90.461 40.316a26.753 26.753 0 0 1-7.702 2.109 13.445 13.445 0 0 0 5.897-7.417 26.843 26.843 0 0 1-8.515 3.253 13.396 13.396 0 0 0-9.79-4.233c-7.404 0-13.409 6.005-13.409 13.409 0 1.051.119 2.074.349 3.056-11.144-.559-21.025-5.897-27.639-14.012a13.351 13.351 0 0 0-1.816 6.742c0 4.651 2.369 8.757 5.965 11.161a13.314 13.314 0 0 1-6.073-1.679l-.001.17c0 6.497 4.624 11.916 10.757 13.147a13.362 13.362 0 0 1-3.532.471c-.866 0-1.705-.083-2.523-.239 1.706 5.326 6.657 9.203 12.526 9.312a26.904 26.904 0 0 1-16.655 5.74c-1.08 0-2.15-.063-3.197-.188a37.929 37.929 0 0 0 20.553 6.025c24.664 0 38.152-20.432 38.152-38.153 0-.581-.013-1.16-.039-1.734a27.192 27.192 0 0 0 6.692-6.94z"></path></svg> </span> <br> <span>资深软件开发工程师，业余马拉松选手。</span> </div>
Java的包除了提供底层锁、并发集合外，还提供了一组原子操作的封装类，它们位于包。
我们以为例，它提供的主要操作有：
- 增加值并返回新值：
- 加1后返回新值：
- 获取当前值：
- 用CAS方式设置：
Atomic类是通过无锁（lock-free）的方式实现的线程安全（thread-safe）访问。它的主要原理是利用了CAS：Compare and Set。
如果我们自己通过CAS编写，它大概长这样：
CAS是指，在这个操作中，如果的当前值是，那么就更新为，返回。如果的当前值不是，就什么也不干，返回。通过CAS操作并配合循环，即使其他线程修改了的值，最终的结果也是正确的。
我们利用可以编写一个多线程安全的全局唯一ID生成器：
通常情况下，我们并不需要直接用循环调用实现复杂的并发操作，而是用这样的封装好的方法，因此，使用起来非常简单。
在高度竞争的情况下，还可以使用Java 8提供的和。
使用提供的原子操作可以简化多线程编程：
- 原子操作实现了无锁的线程安全；
- 适用于计数器，累加器等。
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