错误就在如果依赖对象还未被加载条件成立后，ref = createBeanByConfig(bean); 这句代码的问题是什么了，很明显我一不小心又把当前要创建的bean对象的配置信息传入createBeanByConfig方法中了，所以就会无限递归下去，最后发生StackOverflowError错误。

至于为什么我的测试代码能通过也是比较凑巧，我的测试bean是一个A类，一个B类，其中B类依赖A类对象，所以我们要把A类对象注入到B类中，但是就是这么巧，读取配置文件的时候先读到了A类，所以在要创建B类对象时，A类对象已经创建好了，ref == null就为false，也就是说没执行到那句错误代码，所以就没发现……

要是我改为A类依赖B类，那就可以发现问题了，因为要创建A类对象时，B类对象还没创建。

这些操作基本类型数据的原子类的使用是非常简单的，你对基本类型数据的操作，在这些相应的类中可以找到一些相应的方法。比如说的i++和++i，就分别对应着getAndIncrement()和incrementAndGet()方法，还有像加法如i = i + 3就对应着addAndGet(int delta)方法。

这3个类的操作是类似的，只要你看得懂英文一眼就知道它们的方法是做什么的。需要再次强调的是，这些方法都是原子操作，类似于同步方法，但是没有使用synchronized关键字，也没有锁什么的，而是用CAS+volatile关键字实现原子操作的，关于这点，在后面我会介绍一下原子类的实现。如果还不知道原子操作是什么，我建议你先去看详解JUC之原子类概述，而且里面有原子类解决多线程安全问题的例子，在这里就不重复展示了。

再回到我们的AtomicInteger源码，为了方便看我再把int addAndGet(int delta)方法贴上来，可以看见这个方法中的唯一一句代码是unsafe调用了方法getAndAddInt并将方法的返回值（先get再add说明返回的是value，就像i++先使用i值再进行i+1）加上delta得到的值作为最终返回结果，看方法名我们就很容易理解它到底干了什么。

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