在Android的ThreadLocal代码中看到了两行代码：
private static AtomicInteger hashCounter = new AtomicInteger(0);
private final int hash = hashCounter.getAndAdd(0x61c88647 * 2);对于这两行代码个人理解不好，问题在于对于同一个ThreadLocal实例，既然hash用final修饰了，那么它的值应该是固定的，而且第一个实例的hash变量应该为0才对。这个理解对吗？
但是个人调试了下，发现这个对于同一个ThreadLocal实例，这个值有可能发生变化（我是在使用set函数然后在断点打进去看的）。另外，这个值应该是用于计算散列码，这么写不会有问题么？
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Since the variable hash is final, once it is assigned a value, its value will not change thereafter.
Since the value of hash depends on hashCounter, the value of hash may be different, depending on whether hashCounter has called a method similar to increment, add or set before assigning a value to hash.