ThreadLocal源码，骚气的for循环 ｜ Java Debug 笔记

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一 ThreadLocal set方法分析

   private void set(ThreadLocal key, Object value) {

    // We don't use a fast path as with get() because it is at
    // least as common to use set() to create new entries as
    // it is to replace existing ones, in which case, a fast
    // path would fail more often than not.

    Entry[] tab = table;
    int len = tab.length;
    int i = key.threadLocalHashCode & (len-1);

    for (Entry e = tab[i];
         e != null;
         e = tab[i = nextIndex(i, len)]) {
        ThreadLocal k = e.get();

        if (k == key) {
            e.value = value;
            return;
        }

        if (k == null) {
            replaceStaleEntry(key, value, i);
            return;
        }
    }

    tab[i] = new Entry(key, value);
    int sz = ++size;
    if (!cleanSomeSlots(i, sz) && sz >= threshold)
        rehash();
}

这里面有一个for循环，很骚气，for循环不是应该for（int i=0;i<list.size();i++）吗？ 或者是foreach的写法吗？

for (Entry e = tab[i];
     e != null;
     e = tab[i = nextIndex(i, len)])
     

就是这段骚气的for循环，仔细看了一下，这段代码其实就是for循环的基础变种，意思就是如果e！=null时就会一直执行下去Entry e = tab[i]是初始值，相当与i =0,e = tab[i = nextIndex(i, len)] 是一个变化的值，相当于i++。

二 结语

源码的阅读不是一蹴而就的，而是需要不断的循序渐进，如果太过着急，就一定会适得其反。