Android LruCache（Android 3.1）线程安全

新的Android类线程安全吗？java文档说：

这个类是线程安全的。通过在缓存上同步，以原子方式执行多个缓存操作：

他们的意思是说线程不安全吗？如果类是线程安全的，为什么要同步

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谢谢

不管类是否是线程安全的。如果使用多个操作，可能仍需要同步。这取决于你如何使用它

if (cache.get(key) == null)
{
  //at this point you think there is no such value in the cache
  //but another thread might have just added one between executing
  //those two lines of code
  cache.put(key, value);
}

if (cache.get(key) == null)
{
  //at this point you think there is no such value in the cache
  //but another thread might have just added one between executing
  //those two lines of code
  cache.put(key, value);
}