故障安全迭代器 - 在迭代期间移除

Question

If fail safe iterator creates a clone of underlying data structure, why 'D' is never printed in program below?

Map<String, String> acMap = new ConcurrentHashMap<String, String>();
acMap.put("A", "Aye");
acMap.put("B", "Bee");
acMap.put("C", "See");
acMap.put("D", "Di");

Iterator<String> itr = acMap.keySet().iterator();
while(itr.hasNext())
{
    acMap.remove("D");
    System.out.println(itr.next());
}

Answer 1

根据文档，地图上的任何操作都将反映在键集上，反之亦然。并且 KeySet#iterator() 也不会克隆底层 ds.

ConcurrentHashMap#keySet():

Returns a Set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. The set supports element removal, which removes the corresponding mapping from this map, via the Iterator.remove, Set.remove, removeAll, retainAll, and clear operations.

Read more documentation

See openjdk Implementation

Answer 2

正如 Javadoc for keySet() 中所说：

The iterator ... may (but is not guaranteed to) reflect any modifications subsequent to construction.

您的迭代器是反映构造后的修改。