Java技术疑问：下述代码结构为何未抛出ConcurrentModificationException？

Great question! Let's break down why ConcurrentModificationException isn't showing up here.

First, let's recap when this exception is triggered: ConcurrentModificationException usually occurs when you structurally modify a collection (like adding, removing, or clearing elements) while iterating over it with its built-in iterator—and you don't use the iterator's own modification methods (such as Iterator.remove()).

Now let's look at your code:

• In the cancelItem method, you're iterating over myMap.entrySet(), which means you're traversing the entries of the myMap HashMap.
• The modification happening inside the loop targets Node's internal itemIDHashMap (when you call cancelItemFromNode(o)). This is a completely separate collection from myMap.

The key point here is: you're not making any structural changes to myMap itself during the iteration. The <Double, Node> entries in myMap stay exactly as they are—you're only modifying the contents inside each Node instance, not adding or removing entries from myMap itself.

For example, if you tried to do something like myMap.remove(nn.getKey()) inside that loop, you would trigger a ConcurrentModificationException because you're altering the structure of the collection you're actively iterating over. But since that's not what's happening here, the iterator never detects any conflicting modifications, so no exception is thrown.

内容的提问来源于stack exchange，提问作者user1769197