java - 澄清 HashMap 中的 @ConcurrentModificationException

Question

我期待在后续代码中出现 ConcurrentModificationException，但它工作正常。

HashMap<Integer, String>table1 = new HashMap<Integer, String>();
    table1.put(1, "Sam");
    table1.put(2, "Jon");
    table1.put(3, "Doe");

    Iterator itr1 = table1.entrySet().iterator();

    table1.put(3, "DONN");
    while(itr1.hasNext())
    {
        System.out.println("---Value--" + itr1.next());
    }

根据 HashMap 的 JavaDoc:

The iterators returned by all of this class's "collection view methods" are fail-fast: if the map is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove method, the iterator will throw a ConcurrentModificationException.

因为我在获取Iterator 之后修改HashMap，所以我应该获取ConcurrentModificationException。为什么不抛出？

Answer 1

在 HashMap 的当前实现中，为现有键添加条目不被视为结构修改，并且永远不会触发ConcurrentModificationException。尝试使用新 key ，例如table1.put(4, "UPS"); 获取 ConcurrentModificationException。