java - ConcurrentModificationException，需要澄清

Question

这个问题已经有答案了:

Iterating through a Collection, avoiding ConcurrentModificationException when removing objects in a loop (31 个回答)

已关闭 7 年前。

以下模型代码最终出现在 ConcurrentModificationException 中，这种情况发生(据我所知)，因为我正在迭代一个我正在修改的集合。

Set<String> data = new HashSet<String>();
data.add("a=1");
data.add("b=2");
data.add("c=3");
data.add("d=4");

for (String s : data) {
    data.remove(s);
}

但是到底为什么呢？请帮忙澄清一下

Answer 1

您违反了迭代器的契约。来自 ConcurrentModificationException javadoc ,

If a single thread issues a sequence of method invocations that violates the contract of an object, the object may throw this exception. For example, if a thread modifies a collection directly while it is iterating over the collection with a fail-fast iterator, the iterator will throw this exception.