问题描述
我在编写旅行推销员程序时遇到了这个问题.对于内部循环，我尝试了
I've run into this while writing a Traveling Salesman program. For an inner loop, I tried a
for(Point x:ArrayList<Point>) {
// modify the iterator
}
但是当向该列表添加另一个点时会引发 ConcurrentModicationException.
but when adding another point to that list resulted in a ConcurrentModicationException being thrown.
但是，当我将循环更改为
However, when I changed the loop to
for(int x=0; x<ArrayList<Point>.size(); x++) {
// modify the array
}
循环运行良好，没有抛出异常.
the loop ran fine without throwing an exception.
都是for循环，为什么一个会抛出异常而另一个不会呢?
Both a for loops, so why does one throw an exception while the other does not?
推荐答案
正如其他人解释的那样，迭代器检测到对底层集合的修改，这是一件好事，因为它可能会导致意外行为.
As others explained, the iterator detects modifications to the underlying collection, and that is a good thing since it is likely to cause unexpected behaviour.
想象一下这个修改集合的无迭代器代码:
Imagine this iterator-free code which modifies the collection:
for (int x = 0; list.size(); x++)
{
obj = list.get(x);
if (obj.isExpired())
{
list.remove(obj);
// Oops! list.get(x) now points to some other object so if I
// increase x again before checking that object I will have
// skipped one item in the list
}
}
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