Java – why does one loop throw a concurrentmodificationexception while the other does not?

I encountered this problem when I was writing a travel salesman plan For the inner loop, I tried one

for(Point x:ArrayList<Point>) {
// modify the iterator
}@H_301_3@ 
 
但是当向该列表添加另一个点时会导致ConcurrentModicationException被抛出.
 
 
但是,当我将循环更改为
 
  
 
for(int x=0; x<ArrayList<Point>.size(); x++) {
// modify the array
}@H_301_3@ 
 
循环运行良好,不会抛出异常.
 
 
一个for循环,那么为什么一个抛出异常而另一个没有？

Solution
As others have explained, iterators detect changes to the underlying collection, which is a good thing because it can lead to unexpected behavior
Imagine this set of code modifications without iterators:
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
  }
}@H_301_3@