Do not modify the list, but still get a ConcurrentModificationException

Question

Before your eyes look back at another ConcurrentModificationException question, this is not your typical ConcurrentModificationException question.

I understand ConcurrentModificationExceptions, but I do not understand why I get it in the following code. The "for" below shows that the iterator continues to live outside the for loop. (Using the debugger in eclipse, I see that the iterator preserves the jList modCount value when the loop restarts.)

public class ForEachTest {
  public static void main(String[] args) {
    List<Integer> zList = new LinkedList<Integer>();
    List<Integer> jList = new LinkedList<Integer>();
    jList.add(1);

    while (true) {
      for (Integer j : jList) {
        zList.add(17);
        System.out.println(j);
      }
      jList = zList;
    }
  }
}

At first I thought it might be a syntactic sugar problem, but I rewrote it with an explicit iterator and came across the same behavior.

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Answer 1

:

while (true) {
  for (Integer j : jList) {
    zList.add(17);
    System.out.println(j);
  }
  jList = zList;
}

jList zList (- jList = zList;)... , zList , " , . .