10_2, list foreach遍歷刪除 list.remove(obj)報錯ConcurrentModificationException原因

**foreach刪除元素報錯java.util.ConcurrentModificationException**

 private static void removeList(){
        List<Integer> list = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            list.add(i);
        }

        for (Integer string : list) {  //刪除報錯
            list.remove(string);
        }
    }

list修改會記錄修改的次數, 在ArrayList和Itr內部內中都有記錄
ArrayList modCount
Itr expectedModCount Itr是 ArrayList的內部類,實現了迭代器

每次修改modCout都會+1，調用迭代器的remove(),
第一步: ArrayList.this.remove(lastRet);會先去刪除, modCount+1
第二步: 後面設置expectedModCount = modCount;

foreach遍歷實際就是 調用Itr迭代器遍歷,
Itr.next() 會調用checkForComodification()方法, 如果用list的remove(obj)方法, modCount被修改了
, 但是Itr迭代器中的expectedModCount沒有變。 在Itr.next()中校驗失敗

 private class Itr implements Iterator<E> {
 public void remove() {
            if (lastRet < 0)
                throw new IllegalStateException();
            checkForComodification();

            try {
                ArrayList.this.remove(lastRet);
                cursor = lastRet;
                lastRet = -1;
                expectedModCount = modCount;
            } catch (IndexOutOfBoundsException ex) {
                throw new ConcurrentModificationException();
            }
        }
 public E next() {
            checkForComodification();
           	...
        }
final void checkForComodification() {
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
        }

foreach循環刪除報錯,可查看: https://blog.csdn.net/m0_37372711/article/details/54613741