public class ArrayList<e> extends AbstractList<e>

        implements Cloneable, Serializable, RandomAccess {

         @Override public boolean remove(Object object) {

        Object[] a = array;

        int s = size;

        if (object != null) {

            for (int i = 0; i < s; i++) {

                if (object.equals(a[i])) {

                    System.arraycopy(a, i + 1, a, i, --s - i);

                    a[s] = null;  // Prevent memory leak

                    size = s;

                    modCount++;  // 只要删除成功都是累加

                    return true;

                }

            }

        } else {

            for (int i = 0; i < s; i++) {

                if (a[i] == null) {

                    System.arraycopy(a, i + 1, a, i, --s - i);

                    a[s] = null;  // Prevent memory leak

                    size = s;

                    modCount++;  // 只要删除成功都是累加

                    return true;

                }

            }

        }

        return false;

    }   

    @Override public Iterator<e> iterator() {

        return new ArrayListIterator();

    }   

    private class ArrayListIterator implements Iterator<e> {

          ......

          // 全局修改总数保存到当前类中

        /** The expected modCount value */

        private int expectedModCount = modCount;

        @SuppressWarnings("unchecked") public E next() {

            ArrayList<e> ourList = ArrayList.this;

            int rem = remaining;

               // 如果创建时的值不相同，抛出异常,

            if (ourList.modCount != expectedModCount) {

                throw new ConcurrentModificationException();

            }

            if (rem == 0) {

                throw new NoSuchElementException();

            }

            remaining = rem - 1;

            return (E) ourList.array[removalIndex = ourList.size - rem];

        }   

          ......

     }

}