1     List<String> list = new ArrayList<String>();
2         list.add("1");
3         list.add("2");
4         for (String item : list) {
5             System.out.println("item:" + item);
6             if ("1".equals(item)) {
7                 list.remove(item);
8             }
9         }

 1     private class Itr implements Iterator<E> {
 2         int cursor;       // index of next element to return
 3         int lastRet = -1; // index of last element returned; -1 if no such
 4         int expectedModCount = modCount;
 5
 6         public boolean hasNext() {
 7             return cursor != size;
 8         }
 9
10         @SuppressWarnings("unchecked")
11         public E next() {
12             checkForComodification();
13             int i = cursor;
14             if (i >= size)
15                 throw new NoSuchElementException();
16             Object[] elementData = ArrayList.this.elementData;
17             if (i >= elementData.length)
18                 throw new ConcurrentModificationException();
19             cursor = i + 1;
20             return (E) elementData[lastRet = i];
21         }
22
23         public void remove() {
24             if (lastRet < 0)
25                 throw new IllegalStateException();
26             checkForComodification();
27
28             try {
29                 ArrayList.this.remove(lastRet);
30                 cursor = lastRet;
31                 lastRet = -1;
32                 expectedModCount = modCount;
33             } catch (IndexOutOfBoundsException ex) {
34                 throw new ConcurrentModificationException();
35             }
36         }
37
38         final void checkForComodification() {
39             if (modCount != expectedModCount)
40                 throw new ConcurrentModificationException();
41         }
42     }

 1 public boolean remove(Object o) {
 2         if (o == null) {
 3             for (int index = 0; index < size; index++)
 4                 if (elementData[index] == null) {
 5                     fastRemove(index);
 6                     return true;
 7                 }
 8         } else {
 9             for (int index = 0; index < size; index++)
10                 if (o.equals(elementData[index])) {
11                     fastRemove(index);
12                     return true;
13                 }
14         }
15         return false;
16     }

1    */
2     private void fastRemove(int index) {
3         modCount++;
4         int numMoved = size - index - 1;
5         if (numMoved > 0)
6             System.arraycopy(elementData, index+1, elementData, index,
7                              numMoved);
8         elementData[--size] = null; // clear to let GC do its work
9     }