遍歷整個 List並且移除符合條件的物件要用 Iterator.remove()或 List.remove(index)

要遍歷整個 Collection並且移除符合條件的物件, 用 for (Object obj : list)不可行(throw ConcurrentModificationException)
要用 Iterator迭代並且用 Iterator.remove()移除(原始 list會被修改).

下面的程式碼不可行(throw ConcurrentModificationException)
List<Integer> list = new ArrayList<Integer>();
for (int i = 0; i < 100; i++) {
list.add(Integer.valueOf(i));
}

String point1 = "point1: ";

String point2 = "point2: ";

for (Integer integer : list) {
log.debug(point1 + list.size());
if (integer % 7 == 0) {
list.remove();
}
log.debug(point2 + list.size());
}

必須用傳統的 for(int i=0....

Integer integer = null;

  for (int i = 0; i < list.size(); i++) { log.debug(point1 + list.size()); integer = list.get(i); if (integer % 7 == 0) { list.remove(i); } log.debug(point2 + list.size()); }
或 Iterator.remove()

Integer integer = null;

for (Iterator<Integer> itr = list.iterator(); itr.hasNext();) {

log.debug(point1 + list.size());

integer = itr.next();

if (integer % 7 == 0) {

itr.remove();

}

log.debug(point2 + list.size());

}