ConcurrentModificationException錯誤

一.問題:如果不加break會報ConcurrentModificationException異常

1.第一種方法加break
  List<ShopcartBO> shopcartList = JsonUtils.jsonToList(shopcartJson, ShopcartBO.class);
            // 判斷購物車中是否存在已有商品，如果有的話則刪除
            for (ShopcartBO sc: shopcartList) {
                String tmpSpecId = sc.getSpecId();
                if (tmpSpecId.equals(itemSpecId)) {
                    shopcartList.remove(sc);
                    break;
                }
            }

2.第二種方法：iterator 
 List<ShopcartBO> shopcartList = JsonUtils.jsonToList(shopcartJson,ShopcartBO.class);
        Iterator<ShopcartBO> iterator = shopcartList.iterator();
        while (iterator.hasNext()){
           String ss = iterator.next().getSpecId();
           if(ss.equals(itemSpecId)){
               iterator.remove();
           }