合併一個List中相同元素，並彙總指定屬性

 

public static void mergeList(List<Bean> list) {
    HashMap<String, Bean> map = new HashMap<String, Bean>();
    for (Bean bean : list) {
        if (map.containsKey(bean.getType())) {
            bean.setQuantity(map.get(bean.getType()).getQuantity() + bean.getQuantity());
        }
        map.put(bean.getType(), bean);
    }
    list.clear();
    list.addAll(map.values());
}