Headsup note: if you put one element in a list ( or array) twice, when the list gets serialized, you'll get two copies of that element, instead of one copy being in the new list twice. 特别注意:如果你放一个元素在一个列表(或者数组)两次,当列表被序列化的时候,你将得到两个这个元素的拷贝,而不是一个拷贝两次在新的列表。