Map<String,String> map=new HashMap<String,String>();
map.put("1", "222");
List<Map<String,String>> list = new ArrayList<Map<String,String>>();
list.add(map);
map=null;//沒有效果，list中還是有數據
map.clear();//map沒數據了
Map<String, String> map2 = list.get(0);
System.out.println(map2.size());
System.out.println(map2.get("1"));