arrayList add方法只是引用对象地址

List<Map<Stirng,Object>> list = new ArrayList();
Map<String, Object> map = new HashMap<>();
map.put("counter_id", "1");
map.put("pay_no", "000");
map.put("pay_name", "现金");
map.put("amount", "30");
list.add(map);//添加map
map.clear()//将map清空
System.out.println(list);

//输出
[{}]

List<Map<String, Object>> list = new ArrayList<>();
        Map<String, Object> map = new HashMap<>();
        map.put("counter_id", "1");
        map.put("pay_no", "000");
        map.put("pay_name", "现金");
        map.put("amount", "30");
Map<String,Object> n = new HashMap<>();
        n.putAll(tableMap);
        list .add(n);
        map.clear();
        System.out.println(list);        
//输出
 [{amount=30, pay_name=现金, pay_no=000, counter_id=1}]