JSONObject remove elements - substring is removed, the father of the string will be removed

Due

Today, look at the code found why people did not write the code to remove an element but there is no element of it?
Later found the code gets a substring removed an element in the front, the results of the parent nor the element of the string.

phenomenon

Original JSON string is like this: { "a": { "a1": "va1", "a2": "va2"}}

    String jsonString = "{\"a\":{\"a1\":\"va1\",\"a2\":\"va2\"}}";
    com.alibaba.fastjson.JSONObject json= com.alibaba.fastjson.JSONObject.parseObject(jsonString);    
    com.alibaba.fastjson.JSONObject aJson = json.getJSONObject("a");
    aJson.remove("a1");
    System.out.println(json.toJSONString());

Do you think the result of the output of the code above is what is it?
The net effect is: { "a": { " a2": "va2"}}

Explanation

fastjson in JSONObject using HashMap or json LinkedHashMap to save the key-value pairs, getObject (String key) is actually invoked map of get (String key) method, the returned object is a map of the reference object.
It means the following questions:

    Map<String, List<String>> map = new HashMap<>();
    List<String> list = new ArrayList<>();
    list.add("1");
    list.add("2");
    list.add("3");
    
    map.put("aa", list);

    List<String> aaList = map.get("aa");
    aaList.remove(0); 

    List<String> aList = map.get("aa");
    aList.forEach(System.out::println);
            

When the modified object acquired when, map objects will be changed, and therefore the fastjson JSONObject the substring modification causes a corresponding change in the parent sequence.