Cannot resolve method 'keys' in 'JSONObject'

//""自定义

String str = "";

JSONObject object = JSONObject.fromObject(str);
Map<String, Object> conditionMap = new HashMap<String, Object>();
Iterator<String> iterator = object.keys();
while (iterator.hasNext()){
    String key = (String) iterator.next();
    String val = object.getString(key);
    System.out.println("[key="+key+"--> val="+val+"]");
    conditionMap.put(key, val);
}

用

Iterator<String> iterator = object.keySet().iterator(); 

替换 

Iterator<String> iterator = object.keys();