public Object opt(int index) {
        if (index < 0 || index >= this.length()) {
            return null;
        }
        Object value = list.get(index);
        if (value == JSONObject.NULL) {
            return null;
        }
        return value;
    }
@author Robert HG (254963746@qq.com) on 12/28/15.
lts-core/src/main/java/com/github/ltsopensource/json/JSONArray.java