How to cleanly interact with nested class in java?

Question

How can one store & access attributes in the following way in Java?

InnerTest it = new InnerTest();
it.id = "123";
it.user.userID = "456";

The following code does not do what is desired, but it offers a backdrop for the question:

public class InnerTest {
    public String id;
    static class user {
        static String userName;
        static String userID;
    }
}

In case my approach is way off, the exercise is to store a JSON architecture in a class, but access it simply as given above. I am creating a class for Tweets, and one inner group of attributes is under "user":

[...]
 "in_reply_to_user_id" : null,
  "in_reply_to_user_id_str" : null,
  "in_reply_to_screen_name" : null,
  "user" : {
    "id" : 19792676,
    "id_str" : "19792676",
    "name" : "(((Payne¯\\_(ツ)_/¯)))",
[...]

I am looking for a way to elegantly represent in my class' use those inner variables, as in:

foo.user.id_str ...

Is a type of nested/anonymous class correct? It doesn't look like it is-even with static modifiers...

That is a nested class, not an inner class. Also, why are the member variables static at all? Your JSON seems to indicate that a `InnerTest` should have a field of type `user`. — Sotirios Delimanolis, Jun 19 '16 at 15:06
@SotiriosDelimanolis, like I said, the class I was playing with in scratch was just a backdrop for the question. Thanks for the edits... — Yumi Koizumi, Jun 20 '16 at 01:12
If you are serializing with GSON, I recommend you [@SerializedName](https://google.github.io/gson/apidocs/com/google/gson/annotations/SerializedName.html) annotation. You won't have to use the underscored names as your variable names. — Jezor, Jun 20 '16 at 02:50

Sergey Kalinichenko · Accepted Answer · 2016-06-20T01:31:17.320

1

Nested class is a good choice in this situation. However, you misunderstood the purpose of static in a static class - this is a syntax for creating classes that can be created independently of the instance of their outer class. It is not a class that must have only static fields and methods.

Therefore, your declaration should be fixed to make userName and userId fields non-static:

public class InnerTest {
    public String id;
    public UserType user = new UserType();
    static class UserType {
        String userName;
        String userID;
    }
}

edited Jun 20 '16 at 01:31

answered Jun 19 '16 at 15:09

Sergey Kalinichenko

714,442
84
1,110
1,523

thanks for writing. I appreciate the correction, but I may be missing how to access these inner member from the outer instance, a la: ` InnerTest it = new InnerTest(); it.id = "123"; it.user.userName = "456";` ...where all variables, however nested, can be accessed via a minimalistic way, such as: it.user.userID, etc. Is that simply not possible? – Yumi Koizumi Jun 20 '16 at 01:25
@YumiKoizumi You need to create a field called `user` for the nested type. Please see the edit. – Sergey Kalinichenko Jun 20 '16 at 01:33
@dasblinkinlight ...Perfect! Really great! I was beginning to think Java couldn't do it! Thank you! :) – Yumi Koizumi Jun 20 '16 at 01:45

score 1 · Answer 2 · edited May 23 '17 at 10:33

1

Your nested class definition have static fields, which are bound to a class rather than to objects. If we change them to public, the definition will be correct, although you still didn't add a member variable of this class inside the InnerTest class. Take a look at this answer, it clarifies the difference between class definition and object instance.

public class InnerTest {
    public String id;
    public User user;

    static class User {
        public String userName;
        public String userID;
    }
}

Now you can create a new InnerTest object and access user data the way you intended.

edited May 23 '17 at 10:33

Community

1
1

answered Jun 19 '16 at 15:12

Jezor

3,253
2
19
43

I am sorry to not have made clearer the way I intended. I intended to access inner variables from the same instance, avoiding making many instances to represent a single class (at the top). This is why `it.user.userID = "456";` is desired. Representing a JSON tweet, which has a ton of nested structures, would get messy very fast with instances of all inner classes. Hopefully java has a way to do this simply... – Yumi Koizumi Jun 20 '16 at 01:30

How to cleanly interact with nested class in java?

2 Answers2