JRadioButtons in a custom JScrollPane not appearing?

Question

I'm writing an IM client GUI for a project. On the left of the window, I want a scrolling pane that has radio buttons for each active user, so that when a New Chat button is pushed, a chat will be created with the selected user.

I've implemented a sample GUI with 3 given users. I create a JRadioButton for each, set an ActionCommand and an ActionListener, add it to the ButtonGroup and then add it to 'this', which is a class extending JScrollPane. However, when I run the code, I see only an empty frame on the left hand side, with no buttons present. Can anybody explain? Relevant code is below.

package gui;
import javax.swing.*;

public class ActiveList extends JScrollPane implements ActionListener {
    private ButtonGroup group;
    private String selected;

    public ActiveList() {
        //TODO: will eventually need access to Server's list of active usernames
        String[] usernames = {"User1", "User2", "User3"};
        ButtonGroup group = new ButtonGroup();
        this.group = group;

        for (String name: usernames) {
            JRadioButton button = new JRadioButton(name);
            button.setActionCommand(name);
            button.addActionListener(this);
            this.group.add(button);
            this.add(button);
        }
    }

    public String getSelected() {
        return this.selected;
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        this.selected = e.getActionCommand(); 
        System.out.println(e.getActionCommand());
    }

}

The main method that I'm running comes from another class, ChatGUI.java. The ConversationsPane container is another class in my GUI, which is working correctly.

package gui;
import javax.swing.*;

public class ChatGUI extends JFrame {
    private ConversationsPane convos;
    private ActiveList users;

    public ChatGUI() {
        ConversationsPane convos = new ConversationsPane();
        this.convos = convos;
        ActiveList users = new ActiveList();
        this.users = users;

        GroupLayout layout = new GroupLayout(this.getContentPane()); 
        this.getContentPane().setLayout(layout);
        layout.setAutoCreateGaps(true);
        layout.setAutoCreateContainerGaps(true);

        layout.setHorizontalGroup(
            layout.createSequentialGroup()
                .addComponent(users, 100, GroupLayout.DEFAULT_SIZE, GroupLayout.PREFERRED_SIZE)
                .addComponent(convos)
         );

        layout.setVerticalGroup(
            layout.createParallelGroup()
                .addComponent(users)
                .addComponent(convos)
        );
    }

    public static void main(String[] args) {
        ChatGUI ui = new ChatGUI();
        ui.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        ui.setVisible(true);
        ui.setSize(800,400);
        ui.convos.newChat("Chat A");
    }
}

Answer 1

This is not how scroll panes work. You do not "add" components to them. You set A component to the scroll panes view port

Instead of extending JScrollPane, as you are adding no value to it, try doing something more like...

JScrollPane scrollPane = new JScrollPane();
JPanel view = new JPanel(new GridLayout(0, 1));
String[] usernames = {"User1", "User2", "User3"};
ButtonGroup group = new ButtonGroup();
this.group = group;

for (String name: usernames) {
    JRadioButton button = new JRadioButton(name);
    button.setActionCommand(name);
    button.addActionListener(this);
    this.group.add(button);
    view.add(button);
}

scrollPane.setViewportView(view);
// Add scrollpane to WEST position of main view

Instead...

Take a look at How to use scroll panes for more details...

Answer 2

Instead of extending JScrollPane extend JPanel with proper layout. Add you JRadioButtons to the panel and place the panel in a JScrollPane.