Object Oriented, GUIs, and ArrayLists

package objects;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;

public class Main {

    private JFrame frame = new JFrame();
    private JButton btnAddUser = new JButton();
    private JButton btnDisplay = new JButton();

    //User Variables:
    private ArrayList<User> userArray = new ArrayList<User>();
    private String name;
    private String strId;
    private int id;

    public Main() {

        //Frame Attributes:
        frame.setLayout(null);
        frame.setTitle("User Data");
        frame.setSize(400, 600);
        frame.setVisible(true);
        frame.setResizable(false);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //btnAddUser Attributes:
        btnAddUser.setText("Add User");
        btnAddUser.setSize(200, 50);
        btnAddUser.setLocation(90, 100);

        //btnAddUser Click Event:
        btnAddUser.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent arg0) {
                name = JOptionPane.showInputDialog("Enter Name: ");
                strId = JOptionPane.showInputDialog("Enter ID: ");
                id = Integer.parseInt(strId);

                //Add User To Array:
                User newUser = new User(name, id);
                userArray.add(newUser);
            }
        });

        //btnDisplay Attributes:
        btnDisplay.setText("Display");
        btnDisplay.setSize(200, 50);
        btnDisplay.setLocation(90, 200);

        //btnDisplay Click Event:
        btnDisplay.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent arg0) {
                for(int i = 0; i < userArray.size(); i++){
                    JOptionPane.showMessageDialog(null, "Name: " + userArray.get(i).getName());
                    JOptionPane.showMessageDialog(null, "ID: " + userArray.get(i).getID());
                }
            }
        });

        //Add Frame Objects:
        frame.add(btnAddUser);
        frame.add(btnDisplay);
    }

    public static void main(String[] args){
        new Main();
    }

}


package objects;

public class User {

    private String name;
    private int id;

    public User(String newName, int newID) {
        name = newName;
        id = newID;
    }

    public String getName(){
        return name;
    }

    public int getID(){
        return id;
    }

}