JCheckBox not appearing

Question

I have checked everwhere for a fix but nothing can work to make my checkbox appear. I added it to the panel and added the panel to the window. The button is appearing so it must be a problem with the checkbox. Here is my code:

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.Point;
import java.awt.Toolkit;
import java.awt.event.KeyEvent;

import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class MainApplication {

    public static Toolkit tk = Toolkit.getDefaultToolkit();

    public static void main(String[] args) {
        MainApplication instance = new MainApplication();
        instance.start();
    }

    private JFrame window;
    private JPanel mainPanel;
    private JPanel contingencyPanel;

    private JButton applyButton = new JButton("Apply Changes");
    private JCheckBox autoRedLightBox = new JCheckBox("Red Light");
    private JCheckBox autoYellowLightBox = new JCheckBox("Yellow Light");
    private JCheckBox autoGreenLightBox = new JCheckBox("Green Light");
    private JCheckBox autoBlueLightBox = new JCheckBox("Blue Light");

    public void start() {
        window = new JFrame("Main Control Window");
        mainPanel = new JPanel();
        contingencyPanel = new JPanel();

        window.setSize(1280, 720);
        window.setResizable(false);
        window.setFocusable(true);
        window.setFocusTraversalKeysEnabled(true);
        int screenWidth = (int)tk.getScreenSize().getWidth();
        int screenHeight = (int)tk.getScreenSize().getHeight();
        window.setLocation((screenWidth/2)-(window.getWidth()/2), (screenHeight/2)-(window.getHeight()/2));
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        mainPanel.setLayout(null);
        contingencyPanel.setLayout(null);

        applyButton.setToolTipText("Changes will be applied to the arduino.");
        applyButton.setSize(new Dimension(120, 30));
        applyButton.setLocation(new Point((1280-120)-10, (720-56)-10));

        autoRedLightBox.setSelected(true);
        autoRedLightBox.setLocation(new Point(30, 30));
        autoRedLightBox.setMnemonic(KeyEvent.VK_R);

        mainPanel.add(applyButton);
        mainPanel.add(autoRedLightBox, BorderLayout.CENTER);

        window.add(mainPanel);
        window.setVisible(true);
    }
}

Desired Outcome:

Answer 1

Read a bit about LayoutManagers in Swing. Every panel needs a layout to hold components, if you don't specify layout for JPanel it uses default one (FlowLayout). The problem was in this line, when you set null for layout

    mainPanel.setLayout(null);

just comment it and you will see buttons on form. Also, for putting your form in center of screen you can call this method

    window.setLocationRelativeTo(null);

Answer 2

That's well suited to a GridLayout.

import java.awt.*;
import javax.swing.*;
import javax.swing.border.EmptyBorder;

public class ButtonsAndChecks {

    private JComponent ui = null;

    ButtonsAndChecks() {
        initUI();
    }

    public void initUI() {
        if (ui!=null) return;

        // adjust last two numbers to need..
        ui = new JPanel(new GridLayout(0,5,20,20));
        ui.setBorder(new EmptyBorder(4,4,4,4));

        // adjust numbers to need..
        for (int i=1; i<26; i++) {
            ui.add(new JButton("Button " + i));
        }
        // adjust numbers to need..
        for (int i=1; i<26; i++) {
            ui.add(new JCheckBox("Check " + i, i%2==0));
        }
    }

    public JComponent getUI() {
        return ui;
    }

    public static void main(String[] args) {
        Runnable r = new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (Exception useDefault) {
                }
                ButtonsAndChecks o = new ButtonsAndChecks();

                JFrame f = new JFrame(o.getClass().getSimpleName());
                f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
                f.setLocationByPlatform(true);

                f.setContentPane(o.getUI());
                f.pack();
                f.setMinimumSize(f.getSize());

                f.setVisible(true);
            }
        };
        SwingUtilities.invokeLater(r);
    }
}