Why aren't my images being added to my JButtons?

Question

I have a program that consists of four JButtons in a JFrame. I want to add images to the JButtons. The problem is that I can't seem to add them, despite trying multiple methods. When compiled, the output is input == null. The images are stored in the same folder as my .java files, so I can't figure out why they aren't showing up.

Main class:

import java.awt.GridLayout;
import java.awt.Image;

import javax.imageio.ImageIO;
import javax.swing.BoxLayout;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class AutoProgram extends JFrame {

    private static String[] files    = {"workA","programmingA","leisureA","writingA"};
    private static JButton[] bIcons  = new JButton[4];
    private static Image[] bImg      = new Image[4];

    public AutoProgram() {
        super("Automation Project V.1");

        JPanel autoIcons = new JPanel();
        autoIcons.setLayout(new GridLayout(2,2));

        // Initialize the four buttons (w/ images)
        for(int i = 0; i < files.length; i++) {
            bIcons[i] = new JButton();
            try {
                bImg[i] = ImageIO.read(getClass().getResource(files[i].toLowerCase() + ".png"));
                bIcons[i].setIcon(new ImageIcon(bImg[i]));
            } catch (Exception ex) {
                System.out.println(ex);
            }
            autoIcons.add(bIcons[i]);
        }

          JPanel mainPanel = new JPanel();
          mainPanel.setLayout(new BoxLayout(mainPanel, BoxLayout.PAGE_AXIS));;
          mainPanel.add(autoIcons);
          add(mainPanel);

          pack();

}}

Window class:

public class Window {

    public static void main(String[] args) {

        AutoProgram frame = new AutoProgram();

        frame.setSize(315,315);
        frame.setLocationRelativeTo(null);
        frame.setFocusable(true);
        frame.setResizable(true);
        frame.setVisible(true);
    }
}

Any help would be greatly appreciated. Thanks!

Answer 1

Before going into the answer to your question, please read the following recommendations:

1. private static JButton[] bIcons = new JButton[4]; Creating static fields could break your program, so be careful when to use them. Not really needed in this case, please read What does the 'static' keyword do in a class?

2. JFrame is a rigid container which cannot be placed inside others, and you're not changing it's functionallity anywhere in your program, so there's no need to call extends JFrame, it's better to create a JFrame instance then. See: Extends JFrame vs. creating it inside the program for more information about this.

3. You're correctly calling pack() but later in the code you're calling frame.setSize(315,315); which "destroys" the changes made by pack(), use one or the other, not both, I recommend you to leave pack() call.

4. You're not placing your program in the Event Dispatch Thread (EDT), you can fix it by changing your main(...) method as follows:

   public static void main (String args[]) {
       //Java 7 and below
       SwingUtilities.invokeLater(new Runnable() {
           //Your code here
       });
   
       //Java 8 and higher
       SwingUtilities.invokeLater(() -> {
           //Your code here
       });
   }
   

---

Now, let's go to the solution:

Your code works fine, I think that your errors might come from the following posibilities:

• Calling files[i].toLowerCase() (.toLowerCase() method might be breaking your program, Java is case sensitive).
• Your images are not PNG but JPG or JPEG (look at the extension carefully)
• Your images are damaged