Multiples JFrame does not repaint properly

Question

I am creating a simple application for test purposes that displays a couple of JFrames separately, and each one contains an image.

The problem is that it displays the number JFrames expected based on the count of images on the list, however, only the last one presents the image. All the other ones are empty.

I've already made a debug, and check that the Buffered Image list is exactly as expected, all objects are there, and they are copies of each other as it is a test.

Is there anything wrong with the repaint call (already tried in a variety of places) or with the ImgPanel subclass? That's my only guess of what could be wrong.

public class Main() extends JFrame{

   BufferedImage I;

   public void show(ArrayList<BufferedImage> images){
       int i = 0;
       for(BufferedImage b : images){
           this.I = b;

           Container c = getContentPane();
           c.setLayout(null);
           c.add(new ImgPanel());

           JFrame frame = new JFrame();
           frame.validate();
           frame.repaint();

           frame.setTitle("Execution: "+i);
           frame.getContentPane().add(c);
           frame.setSize(800,600);
           frame.setVisible(true);
           i++;
       }
   }

   public class ImgPanel extends JPanel {
       public imgPanel() { 
           setBounds(0, 0, 800,600);  
       }

       @Override
       public void paint(Graphics g) {
           super.paint(g);
           g.drawImage(I, 0, 0, this);
       }
   }

   public static void main(String[] args){
       //"d" is an Object Already declared
       ArrayList<BufferedImage> images = d.getImages();
       Main m = new Main();
       m.show(images);
   }
}

Answer 1

I'm not sure where the problem was since your code did not compile. This code works (rock solid) reliably. In this GUI, I would tend to replace ImgPanel with a JLabel, YMMV.

import java.awt.*;
import java.awt.image.*;
import javax.swing.*;
import java.util.ArrayList;
import javax.imageio.ImageIO;
import java.net.URL;

public class Main {

   public void show(ArrayList<BufferedImage> images){
       int i = 0;
       for(BufferedImage b : images){

           JFrame frame = new JFrame("Execution: "+i);
           frame.add(new ImgPanel(b));
           frame.pack();
           frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
           frame.setLocationByPlatform(true);
           frame.setVisible(true);
           i++;
       }
   }

   public class ImgPanel extends JPanel {

       BufferedImage i;

       public ImgPanel(BufferedImage image) {
           i = image;
       }

       @Override
       public Dimension getPreferredSize() {
           return new Dimension(i.getWidth(), i.getHeight());
       }

       @Override
       public void paintComponent(Graphics g) {
           super.paintComponent(g);
           g.drawImage(i, 0, 0, this);
       }
   }

   public static void main(String[] args) throws Exception {
       final ArrayList<BufferedImage> images = new ArrayList<BufferedImage>();
       String[] urlStrings = {
           "https://i.stack.imgur.com/XZ4V5.jpg",
           "https://i.stack.imgur.com/7bI1Y.jpg",
           "https://i.stack.imgur.com/OVOg3.jpg",
           "https://i.stack.imgur.com/lxthA.jpg"
       };
       for (String s : urlStrings) {
           URL url = new URL(s);
           BufferedImage bi = ImageIO.read(url);
           images.add(bi);
       }
       Runnable r = new Runnable() {
           public void run() {
               Main m = new Main();
               m.show(images);
           }
       };
       SwingUtilities.invokeLater(r);
   }
}

Answer 2

Based on your, incomplete, code example and the description of your problem, I would suggest that the problem has to do with your attempt to add a single instance of a component to multiple containers, for example...

Container c = getContentPane();
c.setLayout(null);
c.add(new ImgPanel());
//...
frame.getContentPane().add(c);

A component can only reside in a single container, when a component is added to a new container, it is first removed from it's current container (if it has a parent).

You can test this by setting the ImgPanel background color to something else, like setBackgroundColor(Color.RED), the only frame that will appear red should be the last one...

• You should avoid null layouts, in this specific case, you could does not take into account the borders frames, meaning the content area will expand beyond the viewable area of the frame. Frame borders are also different sizes on different look and feels/platforms
• It's generally encouraged to use paintComponent over paint as it reduces the risks of weirdness and potentially breaking the paint chain
• I'll overlook the fact that it would be simpler to use a JLabel to accomplish this

Answer 3

When using a JPanel, use paintComponent(Graphics)

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);
}