How to do image rendering using bufferedimage in a jframe?

I am trying to render a complicated set of objects, and instead of trying to render each object individually, I thought it would be faster to render them as a BufferedImage. The only way I could figure out how to do that was to turn the BufferedImage into an ImageIcon, and set that to a JLabel, and add the JLabel to the JFrame. To update the image, I remove the JLabel, set it with the new BufferedImage, and re-add it to the JFrame. This makes the screen flash rapidly as you can see an empty frame in between each rendering. If I don’t remove the label, the program runs extremely slowly. How do I fix this? Should I even be using JLabels or is there a better way?

    public static void createWindow() {
        frame = new JFrame("PlanetSim");
        
        frame.setPreferredSize(new Dimension(WINDOW_X, WINDOW_Y));
        frame.setMaximumSize(new Dimension(WINDOW_X, WINDOW_Y));
        frame.setMinimumSize(new Dimension(WINDOW_X, WINDOW_Y));

        foregroundLabel = new JLabel(new ImageIcon(foreground));
        
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setResizable(false);
        frame.add(foregroundLabel);
        frame.pack();
        
        frame.setVisible(true);
    }

    public static void setForeground() {
        frame.getContentPane().remove(foregroundLabel);
        foregroundLabel = new JLabel(new ImageIcon(foreground));
        frame.getContentPane().add(foregroundLabel);
        frame.pack();
    }

I doubt the problem has to do with the loop itself, but I’m including it anyway just in case.

    public void run() {
        long lastTime = System.nanoTime(), now; //keeps track of time on computer in nanoseconds
        double amountOfTicks = 60.0; //number of ticks per rendering
        double delta = 0; //time step 
        long timer = System.currentTimeMillis(); //timer to display FPS every 1000 ms
        int frames = 0;

        while (running) {
            now = System.nanoTime();
            delta += (now - lastTime) * amountOfTicks / 1000000000;
            lastTime = now;
            while(delta >= 1) {
                tick();
                delta--;
            }
            if (running)
                render();
            frames++;

            if (System.currentTimeMillis() - timer > 1000) {
                timer += 1000;
                System.out.println("FPS: " + frames);
                frames = 0;
            }
        }   
    }

    public void render() {
        populateWindow();
        Window.setForeground();
    }

Answer

    frame.getContentPane().remove(foregroundLabel);
    foregroundLabel = new JLabel(new ImageIcon(foreground));
    frame.getContentPane().add(foregroundLabel);
    frame.pack();

I would suggest there is no need to remove/add the label or pack the frame since I would assume the Icon will be the same size every time.

All you need to do is replace the Icon of the label.

    //frame.getContentPane().remove(foregroundLabel);
    foregroundLabel.setIcon( new ImageIcon(foreground) );
    //frame.getContentPane().add(foregroundLabel);
    //frame.pack();

I am trying to render a complicated set of objects, and instead of trying to render each object individually, I thought it would be faster to render them as a BufferedImage

Otherwise just do the rendering in your paintComponent() method. Swing is double buffered by default so it essentially removes the need to create the BufferedImage.

See: get width and height of JPanel outside of the class for an example of custom painting. Just update the ball count from 5 to 100 to make it more complex.