Question

Right now i change the background color of a button by using

button.setBackground(Color.WHITE);

That being an example.

But when i have a massive grid out of jbuttons (1000+), just running a for loop to change every buttons background is very, very slow. You can see the grid slowly turning white, box by box. I really don’t want this

Is there a better way of changing every JButton on the grid to the same color at the same time?

This is how i am making the grid, the numbers used are only for example…

grid = new JPanel(new GridLayout(64, 64, 0, 0));

That’s 4096 buttons, takes about 30+ seconds to change every button to the same color.

Edit 1: I need the buttons to be clickable, like when i click a button it turns blue for example. when all of the buttons are clicked, change the color of every button to white. Right now i have that working fine, but it is just slow to change the color of every button.

Edit 2: this is how i am changing the buttons:

    new javax.swing.Timer(300, new ActionListener() {
        int counter = 0;
        public void actionPerformed(ActionEvent e) {
            if (counter >= counterMax) {
                ((Timer) e.getSource()).stop();
            }
            Color bckgrndColor = (counter % 2 == 0) ? flashColor : Color.white;
            for (JButton button : gridButton) {
                button.setBackground(bckgrndColor);
            }
            counter++;
        }
    }).start();

Answer 1

The fact that you see the boxes being repainted individually indicates that either double buffering is turned off, or that the paint code in the button UI makes use of paintImmediately().

I tested your setup with 64×64 JButtons, an made sure that all UI operations were executed in the EDT (Event Dispatch Thread). I can confirm the effect you saw, changing the background of all buttons took about 1200 ms, with every box repainted immediately.
You can bypass the immediate repaints by setting the grid to non-visible before, and to visible after you changed the backgrounds:

grid.setVisible(false);
for (Component comp : grid.getComponents()) {
   comp.setBackground(color);
}
grid.setVisible(true);

This caused the grid to do only one repaint, and reduced the time to ~300ms (factor 4).

This is still too slow for frequent updates, so you’re better off with a custom component which draws the grid, or a flyweight container (what trashgod suggested in the comment to your question) if you want allow the grid cells to be arbitrary components.