Affichage Matrice

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

public class Main {
    public static void main(String[] args) {
        int nbRows = 3, nbCols = 4;
        int[][] matrix = { { 1, 2, 3, 4 }, { 5, 6, 7, 8 }, { 9, 10, 11, 12 } };

        JFrame frame = new JFrame();
        GridLayout grid = new GridLayout(nbRows, nbCols);
        frame.setLayout(grid);

        for (int row = 0; row < nbRows; row++) {
            for (int col = 0; col < nbCols; col++) {
                int value = matrix[row][col];
                int red = 20 * value, green = 255 - red, blue = 0;

                JLabel label = new JLabel(String.valueOf(value), JLabel.CENTER);
                label.setOpaque(true);
                label.setBackground(new Color(red, green, blue));
                frame.add(label);
            }
        }

        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}