Grid wont show despite using for loop to create the cells

Question

I am making a 8x8 Othello board and for some reason the buttons I created wont show up. This is how my code looks like now and when it runs all that comes up is a frame with all green. Here is the code, the green comes from the background of the ContentPane. I have watched some tutorials and most seem to implement a grid this way. Can t seem to find the error

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


public class Otello extends JFrame implements ActionListener {

    Random random = new Random();
    JFrame frame = new JFrame();
    JPanel title_panel = new JPanel();
    JPanel button_panel = new JPanel();
    JLabel textfield = new JLabel();
    JButton[][] buttons = new JButton[8][8];
    boolean player1_turn; //Om true är det Player1 tur, vid false är det Player2 tur

    Otello(){

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(800,800);
        frame.getContentPane().setBackground(Color.GREEN);
        frame.setLayout(new BorderLayout());
        frame.setVisible(true);

        textfield.setBackground(new Color(25,25,25));
        //field.setForeground(new Color(25,245,0));
        textfield.setFont(new Font("Ink free",Font.BOLD, 75 ));
        textfield.setHorizontalAlignment(JLabel.CENTER);
        textfield.setText("Otello");
        textfield.setOpaque(true);

        title_panel.setLayout(new BorderLayout());
        title_panel.setBounds(0,0,800,65);

        button_panel.setLayout(new GridLayout(8,8));
        button_panel.setBackground(new Color(150,150,150));


        for(int i = 0; i < 8; i++) {
            for (int j = 0; i < 8; j++) {
                buttons[i][j] = new JButton();
                button_panel.add(buttons[i][j]);
                buttons[i][j].setFocusable(false);
                buttons[i][j].addActionListener(this);
                buttons[i][j].setBackground(Color.RED);
                buttons[i][j].setOpaque(true);
            }
        }

        title_panel.add(textfield);
        frame.add(title_panel,BorderLayout.NORTH);
        frame.add(button_panel);