Why isn't my JFrame displaying anything from my Jpanel? - jframe

Question

I'm working on creating a 3 man's morris board, but nothing is being displayed on the frame. It's empty despite having added my JPanel. Everything is fine if I used board = new JPanel(new GridLayout()); and do the following, but I wouldn't be able to draw the lines that would draw the board. I've looked over it a few times but can't seem to find a problem.
public class Project5 extends JFrame {
public final static int FRAME_WIDTH = 600;
public final static int FRAME_HEIGHT = 600;
private JButton jb[] = new JButton[9];
private Board board = new Board();
Project5(){
for(int i = 0; i<9; i++){
jb[i] = new JButton();
board.add(jb[i]);
}
add(board);
}
public static void main(String[] args) {
JFrame frame = new Project5();
frame.setTitle("Three Man's Morris");
frame.setSize(Project5.FRAME_WIDTH,Project5.FRAME_HEIGHT);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
}
class Board extends JPanel{
public Board(){
super();
setLayout(new GridLayout(3,0,Project5.FRAME_WIDTH,Project5.FRAME_HEIGHT));
}
#Override
public void paintComponents(Graphics g){
super.paintComponents(g);
g.drawLine(0, Project5.FRAME_WIDTH, 0, Project5.FRAME_HEIGHT);
g.drawLine(0, 0, 0, Project5.FRAME_HEIGHT);
g.drawLine(0,Project5.FRAME_WIDTH,0,0);
g.drawLine(0, Project5.FRAME_HEIGHT, Project5.FRAME_WIDTH, Project5.FRAME_HEIGHT);
g.drawLine(Project5.FRAME_WIDTH, 0, 0, Project5.FRAME_HEIGHT);
g.drawLine(Project5.FRAME_WIDTH,0,Project5.FRAME_WIDTH,Project5.FRAME_HEIGHT);
}
}

Answer 1

The problem is in your GridLayout() parameters :
GridLayout(rows,cols,horizontal_gap,vertical_gap)
in your case, both gaps are 600 (FRAME_WIDTH, FRAME_HEIGHT) !
The buttons are displayed, but they are outside the panel, try to lower the gap,
i.e. : setLayout(new GridLayout(3,0,0,0));
You should see the buttons.