Displaying JLabel matrix
<p>Can somebody tell me why after calling method getContentPane().add(grid[i][j]) I am not able to display the matrix of JLabels. There's only one "e" label displayed.</p>

<p>public class SudokuFrame extends JFrame implements ActionListener {</p>

<pre><code>JButton generateButton;
JLabel[][] grid;

public SudokuFrame(){
    setSize(300, 300);
    setTitle("Sudoku");
    setLayout(null);
    generateButton = new JButton("Generate");
    generateButton.setBounds(90, 220, 100, 30);
    add(generateButton);
    generateButton.addActionListener(this);

    grid = new JLabel[9][9];
    for (int i = 0; i &lt; 9; i++) {
        for (int j = 0; j &lt; 9; j++) {
            grid[i][j] = new JLabel("e");
            grid[i][j].setBounds(100, 100, 30, 30);
            getContentPane().add(grid[i][j]);
        }
    }
}

public static void main(String[] args){
    SudokuFrame frame = new SudokuFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
}
</code></pre>