JPanel doesn't react to MouseEvents?

Question

I'm trying to create a "Tic Tac Toe" game. I've chosen to create a variation of JPanel to represent each square. The class beneath represents one of 9 panels that together make up my game board.
Now the problem I'm having is that when I click the panel a 'X' should be displayed inside of the panel, but nothing happens. I'd very much appreciate it if someone steered me in the right direction.

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

public class TicTacToePanel extends JPanel implements MouseListener {
    private boolean isPlayer1Turn = true;
    private boolean isUsed = false;
    private JLabel ticTacLbl = new JLabel();

    public TicTacToePanel() {
        setBorder(BorderFactory.createLineBorder(Color.BLACK));
        addMouseListener(this);
    }

    public void mouseClicked(MouseEvent e) {
        if (!isUsed) {
            if (isPlayer1Turn) {
                ticTacLbl.setForeground(Color.red);
                ticTacLbl.setText("X");
                add(ticTacLbl, 0);
                isUsed = true;
            } else {
                ticTacLbl.setForeground(Color.blue);
                ticTacLbl.setText("O");
                add(ticTacLbl, 0);
                isUsed = true;
            }

        } else {

        }
    }

    public void mousePressed(MouseEvent e) {

    }

    public void mouseReleased(MouseEvent e) {

    }

    public void mouseEntered(MouseEvent e) {

    }

    public void mouseExited(MouseEvent e) {

    }

    public static void main(String[] args) {
        JOptionPane.showMessageDialog(null, new TicTacToePanel());
    }

}

EDIT:
I simply added my label component in the constructor of my TicTacToePanel so that I no longer have to call revalidate() and I'm not adding components during runtime.

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

public class TicTacToePanel extends JPanel implements MouseListener{
    private boolean isPlayer1Turn = true;
    private boolean isUsed = false;
    private JLabel ticTacLbl = new JLabel();

    public TicTacToePanel(){
        add(ticTacLbl, 0);
        setBorder(BorderFactory.createLineBorder(Color.BLACK));
        addMouseListener(this);
    }

    public void mouseClicked(MouseEvent e){

    }

    public void mousePressed(MouseEvent e){
        if (!isUsed) {
            if (isPlayer1Turn) {
                ticTacLbl.setForeground(Color.red);
                ticTacLbl.setText("X");
                isUsed = true;
            } else {
                ticTacLbl.setForeground(Color.blue);
                ticTacLbl.setText("O");
                isUsed = true;
            }

        }
        else{

        }

    }

     public void mouseReleased(MouseEvent e){

    }

    public void mouseEntered(MouseEvent e){

    }

    public void mouseExited(MouseEvent e){

    }   

     public static void main(String[] args){
        JOptionPane.showMessageDialog(null, new TicTacToePanel());
    }
}

The GUI constructor:

     public TicTacToeGUI(int gameMode){
        if(gameMode == 0){
            amountOfPanels = 9;
            TicTacToePanel[] panelArr = new TicTacToePanel[amountOfPanels];
            add(gamePanel, new GridLayout(3, 3));
            setPreferredSize(new Dimension(100, 100));
            for(int i = 0; i < amountOfPanels; i++){
                panelArr[i] = new TicTacToePanel();
                gamePanel.add(panelArr[i]);
            }   
        }
        else if(gameMode == 1){
            amountOfPanels = 225;
            TicTacToePanel[] panelArr = new TicTacToePanel[amountOfPanels];
            add(gamePanel, new GridLayout(15, 15));
            setPreferredSize(new Dimension(500, 500));
            for(int i = 0; i < amountOfPanels; i++){
                panelArr[i] = new TicTacToePanel();
                gamePanel.add(panelArr[i]);
            }
        }

    }

    public static void main(String[] args){
        JOptionPane.showMessageDialog(null, new TicTacToeGUI(0));
    }
}

Answer 1

If you're goal is to create a Tic Tac Toe game, then you may wish to re-think your current strategy of adding components to the GUI on the fly. Much better would be to create a grid of components, say of JLabel, and place them on the JPanel at program start up. This way you can change the pressed JLabel's text and color, and even its Icon if you want to be fancy during program run without having to add or remove components. For example:

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

@SuppressWarnings("serial")
public class TicTacToePanel extends JPanel {
    private static final int ROWS = 3;
    private static final int MY_C = 240;
    private static final Color BG = new Color(MY_C, MY_C, MY_C);
    private static final int PTS = 60;
    private static final Font FONT = new Font(Font.SANS_SERIF, Font.BOLD, PTS);
    public static final Color X_COLOR = Color.BLUE;
    public static final Color O_COLOR = Color.RED;
    private JLabel[][] labels = new JLabel[ROWS][ROWS];
    private boolean xTurn = true;

    public TicTacToePanel() {
        setLayout(new GridLayout(ROWS, ROWS, 2, 2));
        setBackground(Color.black);

        MyMouse myMouse = new MyMouse();
        for (int row = 0; row < labels.length; row++) {
            for (int col = 0; col < labels[row].length; col++) {
                JLabel label = new JLabel("     ", SwingConstants.CENTER);
                label.setOpaque(true);
                label.setBackground(BG);
                label.setFont(FONT);
                add(label);
                label.addMouseListener(myMouse);
            }
        }
    }

    private class MyMouse extends MouseAdapter {
        @Override // override mousePressed not mouseClicked
        public void mousePressed(MouseEvent e) {
            JLabel label = (JLabel) e.getSource();
            String text = label.getText().trim();
            if (!text.isEmpty()) {
                return;
            }
            if (xTurn) {
                label.setForeground(X_COLOR);
                label.setText("X");
            } else {
                label.setForeground(O_COLOR);
                label.setText("O");
            }

            // information to help check for win
            int chosenX = -1;
            int chosenY = -1;
            for (int x = 0; x < labels.length; x++) {
                for (int y = 0; y < labels[x].length; y++) {
                    if (labels[x][y] == label) {
                        chosenX = x;
                        chosenY = y;
                    }
                }
            }
            // TODO: check for win here
            xTurn = !xTurn;
        }
    }

    private static void createAndShowGui() {
        TicTacToePanel mainPanel = new TicTacToePanel();

        JFrame frame = new JFrame("Tic Tac Toe");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGui();
            }
        });
    }
}

Answer 2

When you add/remove components at runtime, always call revalidate() afterwards. revalidate() makes the component refresh/relayout.

So just call revalidate() after you add the label and it will work.