add condition for game over

src/main/java/com/example/tictactoe_game/TicTacToeFX.java

@@ -16,6 +16,8 @@ public class TicTacToeFX extends Application {
 
     private boolean isXTurn = true;
 
+    private boolean isGameOver = false;
+
     @Override
     public void start(Stage primaryStage) {
 
@@ -64,16 +66,18 @@ public class TicTacToeFX extends Application {
     }
 
     private void handleButtonClick(Button button) {
-        if(button.getText().isEmpty()) {
+        if(button.getText().isEmpty() && !this.isGameOver) {
             if (this.isXTurn) {
                 button.setText("X");
             } else {
                 button.setText("O");
             }
             if (checkForWin()) {
+                this.isGameOver = true;
                 button.fireEvent(new GameEvent(GameEvent.VICTORY_EVENT));
             }
             else if(checkForDraw()){
+                this.isGameOver = true;
                 button.fireEvent(new GameEvent(GameEvent.DRAW_EVENT));
             }