finish Q5d

src/Ball.java

@@ -48,6 +48,18 @@ public class Ball {
     }
 
     public void update() {
+        // (d) Extend the code to make the ball choose a random diagonal direction, and move in that direction.
+        //  - When the ball reaches the left and right edges of the window, it should reverse horizontal direction.
+        //  - Similarly, when the ball reaches the top and bottom edges of the window, it should reverse vertical direction.
+        //      You can change the step size of player and ball when simulating.
+        // When the ball reaches the left and right edges of the window, it should reverse horizontal direction.
+        if (x < 0 || x > Window.getWidth()) {
+            directionX *= -1;
+        }
+        // Similarly, when the ball reaches the top and bottom edges of the window, it should reverse vertical direction.
+        if (y < 0 || y > Window.getHeight()) {
+            directionY *= -1;
+        }
 
         // (a)
         x += directionX * STEP_SIZE;