update

src/main/java/PingPong/GamePanel.java

@@ -56,6 +56,10 @@ public class GamePanel extends JPanel implements Runnable {
             paddle_2.pressed(e);
         }
     }
+    public void keyReleased(KeyEvent e) {
+        paddle_1.released(e);
+        paddle_2.released(e);
+    }
 
 
 

src/main/java/PingPong/Paddle.java

@@ -9,4 +9,7 @@ public class Paddle {
 
     public void pressed(KeyEvent e) {
     }
+
+    public void released(KeyEvent e) {
+    }
 }