(feat) implement optional section on polymorphism

week23.java

@@ -286,3 +286,13 @@ class DemoSavingsAccount {
 
     }
 }
+
+class PolymorphismTest {
+    public static void main(String[] args) {
+        Person telemachus = new Person();
+        telemachus.setName("Τηλέμαχος");
+        BankAccount b = new SavingsAccount(telemachus, 10);
+
+        System.out.println(String.format("%s", b));
+    }
+}