add interface

src/java/lodge/reservationsystem/IReservation.java

@@ -0,0 +1,9 @@
+package lodge.reservationsystem;
+
+public interface IReservation {
+    
+    public String ReservationType();
+    public boolean checkValid() throws ReservationException;
+    public float calculatePrice();
+
+}

src/java/lodge/reservationsystem/Reservation.java

@@ -8,7 +8,7 @@ import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.time.ZonedDateTime;
 
-public abstract class Reservation {
+public abstract class Reservation implements IReservation{
     private char type;
     private String reservation_number = "-99";
     private Address physical_address;
@@ -240,13 +240,8 @@ public abstract class Reservation {
         }
     }
 
-    public abstract String ReservationType();
-
-    public abstract float calculatePrice();
-
-    public abstract boolean checkValid() throws ReservationException;
-
     public void update(Reservation rsrv) {
 
     }
+
 }