diff --git a/src/main/java/hs/fulda/de/ci/exam/project/FlightReservationRepository.java b/src/main/java/hs/fulda/de/ci/exam/project/FlightReservationRepository.java
index 5a1a071..c169649 100644
--- a/src/main/java/hs/fulda/de/ci/exam/project/FlightReservationRepository.java
+++ b/src/main/java/hs/fulda/de/ci/exam/project/FlightReservationRepository.java
@@ -1,8 +1,36 @@
 package hs.fulda.de.ci.exam.project;
 
-import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+public class FlightReservationRepository {
+    Map<String, FlightReservation> flightReservationList = new ConcurrentHashMap<String, FlightReservation>();
+
+    public boolean checkIfFlightAlreadyExist(FlightReservation flightReservation){
+        if(flightReservationList.containsKey(generateKey(flightReservation))){
+            return true;
+        }
+        return false;
+    }
+    FlightReservation findById(String id){
+        FlightReservation flightReservation = flightReservationList.get(id);
+        return flightReservation;
+    }
+
+    private String generateKey(FlightReservation flightReservation) {
+        return String.format("%s", flightReservation.getReservationNumber());
+    }
+    public Collection<FlightReservation> findAll() {
+        return  flightReservationList.values();
+    }
+    public boolean save(FlightReservation flightReservation){
+        flightReservationList.put(generateKey(flightReservation), flightReservation);
+        return true;
+    }
+
+    public void delete(FlightReservation flightReservation) {
+        flightReservationList.remove(generateKey(flightReservation));
+    }
 
-public interface FlightReservationRepository {
-    ArrayList<FlightReservation> findAll();
-    void save(FlightReservation flightReservation);
 }