diff --git a/app/src/main/java/fr/romanet/vj/apps/myweather/AddCity.java b/app/src/main/java/fr/romanet/vj/apps/myweather/AddCity.java
index e8d466d..7df5ab3 100644
--- a/app/src/main/java/fr/romanet/vj/apps/myweather/AddCity.java
+++ b/app/src/main/java/fr/romanet/vj/apps/myweather/AddCity.java
@@ -3,19 +3,21 @@ package fr.romanet.vj.apps.myweather;
 import androidx.appcompat.app.AppCompatActivity;
 import androidx.appcompat.widget.Toolbar;
 
-import android.content.Context;
 import android.content.Intent;
-import android.content.SharedPreferences;
 import android.os.Bundle;
 import android.view.View;
 import android.widget.Button;
 import android.widget.EditText;
+
+import java.util.List;
+
 import fr.romanet.vj.apps.myweather.bo.City;
 import fr.romanet.vj.apps.myweather.repository.CityRepository;
 
 public class AddCity extends AppCompatActivity {
 
     private EditText cityName;
+    private Toolbar toolbarAddCity;
 
     @Override
     protected void onCreate(Bundle savedInstanceState)
@@ -23,9 +25,10 @@ public class AddCity extends AppCompatActivity {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.add_city_page);
 
-        Toolbar toolbarAddCity = (Toolbar) findViewById(R.id.toolbarAddCity);
+        toolbarAddCity = (Toolbar) findViewById(R.id.toolbarAddCity);
         setSupportActionBar(toolbarAddCity);
 
+        //Ading the arrow back functionnality in the toolbar
         getSupportActionBar().setDisplayHomeAsUpEnabled(true);
         getSupportActionBar().setDisplayShowHomeEnabled(true);
 
@@ -34,32 +37,59 @@ public class AddCity extends AppCompatActivity {
         {
             public void onClick(View v)
             {
+                //When the save button is clicked, we display an error message if the editable text is empty or, we save the data into the database
                 cityName =  (EditText) findViewById(R.id.editTextNewCity);
                 final String newCityString = cityName.getEditableText().toString();
+                boolean exist = existOrNot(newCityString);
                 if(newCityString.isEmpty())
                 {
                     cityName.setError("Please, enter a city name");
                 }
+                else if(exist)
+                {
+                    cityName.setError("Please, enter a city name that is not in your favorite");
+                    resetForm();
+                }
                 else {
                     saveCity(newCityString);
                     resetForm();
-                    openAddCityPage();
+                    openMainActivity();
                 }
             }
         });
     }
 
+    //Method that reset the form to a blank editable text
     private void resetForm()
     {
         cityName.setText(null);
     }
 
+    /**
+     * Method that allows us to save a city into the database by calling a method from the repository
+     * @param cityName : the city to save
+     */
     private void saveCity(String cityName)
     {
         CityRepository.getInstance(this).addCity(new City(cityName));
     }
 
-    public void openAddCityPage()
+    public boolean existOrNot(String nameOfCity)
+    {
+        boolean exist = false;
+        final List<City> city = CityRepository.getInstance(this).getCity();
+        for(int i = 0; i < city.size(); i++)
+        {
+            if(city.get(i).nameCity.equals(nameOfCity))
+            {
+                exist = true;
+            }
+        }
+        return exist;
+    }
+
+    //Calling the main activity screen
+    public void openMainActivity()
     {
         Intent intent = new Intent(AddCity.this, MainActivity.class);
         startActivity(intent);
diff --git a/app/src/main/java/fr/romanet/vj/apps/myweather/bo/City.java b/app/src/main/java/fr/romanet/vj/apps/myweather/bo/City.java
index 13d7b51..f7a892f 100644
--- a/app/src/main/java/fr/romanet/vj/apps/myweather/bo/City.java
+++ b/app/src/main/java/fr/romanet/vj/apps/myweather/bo/City.java
@@ -24,9 +24,12 @@ final public class City implements Serializable
         @Override
         public int compare(City o1, City o2)
         {
-            return o1.nameCity.compareTo(o2.nameCity);
+            if(o1.id == o2.id)
+            {
+                return 0;
+            }
+            else return 1;
         }
-
     }
 
     /**