diff --git a/src/main/java/edu/group5/app/model/donation/DonationService.java b/src/main/java/edu/group5/app/model/donation/DonationService.java
index ecd13da..6f12f91 100644
--- a/src/main/java/edu/group5/app/model/donation/DonationService.java
+++ b/src/main/java/edu/group5/app/model/donation/DonationService.java
@@ -8,34 +8,55 @@
 import edu.group5.app.model.user.Customer;
 import edu.group5.app.model.donation.DonationRepository;
 
+/**
+ * DonationService class provides functionality for handling donations in the system.
+ * It interacts with the DonationRepository to manage donation records 
+ * and the OrganizationRepository to validate organization information.
+ * The donate method allows a customer to make a donation to a specified organization,
+ * ensuring that the customer, organization, and donation amount are valid before processing the donation.
+ */
 public class DonationService {
 
   private final DonationRepository donationRepository;
   private final OrganizationRepository organizationRepository;
 
+  /**
+   * Constructor for DonationService. Initializes the service with the required repositories.
+   * @param donationRepository the repository for managing donation records
+   * @param organizationRepository the repository for managing organization information
+   * @throws IllegalArgumentException if either repository is null
+   */
   public DonationService(DonationRepository donationRepository,
                         OrganizationRepository organizationRepository) {
-      this.donationRepository = donationRepository;
-      this.organizationRepository = organizationRepository;
+    if (donationRepository == null) {
+      throw new IllegalArgumentException("DonationRepository cannot be null");
+    }
+    if (organizationRepository == null) {
+      throw new IllegalArgumentException("OrganizationRepository cannot be null");
+    }
+    this.donationRepository = donationRepository;
+    this.organizationRepository = organizationRepository;
   }
 
-    public boolean donate(Customer customer,
-                          int orgNumber,
-                          BigDecimal amount) {
-        if (customer == null || amount == null || amount.compareTo(BigDecimal.ZERO) <= 0) {
-            return false;
-        }
-        Organization org = organizationRepository.findByOrgNumber(orgNumber);
-        if (org == null) {
-            return false;
-        }
-        Donation donation = new Donation(
-                customer.getUserId(),
-                org.getOrgNumber(),
-                amount,
-                new Timestamp(System.currentTimeMillis())
-        );
-        donationRepository.addDonation(donation);
-        return true;
+  /**
+   * Processes a donation from a customer to a specified organization with a given amount.
+   * Validates the customer, organization number, and donation amount before creating a donation record.
+   * @param customer the customer making the donation
+   * @param orgNumber the organization number to which the donation is made
+   * @param amount the amount of the donation
+   * @return true if the donation is successfully processed, false otherwise
+   */
+  public boolean donate(Customer customer, int orgNumber, BigDecimal amount) {
+    if (customer == null || amount == null || amount.compareTo(BigDecimal.ZERO) <= 0) {
+      return false;
     }
+    Organization org = organizationRepository.findByOrgNumber(orgNumber);
+    if (org == null) {
+      return false;
+    }
+    Donation donation = new Donation(customer.getUserId(), org.getOrgNumber(),
+                  amount, new Timestamp(System.currentTimeMillis()));
+    donationRepository.addDonation(donation);
+    return true;
+  }
 }
\ No newline at end of file
diff --git a/src/main/java/edu/group5/app/model/user/Customer.java b/src/main/java/edu/group5/app/model/user/Customer.java
index 4f52b19..6ae6109 100644
--- a/src/main/java/edu/group5/app/model/user/Customer.java
+++ b/src/main/java/edu/group5/app/model/user/Customer.java
@@ -36,17 +36,35 @@ public List<Integer> getPreferences() {
     return preferences;
   }
 
-  public void addPreference(int orgNumber) {
-    if (preferences.contains(orgNumber)) {
-      throw new IllegalArgumentException("Organization number already in preferences");
+  public boolean addPreference(int orgNumber) {
+    try {
+      if (orgNumber <= 0) {
+        throw new IllegalArgumentException("Organization number must be a positive integer");
+      }
+      if (preferences.contains(orgNumber)) {
+        throw new IllegalStateException("Organization number already in preferences");
+      }
+      preferences.add(orgNumber);
+      return true;
+    } catch (Exception e) {
+      System.out.println("Add preference failed: " + e.getMessage());
+      return false;
     }
-    preferences.add(orgNumber);
   }
 
-  public void removePreference(int orgNumber) {
-    if (!preferences.contains(orgNumber)) {
-      throw new IllegalArgumentException("Organization number not found in preferences");
+  public boolean removePreference(int orgNumber) {
+    try {
+      if (orgNumber <= 0) {
+        throw new IllegalArgumentException("Organization number must be a positive integer");
+      }
+      if (!preferences.contains(orgNumber)) {
+        throw new IllegalStateException("Organization number not found in preferences");
+      }
+      preferences.remove(Integer.valueOf(orgNumber));
+      return true;
+    } catch (Exception e) {
+      System.out.println("Remove preference failed: " + e.getMessage());
+      return false;
     }
-    preferences.remove(Integer.valueOf(orgNumber));
   }
-}
\ No newline at end of file
+}