diff --git a/dao/src/main/java/com/iluwatar/dao/DbCustomerDao.java b/dao/src/main/java/com/iluwatar/dao/DbCustomerDao.java
index 15f20eb43..23958cab9 100644
--- a/dao/src/main/java/com/iluwatar/dao/DbCustomerDao.java
+++ b/dao/src/main/java/com/iluwatar/dao/DbCustomerDao.java
@@ -67,7 +67,7 @@ public class DbCustomerDao implements CustomerDao {
   public Stream<Customer> getAll() throws Exception {
     try {
       var connection = getConnection();
-      var statement = connection.prepareStatement("SELECT * FROM CUSTOMERS");
+      var statement = connection.prepareStatement("SELECT * FROM CUSTOMERS"); // NOSONAR
       var resultSet = statement.executeQuery(); // NOSONAR
       return StreamSupport.stream(new Spliterators.AbstractSpliterator<Customer>(Long.MAX_VALUE,
           Spliterator.ORDERED) {
diff --git a/special-case/src/main/java/com/iluwatar/specialcase/Db.java b/special-case/src/main/java/com/iluwatar/specialcase/Db.java
index 7696e9865..4c6665fef 100644
--- a/special-case/src/main/java/com/iluwatar/specialcase/Db.java
+++ b/special-case/src/main/java/com/iluwatar/specialcase/Db.java
@@ -38,16 +38,13 @@ public class Db {
    *
    * @return singleton instance of Db class
    */
-  public static Db getInstance() {
+  public static synchronized Db getInstance() {
     if (instance == null) {
-      synchronized (Db.class) {
-        if (instance == null) {
-          instance = new Db();
-          instance.userName2User = new HashMap<>();
-          instance.user2Account = new HashMap<>();
-          instance.itemName2Product = new HashMap<>();
-        }
-      }
+      Db newInstance = new Db();
+      newInstance.userName2User = new HashMap<>();
+      newInstance.user2Account = new HashMap<>();
+      newInstance.itemName2Product = new HashMap<>();
+      instance = newInstance;
     }
     return instance;
   }
diff --git a/special-case/src/main/java/com/iluwatar/specialcase/MaintenanceLock.java b/special-case/src/main/java/com/iluwatar/specialcase/MaintenanceLock.java
index ffe0c2628..214e04d6b 100644
--- a/special-case/src/main/java/com/iluwatar/specialcase/MaintenanceLock.java
+++ b/special-case/src/main/java/com/iluwatar/specialcase/MaintenanceLock.java
@@ -38,13 +38,9 @@ public class MaintenanceLock {
    *
    * @return singleton instance of MaintenanceLock
    */
-  public static MaintenanceLock getInstance() {
+  public static synchronized MaintenanceLock getInstance() {
     if (instance == null) {
-      synchronized (MaintenanceLock.class) {
-        if (instance == null) {
-          instance = new MaintenanceLock();
-        }
-      }
+      instance = new MaintenanceLock();
     }
     return instance;
   }
@@ -55,6 +51,6 @@ public class MaintenanceLock {
 
   public void setLock(boolean lock) {
     this.lock = lock;
-    LOGGER.info("Maintenance lock is set to: " + lock);
+    LOGGER.info("Maintenance lock is set to: ", lock);
   }
 }
diff --git a/transaction-script/src/main/java/com/iluwatar/transactionscript/HotelDaoImpl.java b/transaction-script/src/main/java/com/iluwatar/transactionscript/HotelDaoImpl.java
index 240f96892..07c88b698 100644
--- a/transaction-script/src/main/java/com/iluwatar/transactionscript/HotelDaoImpl.java
+++ b/transaction-script/src/main/java/com/iluwatar/transactionscript/HotelDaoImpl.java
@@ -49,7 +49,7 @@ public class HotelDaoImpl implements HotelDao {
   public Stream<Room> getAll() throws Exception {
     try {
       var connection = getConnection();
-      var statement = connection.prepareStatement("SELECT * FROM ROOMS");
+      var statement = connection.prepareStatement("SELECT * FROM ROOMS"); // NOSONAR
       var resultSet = statement.executeQuery(); // NOSONAR
       return StreamSupport.stream(new Spliterators.AbstractSpliterator<Room>(Long.MAX_VALUE,
           Spliterator.ORDERED) {