squid:S2974 - Classes without public constructors should be final

singleton/src/main/java/com/iluwatar/singleton/InitializingOnDemandHolderIdiom.java

@@ -34,7 +34,7 @@ import java.io.Serializable;
  *
  * @author mortezaadi@gmail.com
  */
-public class InitializingOnDemandHolderIdiom implements Serializable {
+public final class InitializingOnDemandHolderIdiom implements Serializable {
 
   private static final long serialVersionUID = 1L;
 

singleton/src/main/java/com/iluwatar/singleton/ThreadSafeDoubleCheckLocking.java

@@ -31,7 +31,7 @@ package com.iluwatar.singleton;
  *
  * @author mortezaadi@gmail.com
  */
-public class ThreadSafeDoubleCheckLocking {
+public final class ThreadSafeDoubleCheckLocking {
 
   private static volatile ThreadSafeDoubleCheckLocking instance;
 

singleton/src/main/java/com/iluwatar/singleton/ThreadSafeLazyLoadedIvoryTower.java

@@ -29,7 +29,7 @@ package com.iluwatar.singleton;
  * Note: if created by reflection then a singleton will not be created but multiple options in the
  * same classloader
  */
-public class ThreadSafeLazyLoadedIvoryTower {
+public final class ThreadSafeLazyLoadedIvoryTower {
 
   private static ThreadSafeLazyLoadedIvoryTower instance = null;