dependencies: #2449 bump maven-checkstyle-plugin from 3.1.0 to 3.2.0 + resolve chec… (#2464)

* #2449 bump maven-checkstyle-plugin from 3.1.0 to 3.2.0 + resolve checkstyle issues

* remove FileSelectorJFrame.java to resolve checkstyle issue

* remove FileSelectorJFrame.java to resolve checkstyle issue

* remove FileSelectorJFrame.java to resolve checkstyle issue

* add refactored file with correct filename to resolve checkstyle issue

* add the test data

* change filenames from JFrame to Jframe for checkstyle

* fix code smell from  sonar report

* add new testcases to improve the test coverage

* remove code smell

registry/src/main/java/com/iluwatar/registry/App.java

@@ -27,6 +27,13 @@ package com.iluwatar.registry;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+/**
+ * In Registry pattern, objects of a single class are stored and provide a global point of access to them.
+ * Note that there is no restriction on the number of objects.
+ * 
+ * <p> The given example {@link CustomerRegistry} represents the registry used to store and
+ * access {@link Customer} objects. </p>
+ */
 public class App {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(App.class);

registry/src/main/java/com/iluwatar/registry/Customer.java

@@ -24,6 +24,9 @@
  */
 package com.iluwatar.registry;
 
+/**
+ * Customer entity used in registry pattern example.
+ */
 public class Customer {
 
   private final String id;

registry/src/main/java/com/iluwatar/registry/CustomerRegistry.java

@@ -27,6 +27,9 @@ package com.iluwatar.registry;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 
+/**
+ * CustomerRegistry class used to store/access {@link Customer} objects.
+ */
 public final class CustomerRegistry {
 
   private static final CustomerRegistry instance = new CustomerRegistry();