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

separated-interface/src/main/java/com/iluwatar/separatedinterface/invoice/TaxCalculator.java

@@ -24,6 +24,9 @@
  */
 package com.iluwatar.separatedinterface.invoice;
 
+/**
+ * TaxCalculator interface to demonstrate The Separated Interface pattern.
+ */
 public interface TaxCalculator {
 
   double calculate(double amount);

separated-interface/src/test/java/com/iluwatar/separatedinterface/AppTest.java

@@ -25,7 +25,6 @@
 package com.iluwatar.separatedinterface;
 
 import org.junit.jupiter.api.Test;
-
 import com.iluwatar.separatedinterface.App;
 
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;