* #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