Code cleanup (#12333)

Code cleanup (#12333)

- removed unused private methods
- removed unused private variables
- removed unnecessary initializations
- removed unnecessary substring(0)
- removed inner assignments
- renamed private methods that started with upper case
- renamed static final variables to use upper case
- converted to use non-deprecated options
- suppressed unavoidable warnings
- divided long Strings to multiple lines
- added missing types
- added missing JavaDoc parameters
- formatting
- updated comments & JavaDocs