Uncommented Empty Constructor finds instances where a constructor does not contain statements, but there is no comment. By explicitly commenting empty constructors it is easier to distinguish between intentional (commented) and unintentional empty constructors. UncommentedEmptyConstructor (Priority: 1, Ruleset: Documentation) https://docs.pmd-code.org/pmd-doc-7.13.0/pmd_rules_java_documentation.html#uncommentedemptyconstructor

This rule detects when a constructor is not necessary; i.e., when there is only one constructor and the constructor is identical to the default constructor. The default constructor should has same access modifier as the declaring class. In an enum type, the default constructor is implicitly private. UnnecessaryConstructor (Priority: 1, Ruleset: Code Style) https://docs.pmd-code.org/pmd-doc-7.13.0/pmd_rules_java_codestyle.html#unnecessaryconstructor

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