Reports classes that may be made final because they cannot be extended from outside their compilation unit anyway. This is because all their constructors are private, so a subclass could not call the super constructor. ClassWithOnlyPrivateConstructorsShouldBeFinal (Priority: 1, Ruleset: Design) https://docs.pmd-code.org/snapshot/pmd_rules_java_design.html#classwithonlyprivateconstructorsshouldbefinal

Reports fields which may be converted to a local variable. This is so because in every method where the field is used, it is assigned before it is first read. Hence, the value that the field had before the method call may not be observed, so it might as well not be stored in the enclosing object. Limitations: * We can only check private fields for now. * The rule is not aware of threading, so it may cause false positives in concurrent code. Such FPs are best handled by suppression (see also the `ignoredAnnotations` property). SingularField (Priority: 1, Ruleset: Design) https://docs.pmd-code.org/snapshot/pmd_rules_java_design.html#singularfield

Reports classes that may be made final because they cannot be extended from outside their compilation unit anyway. This is because all their constructors are private, so a subclass could not call the super constructor. ClassWithOnlyPrivateConstructorsShouldBeFinal (Priority: 1, Ruleset: Design) https://docs.pmd-code.org/snapshot/pmd_rules_java_design.html#classwithonlyprivateconstructorsshouldbefinal