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/pmd-doc-7.10.0/pmd_rules_java_design.html#classwithonlyprivateconstructorsshouldbefinal

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/pmd-doc-7.10.0/pmd_rules_java_design.html#classwithonlyprivateconstructorsshouldbefinal

Whenever using a log level, one should check if it is actually enabled, or otherwise skip the associate String creation and manipulation, as well as any method calls. An alternative to checking the log level are substituting parameters, formatters or lazy logging with lambdas. The available alternatives depend on the actual logging framework. GuardLogStatement (Priority: 2, Ruleset: Best Practices) https://docs.pmd-code.org/pmd-doc-7.10.0/pmd_rules_java_bestpractices.html#guardlogstatement

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/pmd-doc-7.10.0/pmd_rules_java_design.html#classwithonlyprivateconstructorsshouldbefinal

Whenever using a log level, one should check if it is actually enabled, or otherwise skip the associate String creation and manipulation, as well as any method calls. An alternative to checking the log level are substituting parameters, formatters or lazy logging with lambdas. The available alternatives depend on the actual logging framework. GuardLogStatement (Priority: 2, Ruleset: Best Practices) https://docs.pmd-code.org/pmd-doc-7.10.0/pmd_rules_java_bestpractices.html#guardlogstatement

Whenever using a log level, one should check if it is actually enabled, or otherwise skip the associate String creation and manipulation, as well as any method calls. An alternative to checking the log level are substituting parameters, formatters or lazy logging with lambdas. The available alternatives depend on the actual logging framework. GuardLogStatement (Priority: 2, Ruleset: Best Practices) https://docs.pmd-code.org/pmd-doc-7.10.0/pmd_rules_java_bestpractices.html#guardlogstatement

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Reports non-final fields whose value never changes once object initialization ends, and hence may be marked final. Note that this rule does not enforce that the field value be deeply immutable itself. An object can still have mutable state, even if all its member fields are declared final. This is referred to as shallow immutability. For more information on mutability, see *Effective Java, 3rd Edition, Item 17: Minimize mutability*. Limitations: We can only check private fields for now. ImmutableField (Priority: 3, Ruleset: Design) https://docs.pmd-code.org/pmd-doc-7.10.0/pmd_rules_java_design.html#immutablefield

Reports non-final fields whose value never changes once object initialization ends, and hence may be marked final. Note that this rule does not enforce that the field value be deeply immutable itself. An object can still have mutable state, even if all its member fields are declared final. This is referred to as shallow immutability. For more information on mutability, see *Effective Java, 3rd Edition, Item 17: Minimize mutability*. Limitations: We can only check private fields for now. ImmutableField (Priority: 3, Ruleset: Design) https://docs.pmd-code.org/pmd-doc-7.10.0/pmd_rules_java_design.html#immutablefield

Switch statements should be exhaustive, to make their control flow easier to follow. This can be achieved by adding a `default` case, or, if the switch is on an enum type, by ensuring there is one switch branch for each enum constant. This rule doesn't consider Switch Statements, that use Pattern Matching, since for these the compiler already ensures that all cases are covered. The same is true for Switch Expressions, which are also not considered by this rule. NonExhaustiveSwitch (Priority: 3, Ruleset: Best Practices) https://docs.pmd-code.org/pmd-doc-7.10.0/pmd_rules_java_bestpractices.html#nonexhaustiveswitch

Detects when a local variable is declared and/or assigned, but not used. Variables whose name starts with `ignored` or `unused` are filtered out. UnusedLocalVariable (Priority: 3, Ruleset: Best Practices) https://docs.pmd-code.org/pmd-doc-7.10.0/pmd_rules_java_bestpractices.html#unusedlocalvariable

Detects when a private field is declared and/or assigned a value, but not used. Since PMD 6.50.0 private fields are ignored, if the fields are annotated with any annotation or the enclosing class has any annotation. Annotations often enable a framework (such as dependency injection, mocking or e.g. Lombok) which use the fields by reflection or other means. This usage can't be detected by static code analysis. Previously these frameworks where explicitly allowed by listing their annotations in the property "ignoredAnnotations", but that turned out to be prone of false positive for any not explicitly considered framework. UnusedPrivateField (Priority: 3, Ruleset: Best Practices) https://docs.pmd-code.org/pmd-doc-7.10.0/pmd_rules_java_bestpractices.html#unusedprivatefield

Reports non-final fields whose value never changes once object initialization ends, and hence may be marked final. Note that this rule does not enforce that the field value be deeply immutable itself. An object can still have mutable state, even if all its member fields are declared final. This is referred to as shallow immutability. For more information on mutability, see *Effective Java, 3rd Edition, Item 17: Minimize mutability*. Limitations: We can only check private fields for now. ImmutableField (Priority: 3, Ruleset: Design) https://docs.pmd-code.org/pmd-doc-7.10.0/pmd_rules_java_design.html#immutablefield

The isEmpty() method on java.util.Collection is provided to determine if a collection has any elements. Comparing the value of size() to 0 does not convey intent as well as the isEmpty() method. UseCollectionIsEmpty (Priority: 3, Ruleset: Best Practices) https://docs.pmd-code.org/pmd-doc-7.10.0/pmd_rules_java_bestpractices.html#usecollectionisempty

The isEmpty() method on java.util.Collection is provided to determine if a collection has any elements. Comparing the value of size() to 0 does not convey intent as well as the isEmpty() method. UseCollectionIsEmpty (Priority: 3, Ruleset: Best Practices) https://docs.pmd-code.org/pmd-doc-7.10.0/pmd_rules_java_bestpractices.html#usecollectionisempty

The conversion of literals to strings by concatenating them with empty strings is inefficient. It is much better to use one of the type-specific `toString()` methods instead or `String.valueOf()`. AddEmptyString (Priority: 3, Ruleset: Performance) https://docs.pmd-code.org/pmd-doc-7.10.0/pmd_rules_java_performance.html#addemptystring