If an abstract class does not provide any methods, it may be acting as a simple data container that is not meant to be instantiated. In this case, it is probably better to use a private or protected constructor in order to prevent instantiation than make the class misleadingly abstract. AbstractClassWithoutAnyMethod (Priority: 1, Ruleset: Design) https://docs.pmd-code.org/pmd-doc-7.6.0/pmd_rules_java_design.html#abstractclasswithoutanymethod

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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-7.6.0/pmd_rules_java_bestpractices.html#unusedprivatefield

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-7.6.0/pmd_rules_java_bestpractices.html#unusedprivatefield

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-7.6.0/pmd_rules_java_bestpractices.html#unusedprivatefield