Java allows the use of several variables declaration of the same type on one line. However, it can lead to quite messy code. This rule looks for several declarations on the same line. OneDeclarationPerLine (Priority: 4, Ruleset: Best Practices) https://docs.pmd-code.org/pmd-doc-7.7.0/pmd_rules_java_bestpractices.html#onedeclarationperline

Java allows the use of several variables declaration of the same type on one line. However, it can lead to quite messy code. This rule looks for several declarations on the same line. OneDeclarationPerLine (Priority: 4, Ruleset: Best Practices) https://docs.pmd-code.org/pmd-doc-7.7.0/pmd_rules_java_bestpractices.html#onedeclarationperline

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: 3, Ruleset: Design) https://docs.pmd-code.org/pmd-doc-7.7.0/pmd_rules_java_design.html#singularfield

Java will initialize fields with known default values so any explicit initialization of those same defaults is redundant and results in a larger class file (approximately three additional bytecode instructions per field). RedundantFieldInitializer (Priority: 3, Ruleset: Performance) https://docs.pmd-code.org/pmd-doc-7.7.0/pmd_rules_java_performance.html#redundantfieldinitializer

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-7.7.0/pmd_rules_java_design.html#immutablefield

Java will initialize fields with known default values so any explicit initialization of those same defaults is redundant and results in a larger class file (approximately three additional bytecode instructions per field). RedundantFieldInitializer (Priority: 3, Ruleset: Performance) https://docs.pmd-code.org/pmd-doc-7.7.0/pmd_rules_java_performance.html#redundantfieldinitializer

Java will initialize fields with known default values so any explicit initialization of those same defaults is redundant and results in a larger class file (approximately three additional bytecode instructions per field). RedundantFieldInitializer (Priority: 3, Ruleset: Performance) https://docs.pmd-code.org/pmd-doc-7.7.0/pmd_rules_java_performance.html#redundantfieldinitializer

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-7.7.0/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-7.7.0/pmd_rules_java_bestpractices.html#usecollectionisempty