For any method that returns an collection (such as an array, Collection or Map), it is better to return an empty one rather than a null reference. This removes the need for null checking all results and avoids inadvertent NullPointerExceptions. See Effective Java, 3rd Edition, Item 54: Return empty collections or arrays instead of null ReturnEmptyCollectionRatherThanNull (Priority: 1, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.4.0/pmd_rules_java_errorprone.html#returnemptycollectionratherthannull

For any method that returns an collection (such as an array, Collection or Map), it is better to return an empty one rather than a null reference. This removes the need for null checking all results and avoids inadvertent NullPointerExceptions. See Effective Java, 3rd Edition, Item 54: Return empty collections or arrays instead of null ReturnEmptyCollectionRatherThanNull (Priority: 1, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.4.0/pmd_rules_java_errorprone.html#returnemptycollectionratherthannull

For any method that returns an collection (such as an array, Collection or Map), it is better to return an empty one rather than a null reference. This removes the need for null checking all results and avoids inadvertent NullPointerExceptions. See Effective Java, 3rd Edition, Item 54: Return empty collections or arrays instead of null ReturnEmptyCollectionRatherThanNull (Priority: 1, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.4.0/pmd_rules_java_errorprone.html#returnemptycollectionratherthannull

For any method that returns an collection (such as an array, Collection or Map), it is better to return an empty one rather than a null reference. This removes the need for null checking all results and avoids inadvertent NullPointerExceptions. See Effective Java, 3rd Edition, Item 54: Return empty collections or arrays instead of null ReturnEmptyCollectionRatherThanNull (Priority: 1, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.4.0/pmd_rules_java_errorprone.html#returnemptycollectionratherthannull

Configurable naming conventions for formal parameters of methods and lambdas. This rule reports formal parameters which do not match the regex that applies to their specific kind (e.g. lambda parameter, or final formal parameter). Each regex can be configured through properties. By default this rule uses the standard Java naming convention (Camel case). FormalParameterNamingConventions (Priority: 1, Ruleset: Code Style) https://docs.pmd-code.org/pmd-doc-7.4.0/pmd_rules_java_codestyle.html#formalparameternamingconventions

Configurable naming conventions for local variable declarations and other locally-scoped variables. This rule reports variable declarations which do not match the regex that applies to their specific kind (e.g. final variable, or catch-clause parameter). Each regex can be configured through properties. By default this rule uses the standard Java naming convention (Camel case). LocalVariableNamingConventions (Priority: 1, Ruleset: Code Style) https://docs.pmd-code.org/pmd-doc-7.4.0/pmd_rules_java_codestyle.html#localvariablenamingconventions

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-7.4.0/pmd_rules_java_design.html#classwithonlyprivateconstructorsshouldbefinal

For any method that returns an collection (such as an array, Collection or Map), it is better to return an empty one rather than a null reference. This removes the need for null checking all results and avoids inadvertent NullPointerExceptions. See Effective Java, 3rd Edition, Item 54: Return empty collections or arrays instead of null ReturnEmptyCollectionRatherThanNull (Priority: 1, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.4.0/pmd_rules_java_errorprone.html#returnemptycollectionratherthannull

For any method that returns an collection (such as an array, Collection or Map), it is better to return an empty one rather than a null reference. This removes the need for null checking all results and avoids inadvertent NullPointerExceptions. See Effective Java, 3rd Edition, Item 54: Return empty collections or arrays instead of null ReturnEmptyCollectionRatherThanNull (Priority: 1, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.4.0/pmd_rules_java_errorprone.html#returnemptycollectionratherthannull

For any method that returns an collection (such as an array, Collection or Map), it is better to return an empty one rather than a null reference. This removes the need for null checking all results and avoids inadvertent NullPointerExceptions. See Effective Java, 3rd Edition, Item 54: Return empty collections or arrays instead of null ReturnEmptyCollectionRatherThanNull (Priority: 1, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.4.0/pmd_rules_java_errorprone.html#returnemptycollectionratherthannull

Excessive coupling to implementation types (e.g., `HashSet`) limits your ability to use alternate implementations in the future as requirements change. Whenever available, declare variables and parameters using a more general type (e.g, `Set`). This rule reports uses of concrete collection types. User-defined types that should be treated the same as interfaces can be configured with the property `allowedTypes`. LooseCoupling (Priority: 3, Ruleset: Best Practices) https://docs.pmd-code.org/pmd-doc-7.4.0/pmd_rules_java_bestpractices.html#loosecoupling

Excessive coupling to implementation types (e.g., `HashSet`) limits your ability to use alternate implementations in the future as requirements change. Whenever available, declare variables and parameters using a more general type (e.g, `Set`). This rule reports uses of concrete collection types. User-defined types that should be treated the same as interfaces can be configured with the property `allowedTypes`. LooseCoupling (Priority: 3, Ruleset: Best Practices) https://docs.pmd-code.org/pmd-doc-7.4.0/pmd_rules_java_bestpractices.html#loosecoupling

Reports import statements that can be removed. They are either unused, duplicated, or the members they import are already implicitly in scope, because they're in java.lang, or the current package. If some imports cannot be resolved, for instance because you run PMD with an incomplete auxiliary classpath, some imports may be conservatively marked as used even if they're not to avoid false positives. UnnecessaryImport (Priority: 4, Ruleset: Code Style) https://docs.pmd-code.org/pmd-doc-7.4.0/pmd_rules_java_codestyle.html#unnecessaryimport

Excessive coupling to implementation types (e.g., `HashSet`) limits your ability to use alternate implementations in the future as requirements change. Whenever available, declare variables and parameters using a more general type (e.g, `Set`). This rule reports uses of concrete collection types. User-defined types that should be treated the same as interfaces can be configured with the property `allowedTypes`. LooseCoupling (Priority: 3, Ruleset: Best Practices) https://docs.pmd-code.org/pmd-doc-7.4.0/pmd_rules_java_bestpractices.html#loosecoupling

Excessive coupling to implementation types (e.g., `HashSet`) limits your ability to use alternate implementations in the future as requirements change. Whenever available, declare variables and parameters using a more general type (e.g, `Set`). This rule reports uses of concrete collection types. User-defined types that should be treated the same as interfaces can be configured with the property `allowedTypes`. LooseCoupling (Priority: 3, Ruleset: Best Practices) https://docs.pmd-code.org/pmd-doc-7.4.0/pmd_rules_java_bestpractices.html#loosecoupling

Excessive coupling to implementation types (e.g., `HashSet`) limits your ability to use alternate implementations in the future as requirements change. Whenever available, declare variables and parameters using a more general type (e.g, `Set`). This rule reports uses of concrete collection types. User-defined types that should be treated the same as interfaces can be configured with the property `allowedTypes`. LooseCoupling (Priority: 3, Ruleset: Best Practices) https://docs.pmd-code.org/pmd-doc-7.4.0/pmd_rules_java_bestpractices.html#loosecoupling

Reports import statements that can be removed. They are either unused, duplicated, or the members they import are already implicitly in scope, because they're in java.lang, or the current package. If some imports cannot be resolved, for instance because you run PMD with an incomplete auxiliary classpath, some imports may be conservatively marked as used even if they're not to avoid false positives. UnnecessaryImport (Priority: 4, Ruleset: Code Style) https://docs.pmd-code.org/pmd-doc-7.4.0/pmd_rules_java_codestyle.html#unnecessaryimport

Avoid unnecessary if-then-else statements when returning a boolean. The result of the conditional test can be returned instead. SimplifyBooleanReturns (Priority: 3, Ruleset: Design) https://docs.pmd-code.org/pmd-doc-7.4.0/pmd_rules_java_design.html#simplifybooleanreturns

Parenthesized expressions are used to override the default operator precedence rules. Parentheses whose removal would not change the relative nesting of operators are unnecessary, because they don't change the semantics of the enclosing expression. Some parentheses that strictly speaking are unnecessary, may still be considered useful for readability. This rule allows to ignore violations on two kinds of unnecessary parentheses: - "Clarifying" parentheses, which separate operators of difference precedence. While unnecessary, they make precedence rules explicit, which may be useful for rarely used operators. For example: ```java (a + b) & c // is equivalent to `a + b & c`, but probably clearer ``` Unset the property `ignoreClarifying` to report them. - "Balancing" parentheses, which are unnecessary but visually balance out another pair of parentheses around an equality operator. For example, those two expressions are equivalent: ```java (a == null) != (b == null) a == null != (b == null) ``` The parentheses on the right are required, and the parentheses on the left are just more visually pleasing. Unset the property `ignoreBalancing` to report them. UselessParentheses (Priority: 4, Ruleset: Code Style) https://docs.pmd-code.org/pmd-doc-7.4.0/pmd_rules_java_codestyle.html#uselessparentheses