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Some classes contain overloaded getInstance. The problem with overloaded getInstance methods is that the instance created using the overloaded method is not cached and so, for each call and new objects will be created for every invocation. SingleMethodSingleton (Priority: 2, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.9.0/pmd_rules_java_errorprone.html#singlemethodsingleton

A singleton class should only ever have one instance. Failure to check whether an instance has already been created may result in multiple instances being created. SingletonClassReturningNewInstance (Priority: 2, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.9.0/pmd_rules_java_errorprone.html#singletonclassreturningnewinstance

Reports calls to overridable methods on `this` during object initialization. These are invoked on an incompletely constructed object and can be difficult to debug if overridden. This is because the subclass usually assumes that the superclass is completely initialized in all methods. If that is not the case, bugs can appear in the constructor, for instance, some fields that are still null may cause a NullPointerException or be stored somewhere else to blow up later. To avoid this problem, only use methods that are static, private, or final in constructors. Note that those methods also must not call overridable methods transitively to be safe. ConstructorCallsOverridableMethod (Priority: 1, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.9.0/pmd_rules_java_errorprone.html#constructorcallsoverridablemethod

Reports calls to overridable methods on `this` during object initialization. These are invoked on an incompletely constructed object and can be difficult to debug if overridden. This is because the subclass usually assumes that the superclass is completely initialized in all methods. If that is not the case, bugs can appear in the constructor, for instance, some fields that are still null may cause a NullPointerException or be stored somewhere else to blow up later. To avoid this problem, only use methods that are static, private, or final in constructors. Note that those methods also must not call overridable methods transitively to be safe. ConstructorCallsOverridableMethod (Priority: 1, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.9.0/pmd_rules_java_errorprone.html#constructorcallsoverridablemethod

Reports calls to overridable methods on `this` during object initialization. These are invoked on an incompletely constructed object and can be difficult to debug if overridden. This is because the subclass usually assumes that the superclass is completely initialized in all methods. If that is not the case, bugs can appear in the constructor, for instance, some fields that are still null may cause a NullPointerException or be stored somewhere else to blow up later. To avoid this problem, only use methods that are static, private, or final in constructors. Note that those methods also must not call overridable methods transitively to be safe. ConstructorCallsOverridableMethod (Priority: 1, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.9.0/pmd_rules_java_errorprone.html#constructorcallsoverridablemethod

Reports calls to overridable methods on `this` during object initialization. These are invoked on an incompletely constructed object and can be difficult to debug if overridden. This is because the subclass usually assumes that the superclass is completely initialized in all methods. If that is not the case, bugs can appear in the constructor, for instance, some fields that are still null may cause a NullPointerException or be stored somewhere else to blow up later. To avoid this problem, only use methods that are static, private, or final in constructors. Note that those methods also must not call overridable methods transitively to be safe. ConstructorCallsOverridableMethod (Priority: 1, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.9.0/pmd_rules_java_errorprone.html#constructorcallsoverridablemethod

Reports calls to overridable methods on `this` during object initialization. These are invoked on an incompletely constructed object and can be difficult to debug if overridden. This is because the subclass usually assumes that the superclass is completely initialized in all methods. If that is not the case, bugs can appear in the constructor, for instance, some fields that are still null may cause a NullPointerException or be stored somewhere else to blow up later. To avoid this problem, only use methods that are static, private, or final in constructors. Note that those methods also must not call overridable methods transitively to be safe. ConstructorCallsOverridableMethod (Priority: 1, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.9.0/pmd_rules_java_errorprone.html#constructorcallsoverridablemethod

Reports calls to overridable methods on `this` during object initialization. These are invoked on an incompletely constructed object and can be difficult to debug if overridden. This is because the subclass usually assumes that the superclass is completely initialized in all methods. If that is not the case, bugs can appear in the constructor, for instance, some fields that are still null may cause a NullPointerException or be stored somewhere else to blow up later. To avoid this problem, only use methods that are static, private, or final in constructors. Note that those methods also must not call overridable methods transitively to be safe. ConstructorCallsOverridableMethod (Priority: 1, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.9.0/pmd_rules_java_errorprone.html#constructorcallsoverridablemethod

Reports calls to overridable methods on `this` during object initialization. These are invoked on an incompletely constructed object and can be difficult to debug if overridden. This is because the subclass usually assumes that the superclass is completely initialized in all methods. If that is not the case, bugs can appear in the constructor, for instance, some fields that are still null may cause a NullPointerException or be stored somewhere else to blow up later. To avoid this problem, only use methods that are static, private, or final in constructors. Note that those methods also must not call overridable methods transitively to be safe. ConstructorCallsOverridableMethod (Priority: 1, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.9.0/pmd_rules_java_errorprone.html#constructorcallsoverridablemethod

Reports calls to overridable methods on `this` during object initialization. These are invoked on an incompletely constructed object and can be difficult to debug if overridden. This is because the subclass usually assumes that the superclass is completely initialized in all methods. If that is not the case, bugs can appear in the constructor, for instance, some fields that are still null may cause a NullPointerException or be stored somewhere else to blow up later. To avoid this problem, only use methods that are static, private, or final in constructors. Note that those methods also must not call overridable methods transitively to be safe. ConstructorCallsOverridableMethod (Priority: 1, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.9.0/pmd_rules_java_errorprone.html#constructorcallsoverridablemethod

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Position literals first in all String comparisons, if the second argument is null then NullPointerExceptions can be avoided, they will just return false. Note that switching literal positions for compareTo and compareToIgnoreCase may change the result, see examples. LiteralsFirstInComparisons (Priority: 3, Ruleset: Best Practices) https://docs.pmd-code.org/pmd-doc-7.9.0/pmd_rules_java_bestpractices.html#literalsfirstincomparisons

It can be confusing to have a field name with the same name as a method. While this is permitted, having information (field) and actions (method) is not clear naming. Developers versed in Smalltalk often prefer this approach as the methods denote accessor methods. AvoidFieldNameMatchingMethodName (Priority: 3, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.9.0/pmd_rules_java_errorprone.html#avoidfieldnamematchingmethodname

Code containing duplicate String literals can usually be improved by declaring the String as a constant field. AvoidDuplicateLiterals (Priority: 3, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.9.0/pmd_rules_java_errorprone.html#avoidduplicateliterals

Code containing duplicate String literals can usually be improved by declaring the String as a constant field. AvoidDuplicateLiterals (Priority: 3, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.9.0/pmd_rules_java_errorprone.html#avoidduplicateliterals

Java 5 introduced the varargs parameter declaration for methods and constructors. This syntactic sugar provides flexibility for users of these methods and constructors, allowing them to avoid having to deal with the creation of an array. Byte arrays in any method and String arrays in `public static void main(String[])` methods are ignored. UseVarargs (Priority: 4, Ruleset: Best Practices) https://docs.pmd-code.org/pmd-doc-7.9.0/pmd_rules_java_bestpractices.html#usevarargs

Avoid using hard-coded literals in conditional statements. By declaring them as static variables or private members with descriptive names maintainability is enhanced. By default, the literals "-1" and "0" are ignored. More exceptions can be defined with the property "ignoreMagicNumbers". The rule doesn't consider deeper expressions by default, but this can be enabled via the property `ignoreExpressions`. With this property set to false, if-conditions like `i == 1 + 5` are reported as well. Note that in that case, the property ignoreMagicNumbers is not taken into account, if there are multiple literals involved in such an expression. AvoidLiteralsInIfCondition (Priority: 3, Ruleset: Error Prone) https://docs.pmd-code.org/pmd-doc-7.9.0/pmd_rules_java_errorprone.html#avoidliteralsinifcondition

Reports assignments to variables that are never used before the variable is overwritten, or goes out of scope. Unused assignments are those for which 1. The variable is never read after the assignment, or 2. The assigned value is always overwritten by other assignments before the next read of the variable. The rule tracks assignements to fields of `this`, and static fields of the current class. This may cause some false positives in timing-sensitive concurrent code, which the rule cannot detect. The rule may be suppressed with the standard `@SuppressWarnings("unused")` tag. The rule subsumes {% rule "UnusedLocalVariable" %}, and {% rule "UnusedFormalParameter" %}. Those violations are filtered out by default, in case you already have enabled those rules, but may be enabled with the property `reportUnusedVariables`. Variables whose name starts with `ignored` or `unused` are filtered out, as is standard practice for exceptions. Limitations: * The rule currently cannot know which method calls throw exceptions, or which exceptions they throw. In the body of a try block, every method or constructor call is assumed to throw. This may cause false-negatives. The only other language construct that is assumed to throw is the `throw` statement, in particular, things like `assert` statements, or NullPointerExceptions on dereference are ignored. * The rule cannot resolve assignments across constructors, when they're called with the special `this(...)` syntax. This may cause false-negatives. Both of those limitations may be partly relaxed in PMD 7. UnusedAssignment (Priority: 3, Ruleset: Best Practices) https://docs.pmd-code.org/pmd-doc-7.9.0/pmd_rules_java_bestpractices.html#unusedassignment

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-7.9.0/pmd_rules_java_bestpractices.html#nonexhaustiveswitch

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-7.9.0/pmd_rules_java_performance.html#redundantfieldinitializer