checkstyle.xml

<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
          "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
          "https://checkstyle.org/dtds/configuration_1_3.dtd">
          
<!-- 
    Configuration file for style checker
    See https://checkstyle.sourceforge.io/config.html 
  -->

<module name="Checker">
  
    <!-- BeforeExecutionFileFilters is required for sources that are based on java9 -->
    <module name="BeforeExecutionExclusionFileFilter">
        <property name="fileNamePattern" value="module\-info\.java$"/>
    </module>
    
    <!-- Filters -->

    <!-- Allow long test files -->
    <module name="SuppressionSingleFilter">
        <property name="files" value="test.*"/>
        <property name="checks" value="FileLength"/>
    </module>
    <!-- Allow test packages to not be documented -->
    <module name="SuppressionSingleFilter">
        <property name="files" value="test.*"/>
        <property name="checks" value="JavadocPackage"/>
    </module>
    <!-- Test classes do not need constructors -->
    <module name="SuppressionSingleFilter">
        <property name="files" value="test.*"/>
        <property name="checks" value="MissingCtor"/>
    </module>
    <module name="SuppressionSingleFilter">
        <property name="files" value="test.*"/>
        <property name="checks" value="HideUtilityClassConstructor"/>
    </module>
    <!-- Allow unrestricted string literals in test classes -->
    <module name="SuppressionSingleFilter">
        <property name="files" value="test.*"/>
        <property name="checks" value="MultipleStringLiterals"/>
    </module>
    <!-- Allow magic numbers in test classes -->
    <module name="SuppressionSingleFilter">
        <property name="files" value="test.*"/>
        <property name="checks" value="MagicNumber"/>
    </module>
    <!-- Method comments aren't necessary in test classes -->
    <module name="SuppressionSingleFilter">
        <property name="files" value="test.*"/>
        <property name="checks" value="JavadocMethod"/>
    </module>
    <!-- required till https://bugs.openjdk.java.net/browse/JDK-8160601 -->
    <module name="SuppressionSingleFilter">
        <property name="checks" value="MissingDeprecatedCheck"/>
        <property name="files" value="package-info\.java"/>
    </module>
    <!-- @SuppressWarnings support -->
    <module name="SuppressWarningsFilter"/>

    <!-- <p> tag checking kind of broken with some tags -->
    <module name="SuppressWithPlainTextCommentFilter">
        <property name="offCommentFormat" value="BEGIN BUGGED PARAGRAPH"/>
        <property name="onCommentFormat" value="END BUGGED PARAGRAPH"/>
        <property name="checkFormat" value="JavadocParagraph"/>
    </module>
    
    <!-- File structure checks -->
   
    <!-- Log very long files (>2k lines) -->
    <module name="FileLength">
        <property name="severity" value="info"/>
    </module>
    
     <!-- Files should not use tabs and end with a newline -->
    <module name="FileTabCharacter"/>
    <module name="NewlineAtEndOfFile"/>
    
    <!-- Lines should be no longer than 100 characters -->
    <module name="LineLength">
        <property name="max" value="100"/>
    </module>
    <module name="SuppressWithPlainTextCommentFilter">
        <property name="offCommentFormat" value="BEGIN LONG LINES"/>
        <property name="onCommentFormat" value="END LONG LINES"/>
        <property name="checkFormat" value="LineLength"/>
    </module>
    
    <!-- Package checks -->
    
    <!-- All packages should have a javadoc header -->
    <module name="JavadocPackage"/>
    
    <!-- Containers -->
    <module name="TreeWalker">
    
        <!-- Detect @SuppressWarnings for SuppressWarningsFilter -->
        <module name="SuppressWarningsHolder"/>
        
    </module>
    
    <!-- Annotation checks -->
    <module name="TreeWalker">
    
        <!-- Annotations should be between the javadoc header and the element -->
        <module name="AnnotationLocation">
            <property name="allowSamelineMultipleAnnotations" value="true"/>
        </module>
        <!-- 
            Keep annotation as compact as possible (e.g. no array when it's a single 
            value, etc)
          -->
        <module name="AnnotationUseStyle"/>
        
    </module>
    
    <!-- Array/Collection checks -->
    <module name="TreeWalker">
        
        <!-- Add trailing comma to array initializers (except for inline initializers) -->
        <module name="ArrayTrailingComma">
            <property name="severity" value="warning"/>
        </module>
        <!-- Don't use double-brace initialization -->
        <module name="AvoidDoubleBraceInitialization"/>
        <!-- Use Java-style arrays (e.g. String[] arr) -->
        <module name="ArrayTypeStyle"/>

    </module>
    
    <!-- Javadoc checks -->
    <module name="TreeWalker">
        
        <!-- Order of tags in javadoc headers -->
        <module name="AtclauseOrder">
            <property name="tagOrder"
                value="@param, @return, @throws, @exception, @see, 
                       @serial, @serialField, @serialData, 
                       @author, @version, @since, 
                       @apiNote, @implSpec, @implNote, @deprecated"/>
        </module>
        <!-- Javadoc headers must be in valid positions -->
        <module name="InvalidJavadocPosition"/>
        <!-- Block tags must be at the start of a line, except inline tags -->
        <module name="JavadocBlockTagLocation"/>
        <!-- Javadoc content must start at the second line -->
        <module name="JavadocContentLocationCheck"/>
        <!-- Method javadoc must document all parameters, return value, and thrown exceptions -->
        <module name="JavadocMethod">
            <property name="validateThrows" value="true"/>
        </module>
        <!-- Must have a space after the leading asterisk -->
        <module name="JavadocMissingWhitespaceAfterAsterisk"/>
        <!-- 
            There must be a blank line between paragraphs, and all paragraphs other 
            than the first must start with <p>
          -->
        <module name="JavadocParagraph"/>
        <!-- Javadoc comment must be well-formed and may not be empty -->
        <!-- This module refuses to be suppressed so it was turned off -->
        <!-- <module name="JavadocStyle">
            <property name="checkEmptyJavadoc" value="true"/>
        </module> -->
        <!-- <module name="SummaryJavadocCheck"/> -->
        <!-- Javadoc tag continuation must be indented by at least 4 spaces -->
        <module name="JavadocTagContinuationIndentation"/>
        <!-- Type headers must document generic type parameters, author, version, and since -->
        <module name="JavadocType">
            <!-- <property name="authorFormat" value="\S(.*\S)?"/> -->
            <property name="versionFormat" value="[1-9]\d*\.\d+"/> <!-- At least 1.0 -->
            <!-- Unfortunately we cannot add implNote, implSpec, apiNote and apiSpec to checkstyle -->
            <property name="allowUnknownTags" value="true"/>
        </module>
        <!-- @since may have a placeholder instead of a version (for pending releases) -->
        <module name="WriteTag">
            <property name="tag" value="@since"/>
            <property name="tagFormat" value="(\d+\.\d+)|(TODO:VERSION)"/>
            <property name="tagSeverity" value="ignore"/>
        </module>
        <!-- Variables other than "serialVersionUID" or "log" must be documented -->
        <module name="JavadocVariable">
            <property name="ignoreNamePattern" value="log"/>
        </module>
        <!-- @Deprecated annotation and @deprecated javadoc tag always go together -->
        <module name="MissingDeprecated"/>
        <!-- All non-@Override methods must have javadoc comments -->
        <module name="MissingJavadocMethod">
            <property name="scope" value="private"/>
        </module>
        <!-- All types and packages must have javadoc comments -->
        <module name="MissingJavadocPackage"/>
        <module name="MissingJavadocType">
            <property name="scope" value="private"/>
        </module>
        <!-- Non-inline tags must have a description -->
        <module name="NonEmptyAtclauseDescription"/>
        <!-- Single-line javadoc cannot have non-inline tags -->
        <module name="SingleLineJavadoc"/>
        <!-- There must be an empty line before the first javadoc tag -->
        <module name="RequireEmptyLineBeforeBlockTagGroup"/>

    </module>
    
    <!-- String checks -->
    <module name="TreeWalker">
        
        <!-- 
            Don't use escaped Unicode characters (use the actual character instead, unless:
            - It is a control character
            - It is a non-printable escape character
            - All characters in the string are escaped 
          -->
        <module name="AvoidEscapedUnicodeCharacters">
            <property name="severity" value="warning"/>
            <property name="allowEscapesForControlCharacters" value="true"/>
            <property name="allowNonPrintableEscapes" value="true"/>
            <property name="allowIfAllCharactersEscaped" value="true"/>
        </module>
        <!-- String literals should be on the left side of equals() -->
        <module name="EqualsAvoidNull"/>
        <!-- Avoid multiple copies of string literal in file -->
        <module name="MultipleStringLiterals">
            <property name="severity" value="warning"/>
        </module>
        <!-- Don't use == or != with String literals -->
        <module name="StringLiteralEquality"/>

    </module>
    
    <!-- Redundancy checks -->
    <module name="TreeWalker">
        
        <!-- Avoid nested blocks (other than switch cases) -->
        <module name="AvoidNestedBlocks">
            <property name="severity" value="warning"/>
            <property name="allowInSwitchCase" value="true"/>
        </module>
        <!-- Avoid explicitly calling super() in constructor -->
        <module name="AvoidNoArgumentSuperConstructorCall">
            <property name="severity" value="warning"/>
        </module>
        <!-- Avoid empty statements -->
        <module name="EmptyStatement"/>
        <!-- Log class/object members explicitly initialized to their default value -->
        <module name="ExplicitInitialization">
            <property name="severity" value="info"/>
        </module>
        <!-- Avoid explicitly specifying implicit modifiers -->
        <module name="RedundantModifier"/>
        <!-- Flag boolean expressions that can be simplified -->
        <module name="SimplifyBooleanExpression"/>
        <module name="SimplifyBooleanReturn"/>
        <!-- Avoid redundant parenthesis in expressions -->
        <module name="UnnecessaryParentheses">
            <property name="severity" value="info"/>
        </module>
        <!-- Avoid redundant semicolon in constant-only enums -->
        <module name="UnnecessarySemicolonInEnumeration"/>
        <!-- Avoid redundant semicolon in last resource -->
        <module name="UnnecessarySemicolonInTryWithResources"/>
        <!-- Avoid redundant semicolon after type declaration -->
        <module name="UnnecessarySemicolonAfterOuterTypeDeclaration"/>
        <!-- Avoid redundant semicolon after member declaration in type -->
        <module name="UnnecessarySemicolonAfterTypeMemberDeclaration"/>

    </module>
    
    <!-- Import checks -->
    <module name="TreeWalker">
        
        <!-- Avoid star imports (other than JUnit and JAssert assertions) -->
        <module name="AvoidStarImport">
            <property name="excludes" value="org.junit.jupiter.api.Assertions,org.assertj.core.api.Assertions"/>
        </module>
        <!-- Avoid static imports (other than JUnit and JAssert assertions) -->
        <module name="AvoidStaticImport">
            <property name="excludes" value="org.junit.jupiter.api.Assertions.*,org.assertj.core.api.Assertions.*"/>
        </module>
        <!-- 
            Must follow Eclipse import order:
            1. static imports
            2. java and javax packages
            3. org and com packages
            4. all other imports
            Imports should be sorted within groups, and groups should  be separated
            from each other by one blank line (but should not be separated internally)
          -->
        <module name="ImportOrder">
            <property name="groups" value="/^java\./,javax,com,org"/>
            <property name="ordered" value="true"/>
            <property name="separated" value="true"/>
            <property name="option" value="top"/>
            <property name="sortStaticImportsAlphabetically" value="true"/>
        </module>
        <!-- Avoid redundant imports -->
        <module name="RedundantImport"/>
        <!-- Avoid unused imports -->
        <module name="UnusedImports">
            <property name="severity" value="warning"/>
        </module>

    </module>
    
    <!-- Complexity/length checks -->
    <module name="TreeWalker">
        
        <!-- Log very complex boolean expressions (>5 operators) -->
        <module name="BooleanExpressionComplexity">
            <property name="severity" value="info"/>
            <property name="max" value="5"/>
        </module>
        <!-- 
            Avoid high cyclomatic complexity (>20)
            (https://checkstyle.sourceforge.io/config_metrics.html#CyclomaticComplexity)
          -->
        <module name="CyclomaticComplexity">
            <property name="severity" value="warning"/>
            <property name="max" value="20"/>
        </module>
        <!-- Log constructors/methods with too many executable statements (>50) -->
        <module name="ExecutableStatementCount">
            <property name="severity" value="info"/>
            <property name="max" value="50"/>
        </module>
        <!-- Avoid excessively long methods (>150 lines) -->
        <module name="MethodLength">
            <property name="severity" value="warning"/>
        </module>
        <!--
            Log methods with a high NPATH complexity (>500) 
            (https://checkstyle.sourceforge.io/config_metrics.html#NPathComplexity)
          -->
        <module name="NPathComplexity">
            <property name="severity" value="info"/>
            <property name="max" value="500"/>
        </module>
        <!-- Log non-@Override methods with many parameters (>10) -->
        <module name="ParameterNumber">
            <property name="severity" value="info"/>
            <property name="ignoreOverriddenMethods" value="true"/>
            <property name="max" value="10"/>
        </module>

    </module>
    
    <!-- Naming checks -->
    <module name="TreeWalker">
        
        <!-- 
            Parameter of catch clause should be named as one of:
            - two lower case letters + one or more upper or lower case letter
            - "e"
            - "ex"
            - "t"
          -->
        <module name="CatchParameterName"/>
        <!-- Class type parameters should be 1-3 upper case letters (optionally with numbers at the end), or "SELF" -->
        <module name="ClassTypeParameterName">
            <property name="format" value="^[A-Z]{1,3}[0-9]*$|^SELF$"/>
        </module>
        <module name="InterfaceTypeParameterName">
            <property name="format" value="^[A-Z]{1,3}[0-9]*$|^SELF$"/>
        </module>
        <module name="RecordTypeParameterName">
            <property name="format" value="^[A-Z]{1,3}[0-9]*$|^SELF$"/>
        </module>
        <!-- 
            Variable names must start with a lower case letter, and only 
            contain letters and numbers 
          -->
        <module name="LocalFinalVariableName"/>
        <module name="LocalVariableName"/>
        <module name="MemberName"/>
        <module name="ParameterName"/>
        <module name="PatternVariableName"/>
        <module name="StaticVariableName"/>
        <module name="RecordComponentName"/>
        <!-- 
            Method names must start with a lower case letter, and only 
            contain letters and numbers .
            Methods may not have the same name as the class they are in.
          -->
        <module name="MethodName"/>
        <!-- Method type parameters should be one or two upper case letters -->
        <module name="MethodTypeParameterName">
            <property name="format" value="^[A-Z]{1,2}$"/>
        </module>
        <!-- 
            Package names should start with a lower case letter and only contain lower case
            letters and numbers. The root package name may not contain numbers.
          -->
        <module name="PackageName">
            <property name="format" value="^[a-z]+(\.[a-z][a-z0-9_]*)*$"/>
        </module>
        <!-- 
            Type names must start with an upper case letter, and only 
            contain letters and numbers 
          -->
        <module name="TypeName"/>

    </module>
    
    <!-- Whitespace checks -->
    <module name="TreeWalker">
        
        <!-- Comments should be indented at the same level as surrounding code -->
        <module name="CommentsIndentation"/>
        <!-- Add single space of padding for empty for initializer or iterator -->
        <module name="EmptyForInitializerPad">
            <property name="option" value="space"/>
        </module>
        <module name="EmptyForIteratorPad">
            <property name="option" value="space"/>
        </module>
        <!-- 
            Must have empty line separators after header, package, all import 
            declarations, fields, constructors, methods, nested classes, static 
            initializers and instance initializers.
            May omit separator between fields.
            May not have multiple blank lines between elements.
          -->
        <module name="EmptyLineSeparator">
            <property name="allowNoEmptyLineBetweenFields" value="true"/>
            <property name="allowMultipleEmptyLines" value="false"/>
            <property name="allowMultipleEmptyLinesInsideClassMembers" value="false"/>
        </module>
        <!-- 
            Whitespace around generic tokens should follow typical convention
            (https://checkstyle.sourceforge.io/config_whitespace.html#GenericWhitespace)
          -->
        <module name="GenericWhitespace"/>
        <!-- 
            4 spaces per indent level
            - Closing braces on the same level as opening statement
            - Indent case labels by one level
            - Indent code in case by one level from label
            - Indent throws clause by two levels (if on separate line)
            - Indent array initializer by two levels (if on separate line)
            This is the minimum, indent may be larger if necessary
          -->
        <module name="Indentation">
            <property name="throwsIndent" value="8"/>
            <property name="arrayInitIndent" value="8"/>
            <property name="lineWrappingIndentation" value="8"/>
        </module>
        <!-- Left curly brace must be at the end of the line -->
        <module name="LeftCurly">
            <property name="ignoreEnums" value="false"/>
        </module>
        <!-- Don't put a space between method name and parenthesis -->
        <module name="MethodParamPad"/>
        <!-- Import and package statements should not wrap -->
        <module name="NoLineWrap"/>
        <!-- 
            No space after:
            - @ (annotations)
            - pre-token unary operators (pre-increment, pre-decrement, ~, !)
            - .
            - [
          -->
        <module name="NoWhitespaceAfter">
            <property name="tokens"
                value="AT, INC, DEC, UNARY_MINUS, UNARY_PLUS, BNOT, LNOT,
                       DOT, ARRAY_DECLARATOR, INDEX_OP"/>
            <property name="allowLineBreaks" value="false"/>
        </module>
        <!-- 
            No space before:
            - ,
            - ;
            - post-token unary operators (post-increment, post-decrement)
            - ...
            - : (labels)
          -->
        <module name="NoWhitespaceBefore"/>
        <module name="NoWhitespaceBeforeCaseDefaultColon"/>
        <!-- When wrapping an expression, operator goes into new line -->
        <module name="OperatorWrap"/>
        <!-- Pad parenthesis with spaces (after left and before right parenthesis) -->
        <module name="ParenPad">
            <property name="option" value="space"/>
        </module>
        <!--
            Right curly brace must be alone in line, except when followed by else/catch/etc in
            block (still must be at the start of the line) or part of a single-line expression
          -->
        <module name="RightCurly"/>
        <!-- When wrapping, comma must be at the end of the current line -->
        <module name="SeparatorWrap">
            <property name="tokens" value="COMMA"/>
            <property name="option" value="eol"/>
        </module>
        <!-- When wrapping, period must be at the start of the next line -->
        <module name="SeparatorWrap">
            <property name="tokens" value="DOT"/>
            <property name="option" value="nl"/>
        </module>
        <!-- Avoid multiple spaces -->
        <module name="SingleSpaceSeparator"/>
        <!-- Pad typecast parenthesis with spaces (after left and before right parenthesis) -->
        <module name="TypecastParenPad">
            <property name="option" value="space"/>
        </module>
        <!--
            Always have a space after:
            - ,
            - ; (except for empty for)
            - Type casts
            - Control flow statements (if, else, while, do) 
          -->
        <module name="WhitespaceAfter"/>
        <!-- 
            Always have a space around:
            - Non-unary operators
            - Keywords (if, catch, synchronized, etc)
            - Curly braces (no space required within an empty block, that is "{}")
            - Enhanced-for colon
          -->
        <module name="WhitespaceAround">
            <property name="allowEmptyConstructors" value="true"/>
            <property name="allowEmptyMethods" value="true"/>
            <property name="allowEmptyTypes" value="true"/>
            <property name="allowEmptyLoops" value="true"/>
            <property name="allowEmptyLambdas" value="true"/>
            <property name="allowEmptyCatches" value="true"/>
            <property name="ignoreEnhancedForColon" value="false"/>
        </module>

    </module>
    
    <!-- Override checks -->
    <module name="TreeWalker">
        
        <!-- 
            If class defines equals() with a parameter other than Object,
            should also override equals(Object) 
          -->
        <module name="CovariantEquals"/>
        <!-- A class that overrides equals() should also override hashCode() and vice versa -->
        <module name="EqualsHashCode"/>
        <!-- If overriding clone(), must call super.clone() -->
        <module name="SuperClone"/>
        <!-- If overriding finalize(), must call super.finalize() -->
        <module name="SuperFinalize"/>

    </module>
    
    <!-- Ordering checks -->
    <module name="TreeWalker">
        
        <!--
            Declare class members in the order:
            1. Static variables
            2. Instance variables
            3. Constructors
            4. Methods
            Within each type, also keep this order:
            1. public
            2. protected
            3. package/default
            4. private 
          -->
        <module name="DeclarationOrder">
            <property name="severity" value="warning"/>
        </module>
        <!-- Default case in switch should be the last one -->
        <module name="DefaultComesLast">
            <property name="severity" value="warning"/>
        </module>
        <!-- Declare inner types at the end of class/interface (after methods) -->
        <module name="InnerTypeLast">
            <property name="severity" value="warning"/>
        </module>
        <!--
            Modifiers must follow this order:
            1.  public
            2.  protected
            3.  private
            4.  abstract
            5.  default
            6.  static
            7.  final
            8.  transient
            9.  volatile
            10. synchronized
            11. native
            12. strictfp
          -->
        <module name="ModifierOrder"/>
        <!-- Overloaded methods must be grouped together -->
        <module name="OverloadMethodsDeclarationOrder">
            <property name="severity" value="warning"/>
        </module>

    </module>
    
    <!-- Missing code/sanity checks -->
    <module name="TreeWalker">
        
        <!-- Avoid empty block in switch case (other than fall-through) -->
        <module name="EmptyBlock"/>
        <!-- 
            Avoid empty catch block, unless it contains one of the following 
            comments in the first line:
            - // Expected
            - // expected
            - // Ignore
            - // ignore
         -->
        <module name="EmptyCatchBlock">
            <property name="commentFormat" value="^\s*([eE]xpected|[iI]gnore).*"/>
        </module>
        <!--
            Flag cases that fall through in a switch, unless one of these comments
            (by itself) is the last non-empty line in the case:
            - // fallthru
            - // fall thru
            - // fall-thru
            - // fallthrough
            - // fall through
            - // fall-through
            - // fallsthrough
            - // falls through
            - // falls-through
          -->
        <module name="FallThrough"/>
        <!-- Classes with only private constructors should be final -->
        <module name="FinalClass"/>
        <!-- 
            Log local variables or parameters (including enchanced-for variable) that 
            never change but are not final
          -->
        <module name="FinalLocalVariable">
            <property name="severity" value="info"/>
            <property name="tokens" value="VARIABLE_DEF,PARAMETER_DEF"/>
            <property name="validateEnhancedForLoopVariable" value="true"/>
        </module>
        <!-- 
            Local variable or parameter should not hide class field, unless 
            it's a parameter of a setter or constructor
          -->
        <module name="HiddenField">
            <property name="ignoreConstructorParameter" value="true"/>
            <property name="ignoreSetter" value="true"/>
            <property name="setterCanReturnItsClass" value="true"/>
        </module>
        <!-- Classes with only static members should not have a public constructor -->
        <module name="HideUtilityClassConstructor"/>
        <!-- Non-abstract classes should define a constructor (not use the default one -->
        <module name="MissingCtor">
            <property name="severity" value="warning"/>
        </module>
        <!-- A method using @inheritDoc must have @Override -->
        <module name="MissingOverride"/>
        <!-- Must have default case in switch -->
        <module name="MissingSwitchDefault"/>
        <!-- Avoid modifying loop variable in for (except enhanced-for) -->
        <module name="ModifiedControlVariable">
            <property name="skipEnhancedForLoopVariable" value="true"/>
        </module>
        <!-- Exception classes must be immutable (only final fields) -->
        <module name="MutableException"/>
        <!-- 
            Code blocks must have braces. Loops with empty bodies may
            omit the braces and just use a semicolon.
          -->
        <module name="NeedBraces">
            <property name="allowEmptyLoopBody" value="true"/>
        </module>
        <!-- Flag files with no code -->
        <module name="NoCodeInFile"/>
        <!-- A type should be in a file of the same name -->
        <module name="OuterTypeFilename"/>
        <!-- Classes should declare a package, that should match the directory structure -->
        <module name="PackageDeclaration"/>
        <!-- Flag TODO comments -->
        <module name="TodoComment">
            <property name="severity" value="info"/>
            <property name="format" value="(TODO:(?!VERSION))|(FIXME)"/>
        </module>
        <!-- Log version placeholders -->
        <module name="TodoComment">
            <property name="severity" value="info"/>
            <property name="format" value="TODO:VERSION"/>
        </module>
        <!-- Flag classes with a main() method -->
        <module name="UncommentedMain">
            <property name="severity" value="warning"/>
            <property name="excludedClasses" value="\.TestBot$"/> <!-- Allow test bot -->
        </module>
        <!-- Use upper case L for long int literals -->
        <module name="UpperEll"/>
        <!-- Avoid public non-final variables -->
        <module name="VisibilityModifier">
            <property name="packageAllowed" value="true"/>
            <property name="protectedAllowed" value="true"/>
            <property name="allowPublicFinalFields" value="true"/>
        </module>

    </module>
    
    <!-- Illegal code check -->
    <module name="TreeWalker">
        
        <!-- Never catch Error, Exception, RuntimeException, or Throwable -->
        <module name="IllegalCatch"/>
        <!-- Never use language keywords for identifiers -->
        <module name="IllegalIdentifierName"/>
        <!-- Don't import sun.* (internal) packages -->
        <module name="IllegalImport"/>
        <!-- Don't declare a method throws Error, RuntimeException, or Throwable -->
        <module name="IllegalThrows">
            <property name="ignoreOverriddenMethods" value="false"/>
        </module>
        <!-- Log usage of labels or native methods -->
        <module name="IllegalToken">
            <property name="severity" value="info"/>
            <property name="tokens" value="LABELED_STAT,LITERAL_NATIVE"/>
        </module>
        <!-- Don't use concrete types for variable type, use the interface -->
        <module name="IllegalType">
            <property name="illegalClassNames"
                value="HashMap, java.util.HashMap, 
                       HashSet, java.util.HashSet, 
                       LinkedHashMap, java.util.LinkedHashMap, 
                       LinkedHashSet, java.util.LinkedHashSet, 
                       TreeMap, java.util.TreeMap, 
                       TreeSet, java.util.TreeSet,
                       GregorianCalendar, java.util.GregorianCalendar,
                       Hashtable, java.util.Hashtable,
                       ArrayList, java.util.ArrayList,
                       LinkedList, java.util.LinkedList,
                       Vector, java.util.Vector"/>
        </module>
        <!-- Don't do assignments as subexpressions -->
        <module name="InnerAssignment"/>
        <!-- Don't use magic numbers outside of annotations -->
        <module name="MagicNumber">
            <property name="severity" value="warning"/>
            <property name="ignoreAnnotation" value="true"/>
        </module>
        <!-- Don't declare multiple variables in the same statement or line -->
        <module name="MultipleVariableDeclarations"/>
        <!-- Don't override clone() or finalize() -->
        <module name="NoClone"/>
        <module name="NoFinalizer"/>
        <!--
            Only do one statement per line. In try-with-resources,
            a variable reference does not count as a statement. 
          -->
        <module name="OneStatementPerLine">
            <property name="treatTryResourcesAsStatement" value="true"/>
        </module>
        <!-- Only have one outer type per file -->
        <module name="OneTopLevelClass"/>
        <module name="OuterTypeNumber"/>

    </module>
</module>