checkstyle.xml

<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
    "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
    "https://checkstyle.org/dtds/configuration_1_3.dtd">

<!--
    Checkstyle configuration for java-tutorials.
    Based on Google Java Style with relaxations for a learning repository.
-->
<module name="Checker">
    <property name="charset" value="UTF-8"/>
    <property name="severity" value="warning"/>
    <property name="fileExtensions" value="java"/>

    <!-- File length -->
    <module name="FileLength">
        <property name="max" value="500"/>
    </module>

    <!-- No tabs -->
    <module name="FileTabCharacter">
        <property name="eachLine" value="true"/>
    </module>

    <!-- Trailing whitespace -->
    <module name="RegexpSingleline">
        <property name="format" value="\s+$"/>
        <property name="message" value="Line has trailing whitespace"/>
    </module>

    <!-- Line length (must be under Checker, not TreeWalker) -->
    <module name="LineLength">
        <property name="max" value="120"/>
        <property name="ignorePattern" value="^package.*|^import.*|a]* href|href|http://|https://|ftp://"/>
    </module>

    <module name="TreeWalker">
        <!-- Naming conventions -->
        <module name="ConstantName"/>
        <module name="LocalFinalVariableName"/>
        <module name="LocalVariableName"/>
        <module name="MemberName"/>
        <module name="MethodName"/>
        <module name="PackageName"/>
        <module name="ParameterName"/>
        <module name="StaticVariableName"/>
        <module name="TypeName"/>

        <!-- Imports -->
        <module name="AvoidStarImport"/>
        <module name="IllegalImport"/>
        <module name="RedundantImport"/>
        <module name="UnusedImports"/>

        <!-- Size violations -->
        <module name="MethodLength">
            <property name="max" value="60"/>
        </module>
        <module name="ParameterNumber">
            <property name="max" value="7"/>
        </module>

        <!-- Whitespace -->
        <module name="EmptyForIteratorPad"/>
        <module name="GenericWhitespace"/>
        <module name="MethodParamPad"/>
        <module name="NoWhitespaceAfter"/>
        <module name="NoWhitespaceBefore"/>
        <module name="ParenPad"/>
        <module name="TypecastParenPad"/>
        <module name="WhitespaceAfter"/>
        <module name="WhitespaceAround">
            <property name="allowEmptyConstructors" value="true"/>
            <property name="allowEmptyMethods" value="true"/>
            <property name="allowEmptyTypes" value="true"/>
            <property name="allowEmptyLoops" value="true"/>
        </module>

        <!-- Modifier checks -->
        <module name="ModifierOrder"/>
        <module name="RedundantModifier"/>

        <!-- Block checks -->
        <module name="AvoidNestedBlocks"/>
        <module name="EmptyBlock"/>
        <module name="LeftCurly"/>
        <module name="NeedBraces"/>
        <module name="RightCurly"/>

        <!-- Coding -->
        <module name="EmptyStatement"/>
        <module name="EqualsHashCode"/>
        <module name="IllegalInstantiation"/>
        <module name="InnerAssignment"/>
        <module name="MissingSwitchDefault"/>
        <module name="MultipleVariableDeclarations"/>
        <module name="SimplifyBooleanExpression"/>
        <module name="SimplifyBooleanReturn"/>

        <!-- Class design -->
        <module name="FinalClass"/>
        <module name="HideUtilityClassConstructor"/>
        <module name="InterfaceIsType"/>

        <!-- Miscellaneous -->
        <module name="ArrayTypeStyle"/>
        <module name="TodoComment">
            <property name="severity" value="info"/>
        </module>
        <module name="UpperEll"/>
    </module>
</module>