Programmierprojekt/config/checkstyle/checkstyle.xml

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

<module name="Checker">
    <!-- Fail build if checkstyle finds violations -->
    <!-- https://checkstyle.sourceforge.io/config.html#Properties_1 -->
    <property name="severity" value="error"/>

    <!-- Only check java files -->
    <!-- https://checkstyle.sourceforge.io/config.html#Properties_1 -->
    <property name="fileExtensions" value="java"/>

    <module name="SuppressionFilter">
        <property name="file" value="${suppressionFile}"/>
    </module>

    <!-- Only allow spaces -->
    <!-- https://checkstyle.sourceforge.io/checks/whitespace/filetabcharacter.html -->
    <module name="FileTabCharacter"/>

    <!-- Maximale Zeilenlänge (AOSP enforces 100 lines, the Google Java Style Guide 80)-->
    <!-- https://checkstyle.sourceforge.io/checks/sizes/linelength.html -->
    <module name="LineLength">
        <property name="max" value="100"/>
    </module>

    <module name="TreeWalker">
        <!-- Allows for emptylines BETWEEN methods and classes but DISALLOWS newlines after an opening bracket -->
        <!-- https://checkstyle.sourceforge.io/checks/whitespace/emptylineseparator.html -->
        <module name="EmptyLineSeparator">
            <property name="allowNoEmptyLineBetweenFields" value="true"/>
            <property name="tokens" value="
                METHOD_DEF,
                CTOR_DEF,
                STATIC_INIT,
                INSTANCE_INIT,
                CLASS_DEF,
                INTERFACE_DEF,
                ENUM_DEF
            "/>
        </module>

        <!-- No wildcard imports (import x.*) -->
        <!-- https://checkstyle.sourceforge.io/checks/imports/avoidstarimport.html -->
        <module name="AvoidStarImport"/>

        <!-- No unused imports -->
        <!-- https://checkstyle.sourceforge.io/checks/imports/unusedimports.html -->
        <module name="UnusedImports"/>

        <!-- No unordered / ungrouped imports -->
        <!-- https://checkstyle.sourceforge.io/checks/imports/importorder.html -->
        <module name="ImportOrder">
            <property name="option" value="top"/>
            <property name="groups" value="/^import static\..+/,*"/>
            <property name="separated" value="true"/>
            <property name="separatedStaticGroups" value="true"/>
            <property name="sortStaticImportsAlphabetically" value="true"/>
        </module>

        <!-- Classes, enums, records, ... as PascalCase -->
        <!-- https://checkstyle.sourceforge.io/checks/naming/typename.html -->
        <module name="TypeName"/>

        <!-- Method names as camelCase -->
        <!-- https://checkstyle.sourceforge.io/checks/naming/methodname.html -->
        <module name="MethodName"/>

        <!-- Parameter names as camelCase -->
        <!-- https://checkstyle.sourceforge.io/checks/naming/parametername.html -->
        <module name="ParameterName"/>

        <!-- Lokal variables as camelCase -->
        <!-- https://checkstyle.sourceforge.io/checks/naming/localvariablename.html -->
        <module name="LocalVariableName"/>

        <!-- Constants as UPPER_SNAKE_CASE -->
        <!-- https://checkstyle.sourceforge.io/checks/naming/constantname.html -->
        <module name="ConstantName"/>

        <!-- Field names as camelCase -->
        <!-- https://checkstyle.sourceforge.io/checks/naming/membername.html -->
        <module name="MemberName">
            <property name="format" value="^[a-z][a-zA-Z0-9]*$"/>
        </module>

        <!-- Restrict length of method name -->
        <!-- https://checkstyle.sourceforge.io/checks/sizes/methodlength.html -->
        <module name="MethodLength">
            <property name="max" value="60"/>
            <property name="countEmpty" value="false"/>
        </module>

        <!-- Restrict number of parameters -->
        <!-- https://checkstyle.sourceforge.io/checks/sizes/parameternumber.html -->
        <module name="ParameterNumber">
            <property name="max" value="5"/>
        </module>

        <!-- Modifier-Reihenfolge: public static final ... -->
        <!-- https://checkstyle.sourceforge.io/checks/modifier/modifierorder.html -->
        <module name="ModifierOrder"/>

        <!-- Require braces arround code block (no single instruction after if/else/while/...)-->
        <!-- https://checkstyle.sourceforge.io/checks/blocks/needbraces.html -->
        <module name="NeedBraces"/>

        <!-- Require the left curly braces at the same line -->
        <!-- https://checkstyle.sourceforge.io/checks/blocks/leftcurly.html -->
        <module name="LeftCurly"/>

        <!-- Require right curly braces at the same line as following instructions -->
        <!-- https://checkstyle.sourceforge.io/checks/blocks/rightcurly.html -->
        <module name="RightCurly"/>

        <!-- Disallow empty code blocks -->
        <!-- https://checkstyle.sourceforge.io/checks/blocks/emptyblock.html -->
        <module name="EmptyBlock">
            <property name="option" value="text"/>
        </module>

        <!-- Disallow empty code blocks after catch -->
        <!-- https://checkstyle.sourceforge.io/checks/blocks/emptycatchblock.html -->
        <module name="EmptyCatchBlock">
            <property name="exceptionVariableName" value="expected|ignored"/>
        </module>

        <!-- Require string literals to be compared with .equals and not == -->
        <!-- https://checkstyle.sourceforge.io/checks/coding/stringliteralequality.html -->
        <module name="StringLiteralEquality"/>

        <!-- Disallow standalone numbers in code -->
        <!-- https://checkstyle.sourceforge.io/checks/coding/magicnumber.html -->
        <module name="MagicNumber">
            <property name="ignoreNumbers" value="-1, 0, 1, 2"/>
            <property name="ignoreAnnotation" value="true"/>
        </module>

        <!-- Disallow nested code blocks dangling in code -->
        <!-- https://checkstyle.sourceforge.io/checks/blocks/avoidnestedblocks.html -->
        <module name="AvoidNestedBlocks"/>

        <!-- Disallow System.out.println -->
        <!-- https://checkstyle.sourceforge.io/checks/regexp/regexp.html -->
        <module name="Regexp">
            <property name="id" value="SystemOutErr"/>
            <property name="format" value="System\.(out|err)\.print"/>
            <property name="illegalPattern" value="true"/>
            <property name="message" value="No `System.out.print(err)` allowed — use a logger."/>
        </module>

        <!-- Disallow whitespace before semicolon or bracket -->
        <!-- https://checkstyle.sourceforge.io/checks/whitespace/nowhitespacebefore.html -->
        <module name="NoWhitespaceBefore"/>

        <!-- Disallow whitespace after code -->
        <!-- https://checkstyle.sourceforge.io/checks/whitespace/whitespaceafter.html -->
        <module name="WhitespaceAfter"/>

        <!-- No trailing whitespace at line ending -->
        <!-- https://checkstyle.sourceforge.io/checks/regexp/regexp.html -->
        <module name="Regexp">
            <property name="format" value=" +$"/>
            <property name="illegalPattern" value="true"/>
            <property name="message" value="No trailing whitespace."/>
        </module>
    </module>
</module>