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 that checks the sun coding conventions from:

    - the Java Language Specification at
      https://docs.oracle.com/javase/specs/jls/se11/html/index.html

    - the Sun Code Conventions at https://www.oracle.com/java/technologies/javase/codeconventions-contents.html

    - the Javadoc guidelines at
      https://www.oracle.com/technical-resources/articles/java/javadoc-tool.html

    - the JDK Api documentation https://docs.oracle.com/en/java/javase/11/

    - some best practices

  Checkstyle is very configurable. Be sure to read the documentation at
  https://checkstyle.org (or in your downloaded distribution).

  Most Checks are configurable, be sure to consult the documentation.

  To completely disable a check, just comment it out or delete it from the file.
  To suppress certain violations please review suppression filters.

  Finally, it is worth reading the documentation.

-->

<module name="Checker">
    <!--
        If you set the basedir property below, then all reported file
        names will be relative to the specified directory. See
        https://checkstyle.org/config.html#Checker

        <property name="basedir" value="${basedir}"/>
    -->
    <property name="severity" value="error"/>

    <property name="fileExtensions" value="java, properties, xml"/>

    <!-- Excludes all 'module-info.java' files              -->
    <!-- See https://checkstyle.org/config_filefilters.html -->
    <module name="BeforeExecutionExclusionFileFilter">
        <property name="fileNamePattern" value="module\-info\.java$"/>
    </module>

    <!-- https://checkstyle.org/config_filters.html#SuppressionFilter -->
    <module name="SuppressionFilter">
        <property name="file" value="${org.checkstyle.sun.suppressionfilter.config}"
                  default="checkstyle-suppressions.xml"/>
        <property name="optional" value="true"/>
    </module>

    <!-- Checks that a package-info.java file exists for each package.     -->
    <!-- See https://checkstyle.org/config_javadoc.html#JavadocPackage -->
    <module name="JavadocPackage"/>

    <!-- Checks whether files end with a new line.                        -->
    <!-- See https://checkstyle.org/config_misc.html#NewlineAtEndOfFile -->
    <module name="NewlineAtEndOfFile"/>

    <!-- Checks that property files contain the same keys.         -->
    <!-- See https://checkstyle.org/config_misc.html#Translation -->
    <module name="Translation"/>

    <!-- Checks for Size Violations.                    -->
    <!-- See https://checkstyle.org/config_sizes.html -->
    <module name="FileLength"/>
    <module name="LineLength">
        <property name="fileExtensions" value="java, groovy"/>
        <property name="max" value="130"/>
    </module>

    <!-- Checks for whitespace                               -->
    <!-- See https://checkstyle.org/config_whitespace.html -->
    <module name="FileTabCharacter"/>

    <!-- Miscellaneous other checks.                   -->
    <!-- See https://checkstyle.org/config_misc.html -->
    <module name="RegexpSingleline">
        <property name="format" value="\s+$"/>
        <property name="minimum" value="0"/>
        <property name="maximum" value="0"/>
        <property name="message" value="Line has trailing spaces."/>
    </module>

    <!-- Checks for Headers                                -->
    <!-- See https://checkstyle.org/config_header.html   -->
    <!-- <module name="Header"> -->
    <!--   <property name="headerFile" value="${checkstyle.header.file}"/> -->
    <!--   <property name="fileExtensions" value="java"/> -->
    <!-- </module> -->

    <module name="TreeWalker">

        <!-- Checks for Javadoc comments.                     -->
        <!-- See https://checkstyle.org/config_javadoc.html -->
        <module name="InvalidJavadocPosition"/>
        <module name="JavadocMethod"/>
        <module name="JavadocType"/>
        <module name="JavadocVariable"/>
        <module name="JavadocStyle"/>
        <module name="MissingJavadocMethod"/>

        <!-- Checks for Naming Conventions.                  -->
        <!-- See https://checkstyle.org/config_naming.html -->
        <module name="ConstantName"/>
        <module name="LocalFinalVariableName"/>
        <module name="LocalVariableName"/>
        <module name="MemberName"/>
        <module name="MethodName">
            <property name="applyToProtected" value="false"/>
        </module>
        <module name="MethodName">
            <property name="format" value="^[_a-z][a-zA-Z0-9]*$"/>
            <property name="applyToProtected" value="true"/>
        </module>
        <module name="PackageName"/>
        <module name="ParameterName"/>
        <module name="StaticVariableName"/>
        <module name="TypeName"/>

        <!-- Checks for imports                              -->
        <!-- See https://checkstyle.org/config_imports.html -->
        <module name="AvoidStarImport"/>
        <module name="IllegalImport"/> <!-- defaults to sun.* packages -->
        <module name="RedundantImport"/>
        <module name="UnusedImports">
            <property name="processJavadoc" value="false"/>
        </module>

        <!-- Checks for Size Violations.                    -->
        <!-- See https://checkstyle.org/config_sizes.html -->
        <module name="MethodLength"/>
        <module name="ParameterNumber"/>

        <!-- Checks for whitespace                               -->
        <!-- See https://checkstyle.org/config_whitespace.html -->
        <module name="EmptyForIteratorPad"/>
        <module name="GenericWhitespace"/>
        <module name="MethodParamPad"/>
        <module name="NoWhitespaceAfter"/>
        <module name="NoWhitespaceBefore"/>
        <module name="OperatorWrap"/>
        <module name="ParenPad"/>
        <module name="TypecastParenPad"/>
        <module name="WhitespaceAfter"/>
        <module name="WhitespaceAround"/>

        <!-- Modifier Checks                                    -->
        <!-- See https://checkstyle.org/config_modifier.html -->
        <module name="ModifierOrder"/>
        <module name="RedundantModifier"/>

        <!-- Checks for blocks. You know, those {}'s         -->
        <!-- See https://checkstyle.org/config_blocks.html -->
        <module name="AvoidNestedBlocks"/>
        <module name="EmptyBlock"/>
        <module name="LeftCurly"/>
        <module name="NeedBraces"/>
        <module name="RightCurly"/>

        <!-- Checks for common coding problems               -->
        <!-- See https://checkstyle.org/config_coding.html -->
        <module name="EmptyStatement"/>
        <module name="EqualsHashCode"/>
        <module name="HiddenField">
            <property name="ignoreConstructorParameter" value="true"/>
            <property name="ignoreSetter" value="true"/>
            <property name="setterCanReturnItsClass" value="true"/>
            <property name="ignoreAbstractMethods" value="true"/>
        </module>
        <module name="IllegalInstantiation"/>
        <module name="InnerAssignment"/>
        <module name="MagicNumber"/>
        <module name="MissingSwitchDefault"/>
        <module name="MultipleVariableDeclarations"/>
        <module name="RequireThis"/>
        <module name="SimplifyBooleanExpression"/>
        <module name="SimplifyBooleanReturn"/>

        <!-- Checks for class design                         -->
        <!-- See https://checkstyle.org/config_design.html -->
        <module name="DesignForExtension"/>
        <module name="FinalClass"/>
        <module name="HideUtilityClassConstructor"/>
        <module name="InterfaceIsType"/>
        <module name="VisibilityModifier"/>

        <!-- Miscellaneous other checks.                   -->
        <!-- See https://checkstyle.org/config_misc.html -->
        <module name="ArrayTypeStyle"/>
        <module name="FinalParameters"/>
        <module name="TodoComment"/>
        <module name="UpperEll"/>

        <!-- https://checkstyle.org/config_filters.html#SuppressionXpathFilter -->
        <module name="SuppressionXpathFilter">
            <property name="file" value="${org.checkstyle.sun.suppressionxpathfilter.config}"
                      default="checkstyle-xpath-suppressions.xml"/>
            <property name="optional" value="true"/>
        </module>

    </module>

</module>