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:
    - 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 -->

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

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

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

    <!-- Miscellaneous other checks.                   -->
    <!-- See https://checkstyle.org/config_misc.html -->

    <!-- 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 -->
        <!-- Checks for imports                              -->
        <!-- See https://checkstyle.org/config_imports.html -->
        <!-- Modifier Checks                                    -->
        <!-- See https://checkstyle.org/config_modifier.html -->
        <!-- Checks for class design                         -->
        <!-- See https://checkstyle.org/config_design.html -->

        <!-- Checks for Naming Conventions.                  -->
        <!-- See https://checkstyle.org/config_naming.html -->
        <module name="AbstractClassName"/>
        <module name="ConstantName"/>


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

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

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

        <!-- Checks for common coding problems               -->
        <!-- See https://checkstyle.org/config_coding.html -->

        <module name="AvoidInlineConditionals"/>
        <module name="DeclarationOrder"/>
        <module name="EmptyStatement"/>
        <module name="MultipleVariableDeclarations"/>
        <module name="NestedForDepth"/>
        <module name="NestedIfDepth"/>
        <module name="NestedTryDepth"/>
        <module name="OneStatementPerLine"/>
        <module name="RequireThis"/>
        <module name="SimplifyBooleanExpression"/>
        <module name="SimplifyBooleanReturn"/>
        <module name="StringLiteralEquality"/>
        <module name="UnnecessaryParentheses"/>
        <module name="UnnecessarySemicolonAfterTypeMemberDeclaration"/>

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

        <!-- Checks for metrics.                             -->
        <!-- See https://checkstyle.org/config_metrics.html -->
        <module name="BooleanExpressionComplexity"/>

        <!-- 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>