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/technetwork/java/codeconvtoc-136057.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/5.x/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 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 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 Naming Conventions.                  -->
    <!-- See https://checkstyle.org/config_naming.html -->
    <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"/>

    <!-- Checks for imports                              -->
    <!-- See https://checkstyle.org/config_import.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 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_modifiers.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="IllegalInstantiation"/>
    <module name="InnerAssignment"/>
    <module name="MissingSwitchDefault"/>
    <module name="MultipleVariableDeclarations"/>
    <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>