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">
  <property name="severity" value="error"/>
  <property name="fileExtensions" value="java"/>

  <!-- No tab characters -->
  <module name="FileTabCharacter"/>

  <!-- No trailing whitespace -->
  <module name="RegexpSingleline">
    <property name="format" value="\s+$"/>
    <property name="message" value="Line has trailing whitespace."/>
  </module>

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

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

    <!-- Code quality -->
    <module name="EmptyBlock">
      <property name="option" value="text"/>
    </module>
    <module name="NeedBraces"/>
    <module name="EqualsHashCode"/>
    <module name="SimplifyBooleanExpression"/>
    <module name="SimplifyBooleanReturn"/>
    <module name="StringLiteralEquality"/>
    <module name="MissingSwitchDefault"/>
    <module name="DefaultComesLast"/>
    <module name="FallThrough"/>

    <!-- Whitespace -->
    <module name="WhitespaceAround"/>
    <module name="WhitespaceAfter"/>
    <module name="NoWhitespaceBefore"/>
    <module name="MethodParamPad"/>
    <module name="ParenPad"/>

    <!-- Modifiers -->
    <module name="ModifierOrder"/>
    <module name="RedundantModifier"/>
  </module>
</module>