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 customized for my code style preferences.

  This configuration enforces the following:
    - Proper indentation (4 spaces)
    - No unnecessary trailing spaces
    - Maximum line length of 120 characters
    - Consistent brace style (Allman)
    - Proper whitespace usage
    - Enforcement of basic Java best practices without adhering strictly to official conventions.
-->

<module name="Checker">

  <module name="SuppressionFilter">
    <property name="file" value="checkstyle_suppression.xml" />
  </module>

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

  <!-- Exclude module-info.java files as they are not needed for validation -->
  <module name="BeforeExecutionExclusionFileFilter">
    <property name="fileNamePattern" value="module-info\.java$"/>
  </module>

  <!-- Ensure files end with a newline -->
  <module name="NewlineAtEndOfFile"/>

  <!-- Enforce maximum file length -->
  <module name="FileLength"/>

  <!-- Maximum line length set to 150 characters -->
  <module name="LineLength">
    <property name="max" value="150"/>
  </module>

  <!-- Disallow tab characters, enforce 4-space indentation -->
  <module name="FileTabCharacter">
    <property name="eachLine" value="true"/>
  </module>

  <module name="TreeWalker">
    <!-- Enforce brace style (K&R), which starts a block on the same line as the control statement -->
    <module name="LeftCurly">
      <property name="option" value="nl"/>
    </module>
    <module name="RightCurly">
      <property name="option" value="alone"/>
    </module>

    <!-- Enforce indentation -->
    <module name="Indentation">
      <property name="basicOffset" value="4"/>
      <property name="braceAdjustment" value="0"/>
      <property name="caseIndent" value="4"/>
      <property name="throwsIndent" value="4"/>
      <property name="lineWrappingIndentation" value="4"/>
      <property name="arrayInitIndent" value="4"/>
    </module>

    <!-- Enforce no empty blocks without comments -->
    <module name="EmptyBlock">
      <property name="option" value="TEXT"/>
      <property name="tokens" value="LITERAL_TRY, LITERAL_FINALLY, LITERAL_IF, LITERAL_ELSE, LITERAL_SWITCH"/>
    </module>

    <!-- Suppression via comments -->
    <module name="SuppressionCommentFilter"/>

    <!-- No unused imports -->
    <module name="UnusedImports"/>

    <!-- Checks for naming conventions -->
    <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"/>

    <!-- Enforce spacing around operators -->
    <module name="WhitespaceAround">
      <property name="allowEmptyConstructors" value="true"/>
      <property name="allowEmptyMethods" value="true"/>
      <property name="allowEmptyTypes" value="true"/>
      <property name="allowEmptyLoops" value="true"/>
      <property name="allowEmptyLambdas" value="true"/>
    </module>

    <!-- Additional whitespace rules to avoid inconsistent formatting -->
    <module name="WhitespaceAfter"/>
    <module name="NoWhitespaceBefore"/>
    <module name="ParenPad"/>

    <!-- Ensure a blank line exists between class definitions and members -->
    <module name="EmptyLineSeparator">
      <property name="allowNoEmptyLineBetweenFields" value="true"/>
    </module>

    <!-- No multiple variable declarations in a single line -->
    <module name="MultipleVariableDeclarations"/>

    <!-- Ensure proper method design and code clarity -->
    <module name="FinalClass"/>
  </module>
</module>