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="charset" value="UTF-8"/>
    <property name="severity" value="error"/>

    <!-- File-level: enforce newline at end of file -->
    <module name="NewlineAtEndOfFile">
        <property name="lineSeparator" value="lf"/>
    </module>

    <!-- File-level: enforce max line length -->
    <module name="LineLength">
        <property name="max" value="200"/>
        <property name="fileExtensions" value="java"/>
        <property name="ignorePattern" value="^package.*|^import.*|a href|href|http://|https://|ftp://"/>
    </module>

    <module name="TreeWalker">

        <!-- ===== Project-specific: IntelliJ Platform API Usage ===== -->

        <!-- Prohibit use of System.out, System.err, and e.printStackTrace -->
        <module name="RegexpSinglelineJava">
            <property name="format" value="System\.(out|err)\.print|e\.printStackTrace"/>
            <property name="message" value="Do not use System.out/err, use com.intellij.openapi.diagnostic.Logger instead"/>
            <property name="ignoreComments" value="true"/>
        </module>
        <!-- Require ApplicationManager.getApplication().invokeLater instead of SwingUtilities.invokeLater for EDT operations -->
        <module name="RegexpSinglelineJava">
            <property name="format" value="SwingUtilities\.invokeLater"/>
            <property name="message" value="Use ApplicationManager.getApplication().invokeLater instead of SwingUtilities.invokeLater"/>
            <property name="ignoreComments" value="true"/>
        </module>
        <!-- Prohibit System.getProperty("user.home") - use PlatformUtils.getHomeDirectory() instead -->
        <module name="RegexpSinglelineJava">
            <property name="id" value="NoUserHomeProperty"/>
            <property name="format" value="System\.getProperty\(\s*&quot;user\.home&quot;"/>
            <property name="message" value="Do not use System.getProperty(&quot;user.home&quot;), use PlatformUtils.getHomeDirectory() instead (IDEA may override user.home)"/>
            <property name="ignoreComments" value="true"/>
        </module>
        <!-- Allow PlatformUtils.java to use System.getProperty("user.home") as fallback -->
        <module name="SuppressionXpathSingleFilter">
            <property name="id" value="NoUserHomeProperty"/>
            <property name="files" value="PlatformUtils\.java"/>
        </module>

        <!-- ===== Annotations ===== -->

        <!-- Enforce @Override when overriding methods -->
        <module name="MissingOverride"/>

        <!-- ===== Imports ===== -->

        <!-- No illegal imports (e.g. sun.*) -->
        <module name="IllegalImport"/>
        <!-- No duplicate imports or imports of classes in java.lang -->
        <module name="RedundantImport"/>
        <!-- No unused imports -->
        <module name="UnusedImports">
            <property name="processJavadoc" value="true"/>
        </module>

        <!-- ===== Coding (real bug-catchers) ===== -->

        <!-- equals(Object) and equals(SameType) must be consistent -->
        <module name="CovariantEquals"/>
        <!-- Disallow empty statements (lone semicolons) -->
        <module name="EmptyStatement"/>
        <!-- equals() and hashCode() must be overridden together -->
        <module name="EqualsHashCode"/>
        <!-- Simplify boolean expressions such as "x == true" -->
        <module name="SimplifyBooleanExpression"/>
        <!-- Simplify "if (x) return true; else return false;" -->
        <module name="SimplifyBooleanReturn"/>
        <!-- Use .equals() for String comparison, not == -->
        <module name="StringLiteralEquality"/>
        <!-- Declare one variable per declaration statement -->
        <module name="MultipleVariableDeclarations"/>
        <!-- One statement per line -->
        <module name="OneStatementPerLine"/>

        <!-- ===== Miscellaneous ===== -->

        <!-- Use uppercase L for long literals (1000L not 1000l) -->
        <module name="UpperEll"/>
        <!-- Array brackets belong to the type, not the variable (String[] args not String args[]) -->
        <module name="ArrayTypeStyle"/>
        <!-- File name must match the public type name -->
        <module name="OuterTypeFilename"/>

        <!-- ===== Modifiers ===== -->

        <!-- Remove redundant modifiers (e.g. public on interface methods) -->
        <module name="RedundantModifier"/>

        <!-- ===== Block Style ===== -->

        <!-- Require braces around all if/else/while/for/do bodies. Guards against
             goto-fail-style bugs where a future edit silently slips outside the
             conditional. The 197 pre-existing single-line violations were fixed
             in the preceding commit. -->
        <module name="NeedBraces"/>

        <!-- ===== Regexp ===== -->

        <!--
            Forbid single-element array hack used to smuggle mutable state into lambdas / anonymous
            classes, e.g.: final boolean[] flag = {false}; final int[] count = {0};
            Prefer AtomicBoolean / AtomicInteger / AtomicLong / AtomicReference.
        -->
        <module name="RegexpSinglelineJava">
            <property name="format"
                      value="^\s*(?:final\s+)?[A-Za-z_][\w&lt;&gt;,?\s]*\s*\[\]\s+[a-z]\w*\s*=\s*\{\s*[^,{}]+\s*\}"/>
            <property name="message"
                      value="Do not use a single-element array to capture mutable state in a lambda or anonymous class. Use AtomicBoolean / AtomicInteger / AtomicLong / AtomicReference instead."/>
            <property name="ignoreComments" value="true"/>
        </module>
        <module name="RegexpSinglelineJava">
            <property name="format"
                      value="^\s*(?:final\s+)?[A-Za-z_][\w&lt;&gt;,?\s]*\s*\[\]\s+[a-z]\w*\s*=\s*\{\s*new\s+[A-Za-z_][\w&lt;&gt;,?\s]*\s*\[\]\s*\{\s*[^,{}]+\s*\}"/>
            <property name="message"
                      value="Do not use a single-element array to capture mutable state in a lambda or anonymous class. Use AtomicBoolean / AtomicInteger / AtomicLong / AtomicReference instead."/>
            <property name="ignoreComments" value="true"/>
        </module>

        <!--
            ===== Disabled Rules (kept here for future adoption) =====

            The following rules from checkstyle-new.xml are intentionally left out
            for now because they would create a large backlog of fixes. Enable them
            in a future cleanup pass when the team is ready.

            - JavadocMethod / JavadocVariable / JavadocStyle / NonEmptyAtclauseDescription  (~1216 violations)
              Reason: requires writing Javadoc for every public method/field. High effort, low return for
              this project where method names are self-documenting.

            - InnerTypeLastCheck  (~628 violations)
              Reason: pure code-ordering preference, no functional benefit.

            - NestedIfDepth / NestedTryDepth  (~26 violations)
              Reason: real refactoring required, schedule separately.

            - HideUtilityClassConstructor  (~23 violations)
              Reason: needs adding private constructors to all utility classes.

            - LeftCurly / RightCurly / WhitespaceAround / WhitespaceAfter / NoWhitespaceBefore /
              NoWhitespaceAfter / ParenPad / MethodParamPad / GenericWhitespace / AnnotationLocation /
              AvoidNestedBlocks / EmptyBlock  (collectively ~70 violations)
              Reason: stylistic, IDE-fixable. Worth a one-shot reformat in a separate commit.

            - InterfaceIsType / InnerAssignment / OneTopLevelClass
              Reason: project-specific exceptions exist; review case by case before enabling.

            - Trailing whitespace
              Reason: easy to enable after a one-time reformat of all files.
        -->

    </module>
</module>