checkstyle.xml

<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
          "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
          "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">

<module name="Checker">

    <!-- Use 4 spaces, not tabs -->
    <module name="FileTabCharacter">
        <property name="eachLine" value="true"/>
    </module>

    <module name="TreeWalker">

        <!-- Java filename must match name of outer class -->
        <module name="OuterTypeFilename"/>

        <!-- Use \n, \b etc. instead of octal or unicode escape (e.g. \012) -->
        <module name="IllegalTokenText">
            <property name="tokens" value="STRING_LITERAL, CHAR_LITERAL"/>
            <property name="format" value="\\u00(08|09|0(a|A)|0(c|C)|0(d|D)|22|27|5(C|c))|\\(0(10|11|12|14|15|42|47)|134)"/>
            <property name="message" value="Avoid using corresponding octal or Unicode escape."/>
        </module>

        <!-- Disallow unicode escapes, except control or non-printable chars -->
        <module name="AvoidEscapedUnicodeCharacters">
            <property name="allowEscapesForControlCharacters" value="true"/>
            <property name="allowByTailComment" value="true"/>
            <property name="allowNonPrintableEscapes" value="true"/>
        </module>

        <!-- Avoid wildcard star imports -->
        <module name="AvoidStarImport"/>

        <!-- Only one top-level class per file -->
        <module name="OneTopLevelClass"/>

        <!-- No line-wrapping on import and package statements, e.g.
        ```
        import long.import.
            .on.many.Lines;
        ```
        -->
        <module name="NoLineWrap"/>

        <!-- No empty blocks allowed -->
        <module name="EmptyBlock"/>

        <!-- In some cases, empty blocks are allowed with a comment inside, e.g.
        This is bad:
        ```
        try {
            doThing();
        } catch (MyException ex) {}
        ```
        This is fine:
        ```
        try {
            doThing();
        } catch (MyException ex) {
            // I'm ignoring this for a good reason, I promise!
        }
        ```
        -->
        <module name="EmptyBlock">
            <property name="option" value="text"/>
            <property name="tokens" value="LITERAL_CATCH, LITERAL_CASE, LITERAL_DEFAULT, ARRAY_INIT"/>
        </module>

        <!-- No multi-line statements without braces, e.g.
        ```
        if (youDoThis)
            maven.willGetAngry();
        ```
        -->
        <module name="NeedBraces">
            <property name="allowSingleLineStatement" value="true"/>
        </module>

        <!-- Allow only one statement per line -->
        <module name="OneStatementPerLine"/>

    </module>

</module>