checkstyle.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE module PUBLIC
        "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
        "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">

<!-- This is a checkstyle configuration file. For descriptions of
what the following rules do, please see the checkstyle configuration
page at http://checkstyle.sourceforge.net/config.html -->

<!-- Checks with numbered comments refer to recommendations made
by Joshua Bloch in his book Effective Java -->

<module name="Checker">
    <!-- java file header needs to contain the license -->
    <module name="RegexpHeader">
        <!-- This file makes minimal use of regular expression; only the year of
             the copy right date has any flexibility outside a strict character-by
             character direct match. -->
        <property name="headerFile" value="${checkstyle.header.file}"/>
        <property name="fileExtensions" value="java"/>
    </module>

    <!-- property name="charset" value="UTF-8"/ -->
    <module name="FileTabCharacter">
        <!-- Checks that there are no tab characters in the file.
        -->
    </module>

    <module name="RegexpSingleline">
        <!-- Checks that FIXME is not used in comments.  TODO is preferred.
        -->
        <property name="format" value="((//.*)|(\*.*))FIXME"/>
        <property name="message"
                  value='TODO is preferred to FIXME.  e.g. "TODO(johndoe): Refactor when v2 is released."'/>
    </module>

    <module name="RegexpSingleline">
        <!-- Checks that TODOs are properly formatted.

             The (?&lt;!TODO\(.{0,120}) makes the regex ignore any secondary TODO's on the line
             so that things like //TODO(bob): remove this TODO on 1/1/2020 don't trigger a warning
             because of the second TODO.  (The {0,120} is because java doesn't recognize arbitrary
             length look backs, but we know each java line should be < 120 chars.)
        -->
        <property name="format" value="((//.*)|(\*.*))(?&lt;!TODO\(.{0,120})(TODO[^(])|(TODO\([^)]*$)"/>
        <property name="message"
                  value='All TODOs should be named.  e.g. "TODO(johndoe): Refactor when v2 is released."'/>
    </module>


    <!-- All Java AST specific tests live under TreeWalker module. -->
    <module name="TreeWalker">

        <!--

        IMPORT CHECKS

        -->

        <module name="RedundantImport">
            <!-- Checks for redundant import statements. -->
            <property name="severity" value="error"/>
        </module>

        <module name="UnusedImports">
            <!-- Checks for unused import statements. -->
            <!-- DPL is a notable violator of this rule. -->
            <property name="severity" value="error"/>
        </module>

        <module name="ImportOrder">
            <!-- Checks for out of order import statements. -->
            <property name="groups" value="/^javax?\./,org"/>
            <property name="ordered" value="true"/>
            <property name="separated" value="true"/>
            <property name="option" value="above"/>
        </module>

        <!--

        JAVADOC CHECKS

        -->

        <module name="JavadocType">
            <!-- Item 28 - Write doc comments for all exposed API elements. -->
            <!-- Ensure all classes with visability greater than or equal to
              protected have class level documentation. -->
            <property name="scope" value="protected"/>
            <property name="severity" value="error"/>
        </module>

        <!--

        NAMING CHECKS

        -->

        <!-- Item 38 - Adhere to generally accepted naming conventions -->

        <module name="PackageName">
            <!-- Validates identifiers for package names against the
              supplied expression. -->
            <property name="format" value="^[a-z]+(\.[a-z][a-z0-9]{1,})*$"/>
            <property name="severity" value="warning"/>
        </module>

        <module name="TypeNameCheck">
            <!-- Validates static, final fields against the
            expression "^[A-Z][a-zA-Z0-9]*$". -->
            <metadata name="altname" value="TypeName"/>
            <property name="severity" value="warning"/>
        </module>

        <module name="ParameterName">
            <!-- Validates identifiers for method parameters against the
              expression "^[a-z][a-zA-Z0-9]*$". -->
            <property name="severity" value="warning"/>
        </module>

        <module name="LocalFinalVariableName">
            <!-- Validates identifiers for local final variables against the
              expression "^[a-z][a-zA-Z0-9]*$". -->
            <property name="severity" value="warning"/>
        </module>

        <module name="LocalVariableName">
            <!-- Validates identifiers for local variables against the
              expression "^[a-z][a-zA-Z0-9]*$". -->
            <property name="severity" value="warning"/>
        </module>


        <!--

        LENGTH and CODING CHECKS

        -->

        <module name="LineLength">
            <!-- Checks if a line is too long. -->
            <property name="max" value="${com.puppycrawl.tools.checkstyle.checks.sizes.LineLength.max}" default="80"/>
            <property name="severity" value="error"/>

            <!--
              The default ignore pattern exempts the following elements:
                - import statements
                - long URLs inside comments
            -->

            <property name="ignorePattern"
                      value="${com.puppycrawl.tools.checkstyle.checks.sizes.LineLength.ignorePattern}"
                      default="^(package .*;\s*)|(import .*;\s*)|( *\* *https?://.*)|(\s*@[\w\.\$]+::\w+(?:\([^\(]*\)|\(\)\(\))?[,;]?)|(\s+\* \{@(link|see) [^\s][^\}]*\})$"/>
        </module>

        <module name="LeftCurly">
            <!-- Checks for placement of the left curly brace ('{'). -->
            <property name="severity" value="warning"/>
        </module>

        <module name="RightCurly">
            <!-- Checks right curlies on CATCH, ELSE, and TRY blocks are on
            the same line. e.g., the following example is fine:
            <pre>
              if {
                ...
              } else
            </pre>
            -->
            <!-- This next example is not fine:
            <pre>
              if {
                ...
              }
              else
            </pre>
            -->
            <property name="option" value="same"/>
            <property name="severity" value="warning"/>
        </module>

        <!-- Checks for braces around if and else blocks -->
        <module name="NeedBraces">
            <property name="severity" value="warning"/>
            <property name="tokens" value="LITERAL_IF, LITERAL_ELSE, LITERAL_FOR, LITERAL_WHILE, LITERAL_DO"/>
        </module>

        <module name="UpperEll">
            <!-- Checks that long constants are defined with an upper ell.-->
            <property name="severity" value="error"/>
        </module>

        <module name="FallThrough">
            <!-- Warn about falling through to the next case statement.  Similar to
            javac -Xlint:fallthrough, but the check is suppressed if a single-line comment
            on the last non-blank line preceding the fallen-into case contains 'fall through' (or
            some other variants which we don't publicized to promote consistency).
            -->
            <property name="reliefPattern"
                      value="fall through|Fall through|fallthru|Fallthru|falls through|Falls through|fallthrough|Fallthrough|No break|NO break|no break|continue on"/>
            <property name="severity" value="error"/>
        </module>


        <!--

        MODIFIERS CHECKS

        -->

        <module name="ModifierOrder">
            <!-- Warn if modifier order is inconsistent with JLS3 8.1.1, 8.3.1, and
                 8.4.3.  The prescribed order is:
                 public, protected, private, abstract, static, final, transient, volatile,
                 synchronized, native, strictfp
              -->
        </module>


        <!--

        WHITESPACE CHECKS

        -->

        <module name="WhitespaceAround">
            <!-- Checks that various tokens are surrounded by whitespace.
                 This includes most binary operators and keywords followed
                 by regular or curly braces.
            -->
            <property name="tokens" value="ASSIGN, BAND, BAND_ASSIGN, BOR,
        BOR_ASSIGN, BSR, BSR_ASSIGN, BXOR, BXOR_ASSIGN, COLON, DIV, DIV_ASSIGN,
        EQUAL, GE, GT, LAND, LE, LITERAL_CATCH, LITERAL_DO, LITERAL_ELSE,
        LITERAL_FINALLY, LITERAL_FOR, LITERAL_IF, LITERAL_RETURN,
        LITERAL_SYNCHRONIZED, LITERAL_TRY, LITERAL_WHILE, LOR, LT, MINUS,
        MINUS_ASSIGN, MOD, MOD_ASSIGN, NOT_EQUAL, PLUS, PLUS_ASSIGN, QUESTION,
        SL, SL_ASSIGN, SR_ASSIGN, STAR, STAR_ASSIGN"/>
            <property name="severity" value="error"/>
        </module>

        <module name="WhitespaceAfter">
            <!-- Checks that commas, semicolons and typecasts are followed by
                 whitespace.
            -->
            <property name="tokens" value="COMMA, SEMI, TYPECAST"/>
        </module>

        <module name="NoWhitespaceAfter">
            <!-- Checks that there is no whitespace after various unary operators.
                 Linebreaks are allowed.
            -->
            <property name="tokens" value="BNOT, DEC, DOT, INC, LNOT, UNARY_MINUS,
        UNARY_PLUS"/>
            <property name="allowLineBreaks" value="true"/>
            <property name="severity" value="error"/>
        </module>

        <module name="NoWhitespaceBefore">
            <!-- Checks that there is no whitespace before various unary operators.
                 Linebreaks are allowed.
            -->
            <property name="tokens" value="SEMI, DOT, POST_DEC, POST_INC"/>
            <property name="allowLineBreaks" value="true"/>
            <property name="severity" value="error"/>
        </module>

        <module name="ParenPad">
            <!-- Checks that there is no whitespace before close parens or after
                 open parens.
            -->
            <property name="severity" value="warning"/>
        </module>

        <!--

        MISC CHECKS

        -->
    </module>
</module>