src/conf/checkstyle.xml

<?xml version="1.0"?>
<!--
Licensed to the Apache Software Foundation (ASF) under one or more
contributor license agreements.  See the NOTICE file distributed with
this work for additional information regarding copyright ownership.
The ASF licenses this file to You under the Apache License, Version 2.0
(the "License"); you may not use this file except in compliance with
the License.  You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
-->

<!DOCTYPE module PUBLIC
    "-//Checkstyle//DTD Checkstyle Configuration 1.2//EN"
    "https://checkstyle.org/dtds/configuration_1_2.dtd">

<!-- commons codec customization of default Checkstyle behavior -->
<module name="Checker">
  <property name="localeLanguage" value="en" />

  <!-- Checks whether files end with a new line. -->
  <!-- See http://checkstyle.sf.net/config_misc.html#NewlineAtEndOfFile -->
  <module name="NewlineAtEndOfFile" />

  <!-- Checks for Tab characters -->
  <!-- See http://checkstyle.sourceforge.net/config_whitespace.html#FileTabCharacter -->
  <module name="FileTabCharacter">
    <property name="fileExtensions" value="java" />
  </module>

  <!-- Checks for white space at the end of the line -->
  <!-- See http://checkstyle.sourceforge.net/config_regexp.html -->
  <!-- 706
  <module name="RegexpSingleline">
    <property name="format" value="\s+$" />
    <property name="message" value="Line has trailing spaces." />
    <property name="fileExtensions" value="java" />
  </module>
  -->

  <!-- @author tags are deprecated -->
  <module name="RegexpSingleline">
    <property name="format" value="^\s+\*\s+@author\s" />
    <property name="message" value="Deprecated @author tag" />
    <property name="fileExtensions" value="java" />
    <property name="severity" value="warning" />
  </module>

  <module name="TreeWalker">
    <property name="cacheFile" value="target/cachefile" />
    <!-- 
     -->
    <module name="LineLength">
      <property name="max" value="160"/>
    </module>
 
    <!-- Checks for Naming Conventions.                  -->
    <!-- See http://checkstyle.sf.net/config_naming.html -->
    <!-- allow CONSTANT_Long etc -->
    <!-- 
    <module name="ConstantName">
      <property name="format" value="^[A-Z][A-Z0-9]*(_[A-Za-z0-9]+)*$"/>
    </module>
    <module name="LocalFinalVariableName"/>
    <module name="LocalVariableName"/>
    <module name="MemberName">
      <property name="format" value="^[a-z][a-zA-Z0-9_]*(_[a-zA-Z0-9]+)*$"/>
    </module>
    <module name="MethodName"/>
    <module name="PackageName"/>
    <module name="ParameterName"/>
    <module name="StaticVariableName"/>
     -->
    <module name="TypeName">
        <!-- Allow underscore in class names -->
        <property name="format" value="^[A-Z][A-Za-z0-9]*(_[A-Za-z0-9]+)*$"/>
    </module>

    <!-- Checks for imports                              -->
    <!-- See http://checkstyle.sf.net/config_imports.html -->
    <module name="AvoidStarImport">
        <property name="excludes" value="org.junit.Assert"/>
    </module>
    <module name="IllegalImport"/> <!-- defaults to sun.* packages -->
    <module name="RedundantImport"/>
    <module name="UnusedImports"/>
    
    <!-- Checks for whitespace                               -->
    <!-- See http://checkstyle.sf.net/config_whitespace.html -->
    <module name="EmptyForIteratorPad"/>
    <!-- Too many to fix at present
    <module name="NoWhitespaceAfter"/>
    <module name="NoWhitespaceBefore"/>
    <module name="OperatorWrap">
      <property name="option" value="nl" />
    </module>
    -->
    <!-- Too many to fix at present
    <module name="ParenPad"/>
    <module name="WhitespaceAfter"/>
    <module name="WhitespaceAround"/>
    -->
    
    <!-- Modifier Checks                                    -->
    <!-- See http://checkstyle.sf.net/config_modifiers.html -->
    <module name="ModifierOrder"/>
    
    <!--module name="RedundantModifier"/-->
    
    <!-- Checks for blocks. You know, those {}'s         -->
    <!-- See http://checkstyle.sf.net/config_blocks.html -->
    <!--module name="AvoidNestedBlocks"/-->
    <module name="EmptyBlock">
      <property name="option" value="text"/>
    </module>
    <!--
    <module name="LeftCurly">
        <property name="option" value="nl"/>
    </module>
    -->
    <module name="NeedBraces"/>
    <!--
    <module name="RightCurly">
        <property name="option" value="alone"/>
    </module>
    -->
    
    <!-- Checks for common coding problems               -->
    <!-- See http://checkstyle.sf.net/config_coding.html -->
    <module name="CovariantEquals"/>
    <module name="EqualsHashCode"/>
    <module name="IllegalInstantiation"/>
    <!--module name="InnerAssignment"/--><!-- Inner assignments are OK -->
    <!-- module name="MagicNumber">
        <property name="ignoreNumbers" value="-1,0,1,2,3"/>
    </module-->
    <module name="SimplifyBooleanExpression"/>
    <module name="SimplifyBooleanReturn"/>
    <module name="StringLiteralEquality"/>
    <!--module name="SuperClone"/-->
    <module name="SuperFinalize"/>
    <!--module name="DeclarationOrder"/-->
    <!--module name="ExplicitInitialization"/-->
    <module name="DefaultComesLast"/>
    <module name="FallThrough">
        <property name="reliefPattern" value="\$FALL-THROUGH\$"/><!-- to agree with Eclipse -->
    </module>
    <module name="MultipleVariableDeclarations"/>
    <module name="UnnecessaryParentheses"/>

    <!-- Checks for class design                         -->
    <!-- See http://checkstyle.sf.net/config_design.html -->
    <!--module name="FinalClass"/-->
    <!--module name="HideUtilityClassConstructor"/-->
    <!--module name="InterfaceIsType"/-->

    <module name="VisibilityModifier">
        <property name="ignoreAnnotationCanonicalNames" value="java.lang.Deprecated"/>
        <property name="protectedAllowed" value="false"/>
        <property name="packageAllowed" value="true"/>
    </module>
    
    <!-- Miscellaneous other checks.                   -->
    <!-- See http://checkstyle.sf.net/config_misc.html -->
    <module name="ArrayTypeStyle"/>
    <!--module name="TodoComment"/-->
    <module name="UpperEll"/>
    
    <!-- Required for SuppressionCommentFilter below -->
    <module name="FileContentsHolder"/>

  </module>

  <module name="SuppressionCommentFilter"/>

  <module name="SuppressionFilter">
    <!-- config_loc is used by Eclipse plugin -->
    <property name="file" value="${config_loc}/src/conf/checkstyle-suppressions.xml"/>
  </module>

  <!-- 
      Allow comment to suppress checkstyle for a single line
      e.g. // CHECKSTYLE IGNORE MagicNumber
   -->
  <module name="SuppressWithNearbyCommentFilter">
    <property name="commentFormat" value="CHECKSTYLE IGNORE (\w+)"/>
    <property name="checkFormat" value="$1"/>
  </module>

</module>