build-tools/src/main/resources/build-tools/checkstyle/checker.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--
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.
-->

<!--
  This version of checkstyle is based on the Apache Calcite checkstyle
  configuration, which in turn is based on Giraph, Hadoop, and
  common-math configurations.

  The documentation for checkstyle is available at

  http://checkstyle.sourceforge.net
-->

<!DOCTYPE module PUBLIC "-//Puppy Crawl//DTD Check Configuration 1.1//EN"
        "http://www.puppycrawl.com/dtds/configuration_1_1.dtd">

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

    <!-- Checks for whitespace (tree walker)                 -->
    <!-- See http://checkstyle.sf.net/config_whitespace.html -->
    <!-- No tabs allowed! -->
    <module name="FileTabCharacter"/>

    <!-- Checks for headers -->
    <!-- See http://checkstyle.sf.net/config_header.html -->
    <!-- Verify that EVERY source file has the appropriate license -->
    <module name="Header">
        <property name="header" value="/*\n"/>
        <property name="fileExtensions" value="java"/>
    </module>

    <module name="TreeWalker">
        <!-- Checks for blocks. You know, those {}'s         -->
        <!-- See http://checkstyle.sf.net/config_blocks.html -->
        <!-- No empty blocks (i.e. catch); must contain at least a comment -->
        <module name="EmptyBlock">
            <property name="option" value="text"/>
        </module>
        <module name="AvoidNestedBlocks">
            <property name="allowInSwitchCase" value="true"/>
        </module>

        <!-- Checks for common coding problems               -->
        <!-- See http://checkstyle.sf.net/config_coding.html -->
        <module name="EmptyStatement"/>
        <!-- Require hash code override when equals is -->
        <module name="EqualsHashCode"/>
        <!-- Enforce array type style -->
        <module name="ArrayTypeStyle"/>
        <!-- Constant on left of equals -->
        <module name="EqualsAvoidNullCheck"/>
        <!-- Disallow unnecessary instantiation of Boolean, String -->
        <module name="IllegalInstantiation">
            <property name="classes" value="java.lang.Boolean"/>
        </module>
        <!-- Switch statements should be complete and with independent cases -->
        <!--<module name="FallThrough"/>-->
        <module name="SimplifyBooleanExpression"/>
        <module name="SimplifyBooleanReturn"/>
        <!-- Only one statement per line allowed -->
        <!--<module name="OneStatementPerLine"/>-->
        <!-- Don't add up parentheses when they are not required -->
        <!--<module name="UnnecessaryParentheses"/>-->
        <!-- Don't use = or != for string comparisons -->
        <module name="StringLiteralEquality"/>
        <!-- Don't declare multiple variables in the same statement -->
        <!--<module name="MultipleVariableDeclarations"/>-->
        <!-- Make sure @Override annotation is on methods -->
        <module name="MissingOverride"/>
        
        <!-- Checks for imports                              -->
        <!-- See http://checkstyle.sf.net/config_import.html -->
        <module name="RedundantImport"/>
        <!-- Import should be explicit, and only from pure java packages.
             But we allow imports that are only used in javadoc. -->
        <module name="UnusedImports">
            <property name="processJavadoc" value="true"/>
        </module>
        <module name="IllegalImport"/>
        <module name="AvoidStarImport"/>

        <module name="UpperEll"/>
        <module name="ModifierOrder"/>
        <module name="RedundantModifier"/>
        <module name="Regexp">
            <property name="format" value="[ \t]+$"/>
            <property name="illegalPattern" value="true"/>
            <property name="message" value="Trailing whitespace"/>
        </module>
    </module>
</module>