checkstyle.xml

<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
    "-//Puppy Crawl//DTD Check Configuration 1.2//EN"
    "https://www.puppycrawl.com/dtds/configuration_1_2.dtd">


<!-- THIS CHECKSYTLE CONFIGURATION IS SIMILAR TO THE ONE USED BY SQUARE INC. IF YOU WANT TO
     CONFIGURE YOUR IDE TO USE THIS CHECKSTYLE TAKE A LOOK AT https://github.com/square/java-code-styles-->


<module name="Checker">
  <!--module name="NewlineAtEndOfFile"/-->
  <module name="FileLength"/>
  <module name="FileTabCharacter"/>

  <!-- Trailing spaces -->
  <module name="RegexpSingleline">
    <property name="format" value="\s+$"/>
    <property name="message" value="Line has trailing spaces."/>
  </module>

  <!-- For each spacing -->
  <module name="RegexpSingleline">
    <property name="format" value="^\s*for \(.*?([^ ]:|:[^ ])"/>
    <property name="message" value="Space needed around ':' character."/>
  </module>

  <module name="TreeWalker">

    <!-- Checks for Naming Conventions.                  -->
    <!-- See https://checkstyle.sf.net/config_naming.html -->
    <module name="MethodName">
      <property name="format" value="^[a-z](_?[a-zA-Z0-9]+)*$" />
    </module>
    <module name="PackageName"/>
    <module name="ParameterName"/>
    <module name="TypeName"/>
    <module name="ConstantName"/>

    <!-- Checks for imports                              -->
    <!-- See https://checkstyle.sf.net/config_import.html -->
    <module name="AvoidStarImport"/>
    <module name="IllegalImport"/>
    <!-- defaults to sun.* packages -->
    <module name="RedundantImport"/>
    <module name="UnusedImports">
      <property name="processJavadoc" value="true"/>
    </module>

    <!-- Checks for Size Violations.                    -->
    <!-- See https://checkstyle.sf.net/config_sizes.html -->
    <module name="LineLength">
      <property name="max" value="120"/>
    </module>

    <!-- Checks for whitespace                               -->
    <!-- See https://checkstyle.sf.net/config_whitespace.html -->
    <module name="GenericWhitespace"/>
    <module name="EmptyForIteratorPad"/>
    <module name="MethodParamPad"/>
    <module name="NoWhitespaceAfter"/>
    <module name="NoWhitespaceBefore"/>
    <module name="OperatorWrap"/>
    <module name="ParenPad"/>
    <module name="TypecastParenPad"/>
    <module name="WhitespaceAfter"/>
    <module name="WhitespaceAround"/>

    <!-- Modifier Checks                                    -->
    <!-- See https://checkstyle.sf.net/config_modifiers.html -->
    <module name="RedundantModifier"/>

    <!-- Checks for blocks. You know, those {}'s         -->
    <!-- See https://checkstyle.sf.net/config_blocks.html -->
    <module name="LeftCurly"/>
    <!--<module name="NeedBraces"/>-->
    <module name="RightCurly"/>

    <!-- Checks for common coding problems               -->
    <!-- See https://checkstyle.sf.net/config_coding.html -->
    <module name="CovariantEquals"/>
    <module name="EmptyStatement"/>
    <module name="EqualsHashCode"/>
    <module name="IllegalInstantiation"/>
    <module name="MissingSwitchDefault"/>
    <module name="SimplifyBooleanExpression"/>
    <module name="SimplifyBooleanReturn"/>

    <!-- Miscellaneous other checks.                   -->
    <!-- See https://checkstyle.sf.net/config_misc.html -->
    <module name="UpperEll"/>
  </module>
</module>