Improve quality and syntax of your Android code

build.gradle

apply plugin: 'checkstyle'

task checkstyle(type: Checkstyle) {
    configFile rootProject.file('checkstyle.xml')
    source 'src/main/java'
    ignoreFailures false
    showViolations true
    include '**/*.java'

    classpath = files()
}

Checkstyle.md

Checkstyle is a development tool to help programmers write Java code that adheres to a coding standard. It automates the process of checking Java code to spare humans of this boring (but important) task.

Add below code to your project and then launch the task checkstyle from the gradle panel

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">
    <!--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>

    <!-- Space after 'for' and 'if' -->
    <module name="RegexpSingleline">
        <property name="format" value="^\s*(for|if)[^ ]"/>
        <property name="message" value="Space needed before opening parenthesis."/>
    </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">
        <!--<property name="cacheFile" value="${checkstyle.cache.file}"/>-->

        <!-- Checks for Javadoc comments.                     -->
        <!-- See http://checkstyle.sf.net/config_javadoc.html -->
        <!--module name="JavadocMethod"/-->
        <!--module name="JavadocType"/-->
        <!--module name="JavadocVariable"/-->
        <!--module name="JavadocStyle"/-->


        <!-- Checks for Naming Conventions.                  -->
        <!-- See http://checkstyle.sf.net/config_naming.html -->
        <module name="ConstantName"/>
        <module name="LocalFinalVariableName"/>
        <module name="LocalVariableName"/>
        <module name="MemberName"/>
        <module name="MethodName">
            <property name="format" value="^[a-z][a-zA-Z0-9_]*$"/>
        </module>
        <module name="PackageName"/>
        <module name="ParameterName"/>
        <module name="StaticVariableName"/>
        <module name="TypeName">
            <property name="format" value="^[A-Z][a-zA-Z0-9_]*$"/>
        </module>


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


        <!-- Checks for Size Violations.                    -->
        <!-- See http://checkstyle.sf.net/config_sizes.html -->
        <module name="LineLength">
            <property name="max" value="100"/>
        </module>
        <!--<module name="MethodLength"/>-->
        <module name="ParameterNumber"/>


        <!-- Checks for whitespace                               -->
        <!-- See http://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 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"/>
        <module name="LeftCurly"/>
        <module name="NeedBraces">
            <property name="tokens" value="LITERAL_DO, LITERAL_ELSE, LITERAL_FOR, LITERAL_WHILE"/>
        </module>
        <module name="RightCurly"/>


        <!-- Checks for common coding problems               -->
        <!-- See http://checkstyle.sf.net/config_coding.html -->
        <!--<module name="AvoidInlineConditionals"/>-->
        <module name="CovariantEquals"/>
        <!--<module name="DoubleCheckedLocking"/>-->
        <module name="EmptyStatement"/>
        <module name="EqualsAvoidNull"/>
        <module name="EqualsHashCode"/>
        <!--<module name="HiddenField"/>-->
        <module name="IllegalInstantiation"/>
        <module name="InnerAssignment"/>
        <!--<module name="MagicNumber"/>-->
        <module name="MissingSwitchDefault"/>
        <module name="RedundantThrows"/>
        <module name="SimplifyBooleanExpression"/>
        <module name="SimplifyBooleanReturn"/>

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


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