kemitix-checkstyle-ruleset

Provides an extensive Checkstyle ruleset for use with Checkstyle, together with a fully configured maven-tile.

The ruleset includes checks from both the core Checkstyle library and from the Sevntu-Checkstyle library.

• Usage
• All Checks
• Enabled Checks
  • Checkstyle
  • Sevntu
• Disabled Checks
  • Checkstyle
  • Sevntu

Usage

The simplest way to use the ruleset is with the maven-tile:

<project>
    <properties>
        <tiles-maven-plugin.version>2.11</tiles-maven-plugin.version>
    </properties>
    <build>
        <plugins>
            <plugin>
                <groupId>io.repaint.maven</groupId>
                <artifactId>tiles-maven-plugin</artifactId>
                 <version>${tiles-maven-plugin.version}</version>
                <extensions>true</extensions>
                <configuration>
                    <tiles>
                        <tile>net.kemitix.checkstyle:tile:${version}</tile>
                    </tiles>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

The following levels implement increasingly strict rulesets:

• 0-disabled
• 1-layout
• 2-naming
• 3-javadoc
• 4-tweaks
• 5-complexity

The default ruleset from the maven-tile is 5-complexity. Other levels can be selected by setting the kemitix.checkstyle.ruleset.level to one the values above.

Change from 4.x

The RedundantModifier rule has been replaced by the InterfaceMemberImpliedModifier. This is to ensure that intefaces in Java 9+ are easier to comprehend with the addition of private methods. The rules governing the implied modifiers for members of interfaces differs from those of classes. So, to remove the need to remember the different rules, they are now required to be explicitly stated.

Change from 3.x

Rename the artifact net.kemitix:kemitix-checkstyle-ruleset as net.kemitix.checkstyle:ruleset.

Introduction of the artifact net.kemitix.checkstyle:tile for use with the tiles-maven-plugin.

Change from 2.x

In 2.x, the level was specified as the goal to invoke. In 3.x, there is only the 'check' goal. The level is now specified as a configuration parameter. See the example below. The kemitix-checkstyle-maven-plugin has also been removed in favour of the maven-tile.

All Checks

Rule	Level	Source	Enabled	Suppressible
AbbreviationAsWordInName	naming	checkstyle	Yes
AbstractClassName	naming	checkstyle
AnnotationLocation	layout	checkstyle	Yes
AnnotationUseStyle	layout	checkstyle	Yes
AnonInnerLength	complexity	checkstyle	Yes
ArrayTrailingComma	tweaks	checkstyle
ArrayTypeStyle	layout	checkstyle	Yes
AtclauseOrder	javadoc	checkstyle	Yes
AvoidConditionInversion	complexity	sevntu
AvoidConstantAsFirstOperandInCondition	tweaks	sevntu	Yes
AvoidDefaultSerializableInInnerClasses	tweaks	sevntu	Yes
AvoidDoubleBraceInitialization	tweaks	checkstyle	Yes
AvoidEscapedUnicodeCharacters	tweaks	checkstyle	Yes
AvoidHidingCauseException	tweaks	sevntu	Yes
AvoidInlineConditionals	complexity	checkstyle	Yes
AvoidModifiersForTypes	unspecified	sevntu
AvoidNestedBlocks	complexity	checkstyle	Yes
AvoidNoArgumentSuperConstructorCall	tweaks	checkstyle	Yes
AvoidNotShortCircuitOperatorsForBoolean	tweaks	sevntu	Yes
AvoidStarImport	layout	checkstyle
AvoidStaticImport	complexity	checkstyle
BooleanExpressionComplexity	complexity	checkstyle	Yes
CatchParameterName	naming	checkstyle	Yes
CauseParameterInException	tweaks	sevntu
ChildBlockLength	complexity	sevntu
ClassDataAbstractionCoupling	complexity	checkstyle	Yes
ClassFanOutComplexity	complexity	checkstyle	Yes
ClassTypeParameterName	naming	checkstyle	Yes
CommentsIndentation	layout	checkstyle	Yes
ConfusingCondition	complexity	sevntu	Yes
ConstantName	naming	checkstyle	Yes	No
ConstructorWithoutParams	complexity	sevntu	Yes
CovariantEquals	complexity	checkstyle	Yes	No
CustomDeclarationOrder	layout	sevntu
CyclomaticComplexity	complexity	checkstyle	Yes
DeclarationOrder	layout	checkstyle	Yes
DefaultComesLast	tweaks	checkstyle	Yes
DesignForExtension	complexity	checkstyle	Yes
DiamondOperatorForVariableDefinition	tweaks	sevntu	Yes
EitherLogOrThrow	tweaks	sevntu	Yes
EmptyBlock	tweaks	checkstyle	Yes
EmptyCatchBlock	tweaks	checkstyle	Yes
EmptyForInitializerPad	layout	checkstyle	Yes
EmptyForIteratorPad	layout	checkstyle	Yes
EmptyLineSeparator	layout	checkstyle
EmptyPublicCtorInClass	tweaks	sevntu	Yes
EmptyStatement	layout	checkstyle	Yes
EnumValueName	naming	sevntu	Yes
EqualsAvoidNull	tweaks	checkstyle	Yes
EqualsHashCode	complexity	checkstyle	Yes	No
ExecutableStatementCount	complexity	checkstyle	Yes
ExplicitInitialization	tweaks	checkstyle	Yes
FallThrough	javadoc	checkstyle	Yes
FileLength	complexity	checkstyle	Yes
FileTabCharacter	layout	checkstyle	Yes
FinalClass	complexity	checkstyle	Yes
FinalizeImplementation	tweaks	sevntu	Yes
FinalLocalVariable	tweaks	checkstyle
FinalParameters	tweaks	checkstyle	Yes
ForbidAnnotation	unspecified	sevntu
ForbidCCommentsInMethods	layout	sevntu	Yes
ForbidCertainImports	unspecified	sevntu
ForbidInstantiation	unspecified	sevntu
ForbidReturnInFinallyBlock	complexity	sevntu	Yes
ForbidThrowAnonymousExceptions	tweaks	sevntu
ForbidWildcardAsReturnType	complexity	sevntu	Yes
GenericWhitespace	layout	checkstyle	Yes
Header	layout	checkstyle
HiddenField	tweaks	checkstyle	Yes
HideUtilityClassConstructor	tweaks	checkstyle	Yes
IllegalCatch	tweaks	checkstyle	Yes
IllegalImport	tweaks	checkstyle	Yes
IllegalInstantiation	unspecified	checkstyle
IllegalThrows	tweaks	checkstyle	Yes
IllegalToken	tweaks	checkstyle	Yes
IllegalTokenText	unspecified	checkstyle
IllegalType	tweaks	checkstyle	Yes
ImportControl	unspecified	checkstyle
ImportOrder	layout	checkstyle
Indentation	layout	checkstyle
InnerAssignment	tweaks	checkstyle	Yes
InnerTypeLast	tweaks	checkstyle	Yes
InterfaceIsType	complexity	checkstyle	Yes
InterfaceMemberImpliedModifier	tweaks	checkstyle
InterfaceTypeParameterName	naming	checkstyle	Yes
JavadocMethod	javadoc	checkstyle
JavadocMissingLeadingAsterisk	javadoc	checkstyle	Yes
JavadocMissingWhitespaceAfterAsterisk	javadoc	checkstyle	Yes
JavadocPackage	javadoc	checkstyle	Yes
JavadocParagraph	javadoc	checkstyle	Yes
JavadocStyle	javadoc	checkstyle	Yes
JavadocTagContinuationIndentation	layout	checkstyle
JavadocType	javadoc	checkstyle	Yes
JavadocVariable	javadoc	checkstyle
JavaNCSS	complexity	checkstyle	Yes
LambdaBodyLength	complexity	checkstyle	Yes
LambdaParameterName	naming	checkstyle	Yes
LeftCurly	layout	checkstyle	Yes
LineLength	layout	checkstyle	Yes
LocalFinalVariableName	naming	checkstyle	Yes
LocalVariableName	naming	checkstyle	Yes
LogicConditionNeedOptimization	tweaks	sevntu	Yes
MagicNumber	naming	checkstyle	Yes
MapIterationInForEachLoop	complexity	sevntu	Yes
MemberName	naming	checkstyle	Yes
MethodCount	complexity	checkstyle	Yes
MethodLength	complexity	checkstyle	Yes
MethodName	naming	checkstyle	Yes
MethodParamPad	layout	checkstyle	Yes
MethodTypeParameterName	naming	checkstyle	Yes
MissingCtor	tweaks	checkstyle
MissingDeprecated	javadoc	checkstyle	Yes
MissingOverride	tweaks	checkstyle
MissingSwitchDefault	tweaks	checkstyle	Yes
ModifiedControlVariable	tweaks	checkstyle	Yes
ModifierOrder	naming	checkstyle	Yes
MoveVariableInsideIfCheck	tweaks	sevntu	Yes
MultipleStringLiterals	naming	checkstyle	Yes
MultipleVariableDeclarations	naming	checkstyle	Yes
MutableException	tweaks	checkstyle	Yes
NameConventionForJunit4TestClasses	naming	sevntu	Yes
NeedBraces	naming	checkstyle	Yes
NestedForDepth	complexity	checkstyle	Yes
NestedIfDepth	complexity	checkstyle	Yes
NestedSwitch	complexity	sevntu	Yes
NestedTryDepth	complexity	checkstyle	Yes
NewlineAtEndOfFile	layout	checkstyle	Yes
NoClone	tweaks	checkstyle	Yes	No
NoCodeInFile	layout	checkstyle	Yes
NoFinalizer	tweaks	checkstyle	Yes
NoLineWrap	layout	checkstyle	Yes
NoMainMethodInAbstractClass	tweaks	sevntu	Yes
NonEmptyAtclauseDescription	javadoc	checkstyle	Yes
NoWhitespaceAfter	layout	checkstyle	Yes
NoWhitespaceBefore	layout	checkstyle	Yes
NoWhitespaceBeforeCaseDefaultColon	layout	checkstyle	Yes
NPathComplexity	complexity	checkstyle	Yes
NumericLiteralNeedsUnderscore	naming	sevntu	Yes
OneStatementPerLine	layout	checkstyle	Yes
OneTopLevelClass	tweaks	checkstyle	Yes	No
OperatorWrap	layout	checkstyle	Yes
OuterTypeFilename	tweaks	checkstyle	Yes	No
OuterTypeNumber	tweaks	checkstyle
OverloadMethodsDeclarationOrder	layout	checkstyle	Yes
OverridableMethodInConstructor	tweaks	sevntu	Yes
PackageAnnotation	tweaks	checkstyle	Yes
PackageDeclaration	javadoc	checkstyle	Yes	No
PackageName	naming	checkstyle	Yes
ParameterAssignment	tweaks	checkstyle
ParameterName	naming	checkstyle	Yes
ParameterNumber	complexity	checkstyle	Yes
ParenPad	layout	checkstyle	Yes
PublicReferenceToPrivateType	tweaks	sevntu	Yes
RedundantImport	layout	checkstyle
RedundantModifier	tweaks	checkstyle
RedundantReturn	tweaks	sevntu	Yes
Regexp	unspecified	checkstyle
RegexpHeader	unspecified	checkstyle
RegexpMultiline	unspecified	checkstyle
RegexpOnFilename	layout	checkstyle	Yes
RegexpOnFilename	unspecified	checkstyle
RegexpSingleline	unspecified	checkstyle
RegexpSinglelineJava	unspecified	checkstyle
RequiredParameterForAnnotation	unspecified	sevntu
RequireThis	tweaks	checkstyle	Yes
ReturnBooleanFromTernary	tweaks	sevntu	Yes
ReturnCount	complexity	checkstyle	Yes
ReturnNullInsteadOfBoolean	tweaks	sevntu	Yes
RightCurly	layout	checkstyle	Yes
SeparatorWrap	layout	checkstyle	Yes
SimpleAccessorNameNotation	naming	sevntu
SimplifyBooleanExpression	complexity	checkstyle	Yes
SimplifyBooleanReturn	complexity	checkstyle	Yes
SingleBreakOrContinue	tweaks	sevntu	Yes
SingleLineJavadoc	javadoc	checkstyle
SingleSpaceSeparator	layout	checkstyle	Yes
StaticMethodCandidate	unspecified	sevntu
StaticVariableName	naming	checkstyle	Yes
StringLiteralEquality	tweaks	checkstyle	Yes
SummaryJavadoc	javadoc	checkstyle
SuperClone	tweaks	checkstyle
SuperFinalize	tweaks	checkstyle
SuppressWarnings	naming	checkstyle	Yes
SuppressWarningsFilter	naming	checkstyle	Yes
SuppressWarningsHolder	naming	checkstyle	Yes
TernaryPerExpressionCount	tweaks	sevntu	Yes
ThrowsCount	complexity	checkstyle	Yes
TodoComment	javadoc	checkstyle	Yes
TrailingComment	layout	checkstyle	Yes
Translation	javadoc	checkstyle	Yes
TypecastParenPad	layout	checkstyle	Yes
TypeName	naming	checkstyle	Yes	No
UncommentedMain	javadoc	checkstyle	Yes
UniformEnumConstantName	naming	sevntu	Yes
UniqueProperties	javadoc	checkstyle	Yes
UnnecessaryParentheses	layout	checkstyle	Yes
UnnecessarySemicolonAfterOuterTypeDeclaration	layout	checkstyle	Yes
UnusedImports	layout	checkstyle	Yes
UpperEll	layout	checkstyle	Yes
UselessSingleCatch	tweaks	sevntu	Yes
UselessSuperCtorCall	tweaks	sevntu	Yes
VariableDeclarationUsageDistance	tweaks	checkstyle	Yes
VisibilityModifier	tweaks	checkstyle	Yes	No
WhitespaceAfter	layout	checkstyle	Yes
WhitespaceAround	layout	checkstyle	Yes
WhitespaceBeforeArrayInitializer	layout	sevntu	Yes
WriteTag	unspecified	checkstyle

Enabled Checks

The following is a list of each of the checks and the expectations each has on your code.

Checkstyle

Rules are listed in alphabetical order.

AbbreviationAsWordInName

Enforces proper CamelCase and avoids sequences of consecutive uppercase characters in identifiers. Does not apply to @Overridden methods.

Valid:

class DaoManager {}

Invalid:

class DAOManager {}

AnnotationLocation

Annotations must be on a line by themselves unless annotating a method parameter or among class modifiers.

Valid:

@Component
@Qualifier("Red")
class RedStick implements Stick {

    public @NonNull String getLabel(@Value("${stick.length}") final int length) {
        // ...
    }
}

Invalid:

@Component @Qualifier("Red")
class RedStick implements Stick {}

AnnotationUseStyle

Annotations should only use brackets and named attributes when they are needed. If only the default parameter is specified, then only the attribute value should be given. If there are no parameters, then no brackets should be given.

Valid:

@Entity
@Table("names")
@MyAnnotation(realm = "external")

Invalid:

@Entity()
@Table(value = "names")

AnonInnerLength

Anonymous inner classes should be no more than 20 lines.

ArrayTypeStyle

Enforces Java style arrays.

Valid:

public static void main(String[] args) {}

Invalid:

public static void main(String args[]) {}

AtclauseOrder

Javadoc @ clauses must be in the order:

/**
 *
 * @param ...
 * @author ...
 * @version ...
 * @serial ...
 * @return ...
 * @throws ...
 * @exception ...
 * @serialData ...
 * @serialField ...
 * @see ...
 * @since ...
 * @deprecated ...
 */

AvoidDoubleBraceInitialization

Detects double brace initialization.

Rationale: Double brace initialization (set of Instance Initializers in class body) may look cool, but it is considered as anti-pattern and should be avoided. This is also can lead to a hard-to-detect memory leak, if the anonymous class instance is returned outside and other object(s) hold reference to it. Created anonymous class is not static, it holds an implicit reference to the outer class instance. See this blog post and article for more details. Check ignores any comments and semicolons in class body.

Invalid:

class MyClass {
    List<Integer> list1 = new ArrayList<>() { // violation
        {
            add(1);
        }
    };
    List<String> list2 = new ArrayList<>() { // violation
        ;
        // comments and semicolons are ignored
        {
            add("foo");
        }
    };
}

AvoidEscapedUnicodeCharacters

Prevents use of obscure escape codes (e.g. \u221e). However, non-printable/control characters are still permitted.

Valid:

String unitAbbrev = "??s";
String byteOrdered = '\ufeff' = content;

Invalid:

String unitAbbrev = "\u03bcs";

AvoidInlineConditionals

Prevents use of the ?: operators.

AvoidNestedBlocks

Avoid unnecessary blocks.

Valid:

if (isDebug()) {
    // ...
}

Invalid:

// if (isDebug())
{
    // ...
}

AvoidNoArgumentSuperConstructorCall

Checks if call to superclass constructor without arguments is present. Such invocation is redundant because constructor body implicitly begins with a superclass constructor invocation super(); See specification for detailed information.

Valid:

class MyClass extends SomeOtherClass {
    MyClass(int arg) {
        super(arg); // OK, call with argument have to be explicit
    }
    MyClass(long arg) {
        // OK, call is implicit
    }
}

Invalid:

class MyClass extends SomeOtherClass {
    MyClass() {
        super(); // violation
    }
}

BooleanExpressionComplexity

Restrict the number of number of &&, ||, &, | and ^ in an expression to 2.

Valid:

if (a || (b && c)) {}

Invalid:

if (a > b || b > c || c == a || d > a) {}

CatchParameterName

Checks that catch parameter names conform to the following characteristic:

• allows names beginning with two lowercase letters followed by at least one uppercase or lowercase letter
• allows e abbreviation (suitable for exceptions end errors)
• allows ex abbreviation (suitable for exceptions)
• allows t abbreviation (suitable for throwables)
• prohibits numbered abbreviations like e1 or t2
• prohibits one letter prefixes like pException
• prohibits two letter abbreviations like ie or ee
• prohibits any other characters than letters

Valid:

catch(Exception txD) {}
catch(Exception txf) {}
catch(Exception e) {}
catch(Error e) {}
catch(Exception ex) {}
catch(Throwable t) {}

Invalid:

catch(Exception e2) {}
catch(Exception pExceptions) {}
catch(Exception gh) {}
catch(Exception e_x) {}

ClassDataAbstractionCoupling

Restricts to 7 the number of different classes instantiated within a class when that class is instantiated.

Valid:

class Valid {
    private final Item i1 = new Item();
    private final Item i2 = new Item();
    private final Item i3 = new Item();
    private final Item i4 = new Item();
    private final Item i5 = new Item();
    private final Item i6 = new Item();
    private final Item i7 = new Item();
    private final Item i8 = new Item();
}

Invalid:

class Invalid {
    private final ItemA i1 = new ItemA();
    private final ItemB i2 = new ItemB();
    private final ItemC i3 = new ItemC();
    private final ItemD i4 = new ItemD();
    private final ItemE i5 = new ItemE();
    private final ItemF i6 = new ItemF();
    private final ItemG i7 = new ItemG();
    private final ItemH i8 = new ItemH();
}

ClassFanOutComplexity

Restricts the number of other classes that a class can rely on to 20.

While ClassDataAbstractionCoupling limits the number of classes that are instantiated when the class is, this check counts all fields whether they are assigned a value or not.

ClassTypeParameterName

Restricts class generics parameters to be a single uppercase letter.

Valid:

class Deliverator <A> {}

Invalid:

class Invalidator <a> {}
class Invalidator <BB> {}
class Invalidator <C3> {}

CommentsIndentation

Requires the indentation of comments to match the surrounding code.

Valid:

/**
 * This is okay.
 */
int size = 20;

public foo() {
    super();
    // this is okay
}

public void foo11() {
    CheckUtils
        .getFirstNode(new DetailAST())
        .getFirstChild()
        .getNextSibling();
    // this is okay
}

Invalid:

    /**
     * This is NOT okay.
     */
int size = 20;

public foo() {
    super();
        // this is NOT okay
// this is NOT okay
}

public void foo11() {
    CheckUtils
        .getFirstNode(new DetailAST())
        .getFirstChild()
        .getNextSibling();
            // this is NOT okay
}

ConstantName

This check cannot be suppressed.

Requires constants (static, final fields) to be all uppercase. Numbers and numbers are permitted but not as the first character.

Valid:

private static final int JACK_CARD = 11;

Invalid:

private static final int ace_card = 1;
private static final int 12_CARD = 12;

CovariantEquals

This check cannot be suppressed.

Checks that classes which define a covariant equals() method also override method equals(Object).

Valid:

class Test {
    public boolean equals(Test i) {
        return false;
    }

    public boolean equals(Object i) {
       return false;
    }
}

Invalid:

class Test {
    public boolean equals(Test i) {
        return false;
    }
}

CyclomaticComplexity

Restricts the cyclomatic complexity of a method to 5. The cyclomatic complexity is a measure of the number of decision points in a method.

A method with no branches has a complexity of 1. For each if, while, do, for, ?:, catch, switch, case, && and || the complexity goes up by 1.

Valid:

void isValid(int a, int b, int c) {
    // 1
    if (a > b) { // +1 = 2
        switch (c) { // +1 = 3
            case 1: // +1 = 4
                break;
            case 2: // +1 = 5
                break;
        }
    }
}

Invalid:

void isInvalid(int a, int b, int c) {
    // 1
    if (a > b) { // +1 = 2
        switch (c) { // +1 = 3
            case 1: // +1 = 4
                break;
            case 2: // +1 = 5
                break;
            case 3: // +1 = 6
                break;
        }
    }
}

DeclarationOrder

Ensure class elements appear in the correct order.

Valid:

class Valid {
    // static
    public static int a;
    protected static int b;
    static int c;
    private static int d;

    // instance
    public int e;
    protected int f;
    int g;
    private int h;

    // constructors
    Valid() {}

    // methods
    void foo() {}
}

Invalid:

class Invalid {
    protected static int b;
    public static int a;
    private static int d;

    public int e;
    static int c;
    protected int f;
    private int h;

    void foo() {}

    Valid() {}

    int g;
}

DefaultComesLast

Check that the default is after all the cases in a switch statement.

Valid:

switch (a) {
    case 1:
        break;
    case 2:
        break;
    default:
        break;
}

Invalid:

switch (a) {
    case 1:
        break;
    default:
        break;
    case 2:
        break;
}

DesignForExtension

Judicous use of @SuppressWarnings("designdorextension") is recommended for this check.

This check is primarily intended for use in library modules rather than applications.

Classes that are deemed by their designer to be 'designed for extension', must take steps to prevent a subclass from breaking the class's behaviour by overriding methods incorrectly. This can be done through a combination of:

• Defining 'hook' methods with empty implementations that subclasses override to add their own behaviour
• Marking methods that are non-private and non-static as abstract or final

See the official Checkstyle documentation for more details and Effective Java, 2nd Edition by Josh Bloch: Item 17: Design and document for inheritance or else prohibit it.

EmptyBlock

Checks for empty blocks.

Valid:

if (a >b) {
	doSomething();
}

Invalid:

if (a > b) {
}

EmptyCatchBlock

Checks that catch blocks are not empty, or are commented with the word expected or ignore.

Valid:

try {
    something();
} catch (Exception e) {
    // ignore
}

Invalid:

try {
    something();
} catch (Exception e) {
    // do nothing
}

EmptyForInitializerPad

Checks that there is no padding in an empty for loop initialiser.

Valid:

for (; i < j ; i++) {}

Invalid:

for ( ; i < j ; i++) {}

EmptyForIteratorPad

Checks that there is no padding in an empty for loop iterator.

Valid:

for (Iterator i = list.getIterator(); i.hasNext() ;) {}

Invalid:

for (Iterator i = list.getIterator(); i.hasNext() ; ) {}

EmptyStatement

Checks for empty statements. An empty statement is a standalone semicolon (;).

Valid:

doSomething();

Invalid:

doSomething();;

EqualsAvoidNull

Checks that string literals are on the left side in an equals() comparison.

Valid:

String nullString = null;
"value".equals(nullString);

Invalid:

String nullString = null;
nullString.equals("value");

EqualsHashCode

This check cannot be suppressed.

Checks that when a class overrides the equals() method, that it also overrides the hashCode() method.

ExecutableStatementCount

Limits the number of executable statements in a method to 30.

ExplicitInitialization

Checks that object fields are not being explicitly initialised to their already default value.

Does not check primitive field types.

Valid:

class Valid {

    private int foo = 0;

    private Object bar;
}

Invalid:

class Invalid {

    private Integer foo = 0;

    private Object bar = null;
}

FallThrough

Checks that when a case in a switch statement falls through (i.e. doesn't end with break;) that the fall through is documented with a comment.

Valid:

switch (i) {
    case 0:
        i++; // fall through

    case 1:
        i++;
        // falls through

    case 2:
    case 3:
    case 4: { i++ } // fallthrough
    case 5:
        i++;
        /* fallthrou */
    case 6:
        i++;
        break;
}

Invalid:

switch (i) {
    case 0:
        i++;
    case 1:
        i++;
    case 2:
    case 3:
    case 4: { i++ }
    case 5:
        i++;
    case 6:
        i++;
        break;
}

FileLength

Checks that each file has no more than 2000 lines.

FileTabCharacter

Checks that there are no tab characters in the source files.

FinalClass

Checks that classes which have only private constructors are also declared as final. These classes can't be extended by a subclass as they can't call super() from their constructors.

Valid:

final class Valid {

    private Valid() {}
}

Invalid:

class Invalid {

    private Invalid() {}
}

FinalParameters

Parameters to a method must be final.

Valid:

void foo(final int a) {}

Invalid:

void foo(int a) {}

GenericWhitespace

Checks that the angle brackets around Generics parameters have the correct whitespace padding:

Valid:

public void <K, V extends Number> boolean foo(K, V) {}
class name<T1, T2, ..., Tn> {}
OrderedPair<String, Box<Integer>> p;
boolean same = Util.<Integer, String>compare(p1, p2);
Pair<Integer, String> p1 = new Pair<>(1, "apple");
List<T> list = ImmutableList.Builder<T>::new;
sort(list, Comparable::<String>compareTo);

HiddenField

Checks that a local variable or parameter in a method doesn't have the same name as a field. Doesn't apply in constructors or setters.

Valid:

class Foo {

    private int a;

    Foo(int a) {
        this.a = a;
    }

    setA(int a) {
        this.a = a;
    }
}

Invalid:

class Bar {

    private int b;

    void baz(int b) {
        // ...
    }
}

HideUtilityClassConstructor

Classes that only have static fields or methods should not have a public constructor. This includes the default constructor.

Valid:

final class StringUtils {

    private Utils() {}

    private static int count(chat c, String s) {}
}

class StringUtils {

    protected Utils() {
        throw new UnsupportedOperationException();
    }

    private static int count(chat c, String s) {}
}

Invalid:

class StringUtils {

    private static int count(chat c, String s) {}
}

IllegalCatch

Prevent the following types from being in a catch statement:

• java.lang.Exception
• java.lang.Throwable
• java.lang.RuntimeException

Valid:

try {
    doSomething();
} catch (SpecificException e) {
    // log
}

Invalid:

try {
    doSomething();
} catch (Exception e) {
    // log
}

IllegalImport

Prevent importing from the sun.* packages.

Invalid:

import sun.security.provider.Sun;

IllegalThrows

Prevent the following types from being thrown:

• java.lang.Exception
• java.lang.Throwable
• java.lang.RuntimeException

Valid:

throw new SpecificException("error");

Invalid:

throw new RuntimeException("boom!");

IllegalToken

Checks that labels are not used.

IllegalType

Prevents use of implementation classes as variables, parameters or method returns. Use the interfaces instead.

Prevents variables, parameters and method returns from being any of the following:

• java.util.ArrayDeque
• java.util.ArrayList
• java.util.EnumMap
• java.util.EnumSet
• java.util.HashMap
• java.util.HashSet
• java.util.IdentityHashMap
• java.util.LinkedHashMap
• java.util.LinkedHashSet
• java.util.LinkedList
• java.util.PriorityQueue
• java.util.TreeMap
• java.util.TreeSet

Valid:

Set<String> getNames();

Invalid:

HashSet<String> getNames();

InnerAssignment

Checks for assignments within an expressions. However, it still allows assignment in a while loop clause.

Valid:

while((line = reader.readLine()) != null) {
}

Invalid:

String s = Integer.toString(i = 2);

InnerTypeLast

Inner classes must appear at the bottom of a class, below fields and methods.

InterfaceIsType

An interface must define methods, not just constants.

Valid:

interface Foo {

    static final String "Foo!!";

    getBar();
}

Invalid:

interface Foo {

    static final String "Foo!!";
}

InterfaceTypeParameterName

Checks that the type parameters for an interface are a single uppercase letter.

Valid:

interface <T> Portable {}

Invalid:

interface <Type> Portable {}

JavadocMissingLeadingAsterisk

Checks if the javadoc has leading asterisks on each line.

The check does not require asterisks on the first line, nor on the last line if it is blank. All other lines in a Javadoc should start with *, including blank lines and code blocks.

Valid:

/**
 * Valid Java-style comment.
 *
 * <pre>
 *   int value = 0;
 * </pre>
 */
class JavaStyle {} // ok

/** Valid Scala-style comment.
  * Some description here.
  **/
class ScalaStyle {} // ok

/** **
  * Asterisks on first and last lines are optional.
  * */
class Asterisks {} // ok

/** No asterisks are required for single-line comments. */
class SingleLine {} // ok

Invalid:

/** // violation on next blank line, javadoc has lines without leading asterisk.

 */
class BlankLine {}

/** Wrapped
    single-line comment */ // violation, javadoc has lines without leading asterisk.
class Wrapped {}

/**
  * <pre>
    int value; // violation, javadoc has lines without leading asterisk.
  * </pre>
  */
class Code {}

JavadocMissingWhitespaceAfterAsterisk

Checks that there is at least one whitespace after the leading asterisk. Although spaces after asterisks are optional in the Javadoc comments, their absence makes the documentation difficult to read. It is the de facto standard to put at least one whitespace after the leading asterisk.

Valid:

/** This is valid single-line Javadoc. */
class TestClass {
  /**
   * This is valid Javadoc.
   */
  void validJavaDocMethod() {
  }
  /** This is valid single-line Javadoc. */
  void validSingleLineJavaDocMethod() {
  }
}

Invalid:

class TestClass {
  /**
   *This is invalid Javadoc.
   */
  int invalidJavaDoc;
  /**This is invalid single-line Javadoc. */
  void invalidSingleLineJavaDocMethod() {
  }
}

JavadocPackage

Checks that each package has a package-info.java file.

JavadocParagraph

Checks that paragraphs in Javadoc blocks are wrapped in <p> elements and have blank lines between paragraphs. This first paragraph does not need the <p> elements.

JavadocStyle

Checks the formatting of the Javadoc blocks. See the official Checkstyle documentation for all the checks that are applied.

JavadocType

Checks the format for Javadoc for classes and enums. Javadoc must be present, not have any unknown tags and not missing any @param tags.

JavaNCSS

Restricts the NCSS score for methods, classes and files to 40, 1200 and 1600 respectively. The NCSS score is a measure of the number of statements within a scope.

Too high an NCSS score suggests that the method or class is doing too much and should be decomposed into smaller units.

LambdaBodyLength

Checks lambda body length.

Rationale: Similar to anonymous inner classes, if lambda body becomes very long it is hard to understand and to see the flow of the method where the lambda is defined. Therefore, long lambda body should usually be extracted to method.

Valid:

Runnable r3 = () -> { // ok, 10 lines
    System.out.println(2); // line 2 of lambda
    System.out.println(3);
    System.out.println(4);
    System.out.println(5);
    System.out.println(6);
    System.out.println(7);
    System.out.println(8);
    System.out.println(9);
}; // line 10

Invalid:

Runnable r = () -> { // violation, 11 lines
    System.out.println(2); // line 2 of lambda
    System.out.println(3);
    System.out.println(4);
    System.out.println(5);
    System.out.println(6);
    System.out.println(7);
    System.out.println(8);
    System.out.println(9);
    System.out.println(10);
}; // line 11

Runnable r2 = () -> // violation, 11 lines
  "someString".concat("1") // line 1 of lambda
              .concat("2")
              .concat("3")
              .concat("4")
              .concat("5")
              .concat("6")
              .concat("7")
              .concat("8")
              .concat("9")
              .concat("10")
              .concat("11"); // line 11

LambdaParameterName

Checks the format of lambda parameter names.

Identifiers must match ^[a-z][a-zA-Z0-9]*$.

LeftCurly

Checks that the left curly brace ('{') is placed at the end of the line. Does not check enums.

Valid:

class Foo {
}

Invalid:

class Bar
{

}

LineLength

Limits the line length to 120 characters.

Doesn't check package or import lines.

LocalFinalVariableName

Checks the format of local, final variable names, including catch parameters.

Identifiers must match ^[a-z][a-zA-Z0-9]*$.

LocalVariableName

Checks the format of local, non-final variable names.

Identifiers must match ^[a-z][a-zA-Z0-9]*$.

MagicNumber

Checks that numeric literals are defined as constants. Being constants they then have a name that aids in making them non-magical.

The numbers -1, 0, 1 and 2 are not considered to be magical.

Valid:

static final int SECONDS_PER_DAY = 24 * 60 * 60;
static final Border STANDARD_BORDER = BorderFactory.createEmptyBorder(3, 3, 3, 3);

Invalid

String item = getItem(200);

MemberName

Checks the format of non-static field names.

Identifiers must match ^[a-z][a-zA-Z0-9]*$.

MethodCount

Restricts the number of methods in a type to 30.

MethodLength

Restricts the number of lines in a method to 60. Include blank lines and single line comments. You should be able to see an entire method without needing to scroll.

MethodName

Checks the format of method names.

Identifiers must match ^[a-z][a-zA-Z0-9]*$.

MethodParamPad

Checks that the padding between the method identifier and the left parenthesis is on the same line and doesn't have a space in-between.

Valid:

void getInstance();

Invalid:

void getInstance ();

void getValue
    ();

MethodTypeParameterName

Restricts method generics parameters to be a single uppercase letter.

Valid:

List<A> getItems() {}

Invalid:

List<a> getItems() {}
List<BB> getItems() {}
List<C3> getItems() {}

MissingDeprecated

Both the @Deprecated annotation and the Javadoc tag @deprecated must be used in pairs.

Valid:

/**
  * Foo.
  *
  * @deprecated
  */
@Deprecated
void foo() {}

Invalid:

/**
  * Foo.
  */
@Deprecated
void foo() {}

/**
  * Bar.
  *
  * @deprecated
  */
void bar() {}

MissingSwitchDefault

Checks that switch statement has a default case.

Valid:

switch (foo) {
    case 1:
        //
        break;
    case 2:
        //
        break;
    default:
        throw new IllegalStateExcetion("Foo: " + foo);
}

Invalid:

switch (foo) {
    case 1:
        //
        break;
    case 2:
        //
        break;
}

ModifiedControlVariable

Checks that the control variable in a for loop is not modified inside the loop.

Invalid:

for (int i = 0; i < 1; i++) {
    i++;
}

ModifierOrder

Check that modifiers are in the following order:

• public
• protected
• private
• abstract
• static
• final
• transient
• volatile
• synchronized
• native
• strictfp

Type annotations are ignored.

MultipleStringLiterals

Checks for multiple occurrences of the same string literal within a single file. Does not apply to empty strings ("").

Invalid:

String fooFoo = "foo" + "foo";

MultipleVariableDeclarations

Checks that each variable is declared in its own statement and line.

Valid:

int a;
int b;

Invalid:

int a, b;

MutableException

Checks that Exception classes are immutable. However, you can still call setStackTrace.

Classes checked are those whose name ends with the following. Or that the class they extend does.

• Exception
• Error
• Throwable

NeedBraces

Check that code blocks are surrounded by braces.

Valid:

if (obj.isValid()) {
    return true;
}

while (obj.isValid()) {
    return true;
}

do {
    this.notify();
} while (o != null);

for (int i = 0; ;) {
    this.notify();
}

Invalid:

if (obj.isValid()) return true;

while (obj.isValid()) return true;

do this.notify(); while (o != null);

for (int i = 0; ;) this.notify();

NestedForDepth

Checks that for loops are not nested more than 1 deep.

Valid:

for (int i = 0; i < 1; i++) { // depth 0
    for (int j = 0; j < 1; j++) { // depth 1
        //
    }
}

Invalid:

for (int i = 0; i < 1; i++) { // depth 0
    for (int j = 0; j < 1; j++) { // depth 1
        for (int k = 0; j < 1; k++) { // depth 2!
            //
        }
    }
}

NestedIfDepth

Checks that if blocks are not nested more than 1 deep.

Valid:

if (isValid()) { // depth 0
    if (isExpected()) { // depth 1
        doIt();
    }
}

Invalid:

if (isValid()) { // depth 0
    if (isExpected()) { // depth 1
        if (isNecessary()) { // depth 2!
            doIt();
        }
    }
}

NestedTryDepth

Checks that try blocks are not nested.

Valid:

try {
    doSomething();
    doSomeOtherThing();
} catch (SomeException se) {
    // handle it
} catch (OtherExceptions oe) {
    // handle it
}

Invalid:

try {
   doSomething();
   try {
       doSomeOtherThing();
   } catch (OtherExceptions oe) {
       // handle it
   }
} catch (SomeException se) {
   // handle it
}

NewlineAtEndOfFile

Checks that files end with a line-feed character, (i.e. unix-style line ending).

NoClone

This check cannot be suppressed.

Checks that the clone() method from Object has not been overridden. Use a copy constructor, or better yet, a static factory method.

See Effective Java, 2nd Edition by Josh Bloch: Item 11: Override clone judiciously.

NoCodeInFile

Checks whether file contains code. Files which are considered to have no code:

• File with no text
• File with only single line comment(s)
• File with only a multi line comment(s).

Invalid:

// single line comment // violation

Invalid:

/* // violation
 block comment
*/

NoFinalizer

Checks that the finalize() method from Object has not been overridden.

See Effective Java, 2nd Edition by Josh Bloch: Item 7: Avoid finalizers.

NoLineWrap

Prevents wrapping of package and import statements.

NonEmptyAtclauseDescription

Checks that the Javadoc clauses @param, @return, @throws and @deprecated all have descriptions.

Valid:

/**
 * Foo.
 *
 * @returns the foo
 */

Invalid:

/**
 * Foo.
 *
 * @returns
 */

NoWhitespaceAfter

Checks that there is no whitespace after the array init ('{'), prefix increment ('++'), prefix decrement ('--'), bitwise complement ('~'), logical complement ('!'), array declaration ('[' in int[] a;) or array index operator ('[' in a[2]).

Valid:

int[] y = {1, 2};
++i;
--i;
int j = -1;
int k = +1;
int l = ~2;
boolean state = !isReady();
int b = o.getValue();
int[] a;
int d = a[2];

Invalid:

int[] y = { 1, 2 };
++ i;
-- i;
int j = - 1;
int k = + 1;
int l = ~ 2;
boolean state = ! isReady();
int b = o. getValue();
int[ ] a;
int d = a[ 2];

NoWhitespaceBefore

Checks that there is no whitespace before the comma operator (','), statement terminator (';'), postfix increment ('++') or postfix decrement ('--').

Valid:

int y = {1, 2};
doSomething();
i++;
i--;

Invalid:

int y = {1 , 2};
doSomething() ;
i ++;
i --;

NoWhitespaceBeforeCaseDefaultColon

Checks that there is no whitespace before the colon in a switch block. .

Valid:

switch(1) {
    case 1:
        break;
    case 2:
        break;
    default:
        break;
}

Invalid:

switch(2) {
    case 2: // ok
        break;
    case 3, 4
             : break; // violation, whitespace before ':' is not allowed here
    case 4,
          5: break; // ok
    default
          : // violation, whitespace before ':' is not allowed here
        break;
}

NPathComplexity

Checks that the NPATH score (number of paths) through a method is no more than 5. This is similar to Cyclomatic Complexity.

OneStatementPerLine

Checks that there is only one statement per line.

Valid:

doSomething();
doSomethingElse();

Invalid:

doSomething(); doSomethingElse();

OneTopLevelClass

This check cannot be suppressed.

Checks that each source file contains only one top-level class, interface or enum.

OperatorWrap

Checks that when wrapping a line on an operator that the operator appears on the new line.

Valid:

int answer = getTheAnswerToLife() + getTheAnswerToTheUniverse()
    + getTheAnswerToEverything();

Invalid:

int answer = getTheAnswerToLife() + getTheAnswerToTheUniverse() +
    getTheAnswerToEverything();

OuterTypeFilename

This check cannot be suppressed.

Checks that the source filename matches the name of the top-level class. e.g. class Foo {} is in file Foo.java.

OverloadMethodsDeclarationOrder

Checks that overload methods are grouped together in the source file.

PackageAnnotation

Checks that package level annotations are in the package-info.java file.

PackageDeclaration

This check cannot be suppressed.

Checks that the class has a package definition.

PackageName

Checks the format of package names. Only lowercase letters, no initial numbers or any underscores.

Identifiers must match ^[a-z]+(\.[a-z][a-z0-9]+)*$.

ParameterName

Checks the format of method parameter names, including catch parameters.

Identifiers must match ^[a-z][a-zA-Z0-9]*$.

ParameterNumber

Restricts the number of parameters in a method or constructor to 7. Overridden methods are not checked as there may be no access to change the super method.

ParenPad

Checks that there are no spaces padding parentheses.

Valid:

doSomething();
doSomethingElse(5);

Invalid:

doSomething( );
doSomethingElse( 5);
doSomethingElse(5 );

RegexpOnFilename

Checks for the existence of forbidden java file names.

File names are forbidden if they match the pattern (.sync-conflict-| conflicted copy ).

N.B. only *.java files are checked.

This check is intended to detect Syncthing and Dropbox conflict files.

e.g.

DataClass (Bob's conflicted copy 2017-03-11).java
DataClass.sync-conflict-20170311-1648.java

RequireThis

Checks that references to instance fields where a parameter name overlaps are qualified by this..

ReturnCount

Restricts methods to have at most 2 return statements in non-void methods, and at most 1 in void methods.

Valid:

int getNumber(int a) {
    if (a > 1) {
        return a;
    }
    return 0;
}

void getName(int a) {
    String name = "default";
    if (a > 1) {
        name = "Bob";
    }
    return name;
}

Invalid:

int getNumber(int a) {
    if (a > 1) {
        return a;
    }
    if (a < 2) {
        return a * a;
    }
    return 0;
}

void getName(int a) {
    if (a > 1) {
        return "Bob";
    }
    return "default";
}

RightCurly

Checks that the right curly brace ('}') is placed on the same line as the next part of a multi-block statement (e.g. try-catch-finally, if-then-else).

Valid:

try {
    //
} catch (Exception e) {
    //
} finally {
    //
}

if (a > 0) {
    //
} else {
    //
}

Invalid:

try {
    //
}
catch (Exception e) {
    //
}
finally {
    //
}

if (a > 0) {
    //
}
else {
    //
}

if (a > 0) {
    //
} a = 2;

public long getId() {return id;}

SeparatorWrap

Checks the line wrapping around separators.

• The comma separator (',') should be at the end of the line.
• The dot separator ('.') should be on the new line.

Valid:

doSomething(alpha, beta,
    gamma);
doSomethingElse().stream()
                 .forEach(System.out::println);

Invalid:

doSomething(alpha, beta
    , gamma);
doSomethingElse().stream().
                  forEach(System.out::println);

SimplifyBooleanExpression

Checks for overly complicated boolean expressions. Checks for code like b == true, b || true, !false, etc.

Valid:

if (b) {}
if (true) {}

Invalid:

if (b == true) {}
if (b || true) {}
if (!false) {}

SimplifyBooleanReturn

Checks for overly complicated boolean return statements.

Valid:

return !valid();

Invalid:

if (valid()) {
    return false;
} else {
    return true;
}

SingleSpaceSeparator

Checks that non-whitespace characters on the same line are separated by no more than one whitespace.

Valid:

if (a < 0) {}
public long toNanos(long d) { return d; };

Invalid:

if  (a < 0) {}
public long toNanos(long d)  { return d;             };

StaticVariableName

Checks the format of static, non-final variable names.

Identifiers must match ^[a-z][a-zA-Z0-9]*$.

StringLiteralEquality

Checks that string literals are not used with == or !=.

Valid:

if ("something".equals(x)) {}

Invalid:

if (x == "something") {}

SuppressWarnings

Prevents the use of @SuppressWarnings for the following checks:

• ConstantName
• CovariantEquals
• EqualsHashCode
• NoClone
• OneTopLevelClass
• OuterTypeFilename
• PackageDeclaration
• TypeName
• VisibilityModifier

SuppressWarningsFilter

Allows the use of the @SuppressWarnings annotation.

SuppressWarningsHolder

Used by Checkstyle to hold the checks to be suppressed from @SuppressWarnings(...) annotations.

ThrowsCount

Restricts non-private methods to only throws 4 distinct Exception types. Exceptions should be hierarchical to allow catching suitable root Exceptions.

See Effective Java, 2nd Edition, Chapter 9: Exceptions

Valid:

void doSomething() throws IllegalStateException, DowsingServiceException,
    BalancedBudgetException, ManagementInterferanceException {}

Invalid:

void doSomething() throws IllegalStateException,
    DowsingNotPermittedException, DowsingServiceNotReadyException,
    BalancedBudgetException, ManagementInterferanceException {}

TodoComment

Checks for remaining TODO and FIXME comments left in code. Their presence indicates that the program isn't finished yet.

TrailingComment

Checks for comments at the end of lines.

Valid:

// comment on line by itself
    // comment after white space
if (a < 1) {
    //
} // comment on closing brace
int[] a = new int[2](
    1, 2
); // comment on closing parenthesis of statement

Invalid:

int a = 1; // comment in line with statement
if (a < 1) { // comment on line with if statement
    //
}
int[] a = new int[2](
    1, // first value - invalid comment
    2  // second value - also invalid comment
);

Translation

Checks that all messages*.properties files all have the same set of keys.

TypecastParenPad

Checks that there are no spaces within the typecasting parentheses.

Valid:

String s = (String) list.get(2);

Invalid:

String s = (String ) list.get(2);
String s = ( String) list.get(2);
String s = ( String ) list.get(2);

TypeName

This check cannot be suppressed.

Checks the format of class, interface, enum identifiers, including annotations.

Identifiers must match ^[A-Z][a-zA-Z0-9]*$.

UncommentedMain

Checks for public static void main() methods that may have been left over from testing. Allowed in classes whose names end in Main or Application.

UniqueProperties

Checks *.properties files for duplicate property keys.

UnnecessaryParentheses

Checks for the use of unnecessary parentheses.

Valid:

if (a < 1) {}

Invalid:

if ((a < 1)) {}

UnnecessarySemicolonAfterOuterTypeDeclaration

Checks if unnecessary semicolon is used after type declaration.

Valid:

class A {

   class Nested {

   }; // OK, nested type declarations are ignored

}

interface B {

}

enum C {

}

@interface D {

}

Invalid:

class A {

   class Nested {

   }; // OK, nested type declarations are ignored

}; // violation

interface B {

}; // violation

enum C {

}; // violation

@interface D {

}; // violation

UnusedImports

Checks for unused imports. Does not inspect wildcard imports, which should be blocked by AvoidStarImport anyway.

Imports are unused if:

• They are not referenced in the file.
• It duplicates another import.
• It import from the java.lang package.
• It imports a class from the same package.
• It is only references from the Javadoc.

UpperEll

Checks that long numeric literal values are marked by an upper-case ell ('L'). The lower-case ell ('l') can be mistaken for the numeral one ('1').

Valid:

long id = 12345L;

Invalid:

long id = 12345l;

VariableDeclarationUsageDistance

Checks that a variable declaration and its first usage are not more than 3 lines. Blocks of initialisation methods don't count toward this total.

See the official Checkstyle documentation for examples.

VisibilityModifier

This check cannot be suppressed.

Checks the visibility of class members to help enforce encapsulation. Only static final fields, immutable (see list below) fields or field with special annotation (see list below), may be public.

The following are considered immutable when final, and can be public:

• java.lang.String
• java.lang.Integer
• java.lang.Byte
• java.lang.Character
• java.lang.Short
• java.lang.Boolean
• java.lang.Long
• java.lang.Double
• java.lang.Float
• java.lang.StackTraceElement
• java.math.BigInteger
• java.math.BigDecimal
• java.io.File
• java.util.Locale
• java.util.UUID
• java.net.URL
• java.net.URI
• java.net.Inet4Address
• java.net.Inet6Address
• java.net.InetSocketAddress

Fields with the following annotations may be public:

• org.junit.Rule
• org.junit.ClassRule
• com.google.common.annotations.VisibleForTesting

Valid:

class Foo {

    public final Long id;

    public final String name;

    private String description;

    @VisibleForTesting
    public State state;

    Foo(final Long id, final String name) {
        this.id = id;
        this.name = name;
    }
}

Invalid:

class Foo {

    public Long id;

    public String name;

    private String description;

    public State state;

    Foo(final Long id, final String name) {
        this.id = id;
        this.name = name;
    }
}

WhitespaceAfter

Checks that commas (','), statement terminators (';') and typecasts are all followed by a space.

Valid:

doSomething(1, 2, 3);
if (a > 1) { return true; }
String name = (String) list.get(9);

Inalid:

doSomething(1,2,3);
if (a > 1) { return true;}
String name = (String)list.get(9);

WhitespaceAround

Checks that tokens are surrounded by whitespace.

Sevntu

Disabled Checks

These checks are not enabled. Notes are included for each explaining why.

Checkstyle

AbstractClassName

Prevents some more meaningful abstract class names

ArrayTrailingComma

Couldn't get my IDE's (IntelliJ) code style to match.

AvoidStarImport

Ref: Clean Code, Robert C. Martin, J1: Avoid Long Import Lists by Using Wildcards

AvoidStaticImport

Ref: Clean Code, Robert C. Martin, J2: Don't Inherit Constants Recommends using a static import to access constants from another class over inheriting them.

EmptyLineSeparator

FinalLocalVariable

Doesn't recognise Lombok's val as being final.

Header

Shouldn't need to list in every file, simply listing in project root should be enough.

IllegalInstantiation

Not really suitable for a template ruleset as it requires an explicit list of classes to apply to.

IllegalTokenText

Generic rule; doesn't embody a 'quality' check.

ImportControl

Generic rule; doesn't embody a 'quality' check.

ImportOrder

Generic rule; doesn't embody a 'quality' check.

Indentation

Couldn't get my IDE's (IntelliJ) code style to match.

InterfaceMemberImpliedModifier

Makes interfaces overly verbose.

JavadocMethod

Only exceptional cases should need to be documented.

JavadocTagContinuationIndentation

Couldn't get my IDE's (IntelliJ) code style to match.

JavadocVariable

Member variables should usually be named such that it is clear what they are. Comments for clarification should be the exception.

MissingCtor

Would not see constructors created using Lombok's @NoArgsConstructor.

MissingOverride

The javadoc compiler automatically inherits the javadoc from the overridden method, it doesn't need to be told to do so.

OuterTypeNumber

Already covered by the OneTopLevelClass check.

ParameterAssignment

FinalParameters already protects against assigning values to parameters.

RedundantImport

UnusedImports performs all the same checks and more.

RedundantModifier

conflicts with InterfaceMemberImpliedModifier which is now prefered given changes to interfaces in Java 9

Regexp

Generic rule; doesn't embody a 'quality' check.

RegexpHeader

Generic rule; doesn't embody a 'quality' check.

RegexpMultiline

Generic rule; doesn't embody a 'quality' check.

RegexpOnFilename

Generic rule; doesn't embody a 'quality' check.

RegexpSingleline

Generic rule; doesn't embody a 'quality' check.

RegexpSinglelineJava

Generic rule; doesn't embody a 'quality' check.

SingleLineJavadoc

I don't use single line javadoc blocks.

SummaryJavadoc

Generic rule; doesn't embody a 'quality' check.

SuperClone

Overridding the clone() method is not allowed by the NoClone check.

SuperFinalize

NoFinalizer prevents use of finalize().

WriteTag

Generic rule; doesn't embody a 'quality' check.

Sevntu

As the sevntu check are considered experimental not all those that are not enabled are listed here. Only where they are disabled due to a conflict with my 'style' or there is another irreconcilable difference that prevents them from being enabled, will they be documented to prevent repeated investigations.

AvoidConditionInversion

Should already be covered by SimplifyBooleanExpression.

AvoidConstantAsFirstOperandInCondition

Checks that condition expressions don't become less readable by attempting to use a constant on the left-hand-side of a comparison.

Valid:

if (a == 12) {}

Invalid:

if (12 == a) {}

AvoidDefaultSerializableInInnerClasses

Prevent the use of default serialization methods on inner classes. If an inner class needs to implement the Serializable interface, then it must implement both writeObject() and readObject() methods.

AvoidHidingCauseException

Ensures that an exception is re-thrown properly and is not swallowed by a catch block.

Valid:

try {
    doSomething();
} catch (MyException e) {
    throw new MyOtherException(e);
}

Invalid:

try {
    doSomething();
} catch (MyException e) {
    throw new MyOtherException();
}

AvoidModifiersForTypes

Generic rule; doesn't embody a 'quality' check.

AvoidNotShortCircuitOperatorsForBoolean

Prevents the use of boolean operators that don't allow short-circuiting the expression. (e.g. '|', '&', '|=' and '&=')

Valid:

if ((a < b) || (b > getExpensiveValue())) {}

Invalid:

if ((a < b) | (b > getExpensiveValue())) {}

CauseParameterInException

Should already be covered by AvoidHidingCauseException.

ChildBlockLength

Appears to be broken as of 1.21.0.

ConfusingCondition

Checks that the expression with the if condition in an if-then-else statement is not negated.

Valid:

if (isValid()) {
    handleValidCondition();
} else {
    handleInvalidCondition();
}

Invalid:

if (!isValid()) {
    handleInvalidCondition();
} else {
    handleValidCondition();
}

ConstructorWithoutParams

Exception class constructors must accept parameters for message and/or cause. This check is applied to classes whose name ends with Exception.

CustomDeclarationOrder

The DeclarationOrder check already imposes an order for class elements.

DiamondOperatorForVariableDefinition

Checks that the diamond operator is used where possible.

Valid:

Map<Long, String> idTable = new HashMap<>();

Invalid:

Map<Long, String> idTable = new HashMap<Long, String>();

EitherLogOrThrow

Checks that when an exception is caught, that if it is logged then it is not also re-thrown. Log or throw; one or the other or neither, but not both.

Accepts java.util.logging.Logger and org.slf4j.Logger.

EmptyPublicCtorInClass

This Check looks for useless empty public constructors. Class constructor is considered useless by this Check if and only if class has exactly one ctor, which is public, empty(one that has no statements) and default.

Valid:

class ValidPrivateCtor {
    private ValidPrivateCtor() {
    }
}

class ValidOverloadedCtor {
    public ValidOverloadedCtor() {
    }
    public ValidOverloadedCtor(int i) {
    }
}

Invalid:

class Invalid {
     public Invalid() {
     }
}

EnumValueName

Checks that Enum Values match the pattern: ^[A-Z][A-Z0-9]*(_[A-Z0-9]+)*$

Valid:

enum Valid {

    ALPHA, BETA, GAMMA_RAY;
}

Invalid:

enum InvalidConstants {

    alpha, Beta;
}

FinalizeImplementation

Checks that the finalize() implementation doesn't ignore the base class implementation, and doesn't only call the base class implementation.

Valid:

class Valid {
    protected void finalize() {
        try {
            doSomething();
        } finally {
            super.finalize();
        }
    }
}

Invalid:

class InvalidNoEffect1 {
    protected void finalize() {
    }
}
class InvalidNoEffect2 {
    protected void finalize() {
        doSomething();
    }
}
class InvalidUseless {
    protected void finalize() {
        super.finalize();
    }
}
class InvalidPublic {
    public void finalize() {
        try {
            doSomething();
        } finally {
            super.finalize();
        }
    }
}

ForbidAnnotation

Generic rule; doesn't embody a 'quality' check.

ForbidCCommentsInMethods

Prevents the use of /* C-style */ comments inside methods.

Valid:

void doSomething() {
    // a comment
}

Invalid:

void doSomething() {
    /* invalid */
}

ForbidCertainImports

Generic rule; doesn't embody a 'quality' check.

ForbidInstantiation

Generic rule; doesn't embody a 'quality' check.

ForbidReturnInFinallyBlock

Prevent the use of a return statement in the finally block.

Invalid:

try {
    doSomething();
{ catch (IOException e) {
    // log error
} finally (
    return true; // invalid
}

ForbidThrowAnonymousExceptions

IllegalThrows performs a similar check.

ForbidWildcardAsReturnType

Prevents declaring a method from returning a wildcard type as its return value.

Valid:

<E> List<E> getList() {}

Invalid:

<E> List<? extends E> getList() {}

LogicConditionNeedOptimization

Prevent the placement of variables or fields after methods in an expression.

Valid:

if (property && getProperty()) {}

Invalid:

if (getProperty() && property) {}

MapIterationInForEachLoop

Checks for unoptimised iterations over Maps. Check use of map.values(), map.keySet() and map.entrySet() against the use of the iterator produced to verify if another could be better.

MoveVariableInsideIfCheck

Checks if a variable is declared outside an if block that is only used within that block.

Valid:

if (condition) {
    String variable = input.substring(1);
    return method(variable);
}
return "";

Invalid:

String variable = input.substring(1);
if (condition) {
    return method(variable);
}
return "";

NameConventionForJunit4TestClasses

Checks the names of JUnit test classes. Classes checked are those that have at least one method annotated with Test or org.junit.Test.

Test class names must match: .+Test\\d*|.+Tests\\d*|Test.+|Tests.+|.+IT|.+ITs|.+TestCase\\d*|.+TestCases\\d*

NestedSwitch

Checks that switch statements are not nested within one another.

Valid:

void doSomething(int a, int b) {

    switch(a) {
        case 1:
            doMore(b);
            break;
        case 2:
            // ..
        }
    }
}

void doMore(int b) {

    switch(b) {
        case 1:
            //
        case 2:
            //
    }
}

Invalid:

void doSomething(int a, int b) {

    switch(a) {
        case 1:
            switch(b) {
                case 1:
                    //
                case 2:
                    //
            }
            break;
        case 2:
            // ..
        }
    }
}

NoMainMethodInAbstractClass

Prevents a main method from existing in an abstract class.

NumericLiteralNeedsUnderscore

Checks that numeric literals use underscores ('_') if over a certain length.

• Decimals

  • 7 or more digits must use the underscore
  • No more than 3 digits between underscores

• Hex

  • 5 or more digits must use the underscore
  • No more than 4 digits between underscores

• Binary

  • 9 or more digits must use the underscore
  • No more than 8 digits between underscores

OverridableMethodInConstructor

Prevents calls to overridable methods from constuctors including other methods that perform the same functions. (i.e. Cloneable.clone() and Serializable.readObject())

Invalid:

abstract class Base {
    Base() {
        overrideMe();
    }
}
class Child extends Base {
    final int x;
    Child(int x) {
        this.x = x;
    }
    void overrideMe() {
        System.out.println(x);
    }
}
new Child(42); // prints "0"

PublicReferenceToPrivateType

Checks that a type is not exposed outside its declared scope.

Invalid:

public class OuterClass {
    public InnerClass inner = new InnerClass();
    public SiblingClass sibling = new SiblingClass();
    public InnerClass getValue() { return new InnerClass(); }
    public SiblingClass getSibling() { return new SiblingClass(); }
    private class InnerClass {}
}
class SiblingClass {}

RedundantReturn

Checks for redundant return statements.

Invalid:

HelloWorld() {
    doStuff();
    return;
}
void doStuff() {
    doMoreStuff();
    return;
}

RequiredParameterForAnnotation

Generic rule; doesn't embody a 'quality' check.

ReturnBooleanFromTernary

Ternary statements shouldn't have Boolean values as results.

Valid:

Boolean set = isSet();
Boolean notReady = !isReady();

Invalid:

Boolean set = isSet() ? True : False;
Boolean notReady = isReady() ? False : True;

ReturnNullInsteadOfBoolean

The Boolean type is meant to only represent a binary state: TRUE or FALSE. It is not a ternary value: TRUE, FALSE, null.

Invalid:

Boolean isEnabled() {
    if (level > 0) {
        return True;
    }
    if (level < 0) {
        return False;
    }
    return null;
}

SimpleAccessorNameNotation

allow use of non-bean property-like naming

SingleBreakOrContinue

Checks that there is at most one continue or break statement within a looping block (e.g. for, while, ...)

StaticMethodCandidate

Can't handle private methods called by reflection, which may cause issues with Spring and other DI frameworks.

TernaryPerExpressionCount

Checks that there is at most one ternary statments (?:) within an expression.

Invalid:

String x = value != null ? "A" : "B" + value == null ? "C" : "D"

UniformEnumConstantName

Checks that all the values of an enum follow the same naming pattern.

Valid:

public enum EnumOne {
    FirstElement, SecondElement, ThirdElement;
}

public enum EnumTwo {
    FIRST_ELEMENT, SECOND_ELEMENT, THIRD_ELEMENT;
}

Invalid:

public enum EnumThree {
    FirstElement, SECOND_ELEMENT, ThirdElement;
}

UselessSingleCatch

Checks for catch blocks that are useless. i.e. that catch all exceptions and then just rethrow them.

Invalid:

try {
    doSomething();
} catch (Exception e) {
    throw e;
}

UselessSuperCtorCall

Checks for useless calls to the super() method in constructors.

Invalid:

class Dummy {
    Dummy() {
        super();
    }
}
class Derived extends Base {
    Derived() {
        super();
    }
}

WhitespaceBeforeArrayInitializer

This checks enforces whitespace before array initializer.

Valid:

int[] ints = new int[] {
    0, 1, 2, 3
};

int[] tab = new int[]
                {0, 1, 2, 3};

Invalid:

int[] ints = new int[]{0, 1, 2, 3};