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README.md

kemitix-checkstyle-ruleset

Provides an extensive Checkstyle ruleset for use with Apache's maven-checkstyle-plugin.

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

Requirements

Usage

To use this ruleset in your maven-checkstyle-plugin configuration add checkstyle, sevntu-checkstyle-maven-plugin and kemitix-checktyle-ruleset as dependencies of the maven-checkstyle-plugin.

You need to include checkstyle as the version bundled with the maven-checkstyle-plugin is not up-to-date enough.

<properties>
    <checkstyle.version>7.0</checkstyle.version>
    <sevntu-checkstyle-maven-plugin.version>1.21.0</sevntu-checkstyle-maven-plugin.version>
    <kemitix-checkstyle-ruleset.version>0.1.1</kemitix-checkstyle-ruleset.version>
</properties>
<pluginManagement>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-checkstyle-plugin</artifactId>
            <dependencies>
                <dependency>
                    <groupId>com.puppycrawl.tools</groupId>
                    <artifactId>checkstyle</artifactId>
                    <version>${checkstyle.version}</version>
                </dependency>
                <dependency>
                    <groupId>com.github.sevntu.checkstyle</groupId>
                    <artifactId>sevntu-checkstyle-maven-plugin</artifactId>
                    <version>${sevntu-checkstyle-maven-plugin.version}</version>
                </dependency>
                <dependency>
                    <groupId>net.kemitix</groupId>
                    <artifactId>kemitix-checkstyle-ruleset</artifactId>
                    <version>${kemitix-checkstyle-ruleset.version}</version>
                </dependency>
                <configuration>
                    <configLocation>net/kemitix/checkstyle.xml</configLocation>
                </configuration>
            </dependencies>
        </plugin><!-- maven-checkstyle-plugin -->
    </plugins>
</pluginManagement>
<plugins>
    <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-checkstyle-plugin</artifactId>
        <executions>
            <execution>
                <id>validate</id>
                <phase>validate</phase>
                <goals>
                    <goal>check</goal>
                    <goal>checkstyle</goal>
                </goals>
            </execution>
        </executions>
    </plugin><!-- maven-checkstyle-plugin -->
</plugins>

All Checks

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 {}

AbstractClassName

The name of an abstract class must start with Abstract. Classes that start with Abstract must be abstract.

Valid:

abstract class AbstractCardHand implements CardHand {}

Invalid:

abstract class BaseCardHand implements CardHand {}

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 ...
 */

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())
{
    // ...
}

AvoidStarImport

Prevents the use of the star import.

Invalid:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;

AvoidStaticImport

Prevents importing static members, unless they are one of the following:

  • org.assertj.core.api.Assertions.assertThat
  • org.mockito.BDDMockito.given
  • org.mockito.Mockito.*
  • org.mockito.Matchers.*
  • org.mockito.Mockito.*

Valid:

import static org.assertj.core.api.Assertions.assertThat;
import static org.mockito.BDDMockito.given;

Invalid:

import static java.nio.charset.StandardCharsets.UTF_8;

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() ; ) {}

EmptyLineSeparator

Checks that there are blank lines between header, package, import blocks, field, constructors, methods, nested classes, static initialisers and instance initialisers.

Valid:

/**
 * Licence header.
 */

package net.kemitix.foo;

import ...;
import ...;

class Foo {

    private int a;

    private int b;

    Foo() {}

    Foo(int a, int b) {}

    int getA() {}

    int getB() {}

    class Bar {
    }
}

Invalid:

/**
 * Licence header.
 */
package net.kemitix.foo;
import ...;
import ...;
class Foo {
    private int a;
    private int b;
    Foo() {}
    Foo(int a, int b) {}
    int getA() {}
    int getB() {}
    class Bar {
    }
}

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

Valid:

class Valid {

    private int foo;

    private Object bar;
}

Invalid:

class Invalid {

    private int 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() {}
}

FinalLocalVariable

Checks that local variables are final if they are never modified after declaration.

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);

Header

Checks that all *.java source files begin with the contents of the LICENSE.txt file.

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 {}

JavadocMethod

Checks that all public, protected and package methods have a Javadoc block, that all @throws tags are used. Basic setters and getters do not require javadoc.

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. The @author tag must have a name and, in brackets, an email address.

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.

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.

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 --;

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.

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

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 );

RedundantModifier

Checks for redundant modifiers. Checks for:

  • Interface and annotation definitions.
  • Final modifier on methods of final and anonymous classes.
  • Inner interface declarations that are declared as static.
  • Class constructors.
  • Nested enum definitions that are declared as static.

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:

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)) {}

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

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) {}

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();
}

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())) {}

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.

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.

EnumValueName

Forces Enum values to be all upper-case when the enum has no methods or fields, otherwise the values must must be either all upper-case or must match the class naming format.

Valid:

enum ValidConstants {

    ALPHA, BETA;
}

enum ValidClassLike {

    Alpha("a"),
    Beta("b");

    private String name;

    ValidClassLike(String name) {
        this.name = name;
    }
}

Invalid:

enum InvalidConstants {

    alpha, Beta;
}

enum InvalidClassLike {

    alpha("a"),
    beta("b");

    private String name;

    InvalidClassLike(String name) {
        this.name = name;
    }
}

ForbidCCommentsInMethods

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

Valid:

void doSomething() {
    // a comment
}

Invalid:

void doSomething() {
    /* invalid */
}

ForbidReturnInFinallyBlock

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

Invalid:

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

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.

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;
}

ReturnBooleanFromTernary

Ternary statements shouldn't have Boolean values as results.

Valid:

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

Invalid:

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

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

Checks that setters and getters follow the normal setField(), getField() and isField() pattern, where 'Field' is the name of the field being accessed.

SingleBreakOrContinue

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

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 al exceptions and then just rethrow them.

Invalid:

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

UselessSuperCtorCall

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

Invalid:

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

Disabled Checks

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

Checkstyle

ArrayTrailingComma

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

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.

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.

Checks for redundant imports. Checks for duplicates, imports from the java.lang package or from the current package.

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.

RegexpSingleline

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.

TODO: disable

AvoidDefaultSerializableInInnerClasses

TODO: enable

AvoidModifiersForTypes

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

CauseParameterInException

Should already be covered by AvoidHidingCauseException.

ChildBlockLength

Appears to be broken as of 1.21.0.

CustomDeclarationOrder

The DeclarationOrder check already imposes an order for class elements.

EmptyPublicCtorInClass

TODO: enable

FinalizeImplementation

TODO: enable

ForbidAnnotation

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

ForbidCertainImports

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

ForbidInstantiation

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

ForbidThrowAnonymousExceptions

IllegalThrows performs a similar check.

HideUtilityClassConstructor

See HideUtilityClassConstructor.

IllegalCatchExtended

See IllegalCatch.

InnerClass

See InnerTypeLast.

InterfaceTypeParameterName

See InterfaceTypeParameterName.

LineLengthExtended

See LineLength

MultipleStringLiteralsExtended

See MultipleStringLiteralsExtended.

MultipleVariableDeclarationsExtended

See MultipleVariableDeclarations.

RequiredParameterForAnnotation

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

ReturnCountExtended

See ReturnCount.

StaticMethodCandidate

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

UnnecessaryParenthesesExtended

See UnnecessaryParentheses.

WhitespaceBeforeArrayInitializer

TODO: enable