Miscellaneous

NewlineAtEndOfFile

Description

Checks whether files end with a new line.

Rationale: Any source files and text files in general should end with a newline character, especially when using SCM systems such as CVS. CVS will even print a warning when it encounters a file that doesn't end with a newline.

Properties

name	description	type	default value
lineSeparator	type of line separator	One of "system" (system default), "crlf" (Windows-style), "cr" (Mac-style) and "lf" (Unix-style)	system default
fileExtensions	file type extension of the files to check.	String Set	all files

Examples

To configure the check:

To configure the check to always use Unix-style line separators:

To configure the check to work only on java, xml and python files:

Package

com.puppycrawl.tools.checkstyle.checks

Parent Module

Checker

TodoComment

Description

A check for TODO: comments. Actually it is a generic regular expression matcher on Java comments. To check for other patterns in Java comments, set property format.

Properties

name	description	type	default value
format	pattern to check	regular expression	TODO:

Notes

Using TODO: comments is a great way to keep track of tasks that need to be done. Having them reported by Checkstyle makes it very hard to forget about them.

Examples

To configure the check:

To configure the check for comments that contain WARNING:

Package

com.puppycrawl.tools.checkstyle.checks

Parent Module

TreeWalker

Translation

Description

A FileSetCheck that ensures the correct translation of code by checking property files for consistency regarding their keys. Two property files describing one and the same context are consistent if they contain the same keys.

Consider the following properties file in the same directory:

The Translation check will find the typo in the german hello key, the missing ok key in the default resource file and the missing cancel key in the german resource file:

Properties

name	description	type	default value
fileExtensions	file type extension to identify translation files. Setting this property is typically only required if your translation files are preprocessed and the original files do not have the extension .properties	String Set	properties

Example

To configure the check:

Package

com.puppycrawl.tools.checkstyle.checks

Parent Module

Checker

UncommentedMain

Description

Checks for uncommented main() methods (debugging leftovers).

Rationale: A main() method is often used for debug puposes. When debugging is finished, developers often forget to remove the method, which changes the API and increases the size of the resulting class/jar file. With the exception of the real program entry points, all main() methods should be removed/commented out of the sources.

Properties

name	description	type	default value
excludedClasses	pattern for qualified names of classes which are allowed to have a main method.	regular expression	^$

Examples

To configure the check:

To configure the check to allow main method for all classes with "Main" name:

Package

com.puppycrawl.tools.checkstyle.checks

Parent Module

TreeWalker

UpperEll

Description

Checks that long constants are defined with an upper ell. That is ' L' and not 'l'. This is in accordance to the Java Language Specification, Section 3.10.1.

looks a lot like 1.

Examples

To configure the check:

Package

com.puppycrawl.tools.checkstyle.checks

Parent Module

TreeWalker

ArrayTypeStyle

Description

Checks the style of array type definitions. Some like Java-style: public static void main(String[] args) and some like C-style: public static void main(String args[])

Properties

name	description	type	default value
javaStyle	Controls whether to enforce Java style (true) or C style (false).	Boolean	true

Examples

To configure the check to enforce Java style:

To configure the check to enforce C style:

Package

com.puppycrawl.tools.checkstyle.checks

Parent Module

TreeWalker

FinalParameters

Description

Check that method/constructor/catch block parameters are final. Interface and abstract methods are not checked - the final keyword does not make sense for interface and abstract method parameters as there is no code that could modify the parameter.

Rationale: Changing the value of parameters during the execution of the method's algorithm can be confusing and should be avoided. A great way to let the Java compiler prevent this coding style is to declare parameters final.

Properties

name	description	type	default value
tokens	blocks to check	subset of tokens METHOD_DEF, CTOR_DEF, LITERAL_CATCH	METHOD_DEF, CTOR_DEF

Examples

To configure the check to enforce final parameters for methods and constructors:

To configure the check to enforce final parameters only for constructors:

Package

com.puppycrawl.tools.checkstyle.checks

Parent Module

TreeWalker

DescendantToken

Description

Checks for restricted tokens beneath other tokens.

WARNING: This is a very powerful and flexible check, but, at the same time, it is low level and very implementation dependent because its results depend on the grammar we use to build abstract syntax trees. Thus we recomend using other checks when they provide the desired funcionality. All in all, this check just works on the level of an abstract tree and knows nothing about language structures.

Properties

name	description	type	default value
tokens	token types to check	subset of tokens declared in TokenTypes	empty set
limitedTokens	set of tokens with limited occurances as descendants	subset of tokens declared in TokenTypes	empty set
minimumDepth	the mimimum depth for descendant counts	Integer	0
maximumDepth	the maximum depth for descendant counts	Integer	java.lang.Integer.MAX_VALUE
minimumNumber	a minimum count for descendants	Integer	0
maximumNumber	a maximum count for descendants	Integer	java.lang.Integer.MAX_VALUE
sumTokenCounts	whether the number of tokens found should be calculated from the sum of the individual token counts	Boolean	false
minimumMessage	error message when minimum count not reached	String	"descendant.token.min"
maximumMessage	error message when maximum count exceeded	String	"descendant.token.max"

Examples

Comparing this with null (i.e. this == null and this != null):

String literal equality check:

Switch with no default:

Assert statement may have side effects (formatted for browser display):

Initialiser in for performs no setup (use while instead?):

Condition in for performs no check:

Switch within switch:

Return from within a catch or finally block:

Try within catch or finally block:

Too many cases within a switch:

Too many local variables within a method:

Too many returns from within a method:

Too many fields within an interface:

Limit the number of exceptions a method can throw:

Limit the number of expressions in a method:

Disallow empty statements:

Too many fields within a class:

Package

com.puppycrawl.tools.checkstyle.checks

Parent Module

TreeWalker

Indentation

Description

Checks correct indentation of Java Code.

The basic idea behind this is that while pretty printers are sometimes convienent for bulk reformats of legacy code, they often either aren't configurable enough or just can't anticipate how format should be done. Sometimes this is personal preference, other times it is practical experience. In any case, this check should just ensure that a minimal set of indentation rules are followed.

Properties

name	description	type	default value
basicOffset	how many spaces to use for new indentation level	Integer	4
braceAdjustment	how far brace should be indented when on next line	Integer	0
caseIndent	how much to indent a case label	Integer	4

Examples

To configure the check:

To configure the check to enforce indentation style recommended by Sun:

Package

com.puppycrawl.tools.checkstyle.checks.indentation

Parent Module

TreeWalker

TrailingComment

Description

The check to ensure that requires that comments be the only thing on a line. For the case of // comments that means that the only thing that should precede it is whitespace. It doesn't check comments if they do not end line, i.e. it accept the following: Thread.sleep( 10 <some comment here> ); Format property is intended to deal with the "} // while" example.

Rationale: Steve McConnel in "Code Complete" suggests that endline comments are a bad practice. An end line comment would be one that is on the same line as actual code. For example:

Quoting "Code Complete" for the justfication:

• "The comments have to be aligned so that they do not interfere with the visual structure of the code. If you don't align them neatly, they'll make your listing look like it's been through a washing machine."
• "Endline comments tend to be hard to format...It takes time to align them. Such time is not spent learning more about the code; it's dedicated solely to the tedious task of pressing the spacebar or tab key."
• "Endline comments are also hard to maintain. If the code on any line containing an endline comment grows, it bumps the comment farther out, and all the other endline comments will have to bumped out to match. Styles that are hard to maintain aren't maintained...."
• "Endline comments also tend to be cryptic. The right side of the line doesn't offer much room and the desire to keep the comment on one line means the comment must be short. Work then goes into making the line as short as possible instead of as clear as possible. The comment usually ends up as cryptic as possible...."
• "A systemic problem with endline comments is that it's hard to write a meaningful comment for one line of code. Most endline comments just repeat the line of code, which hurts more than it helps."

His comments on being hard to maintain when the size of the line changes are even more important in the age of automated refactorings.

Properties

name	description	type	default value
format	pattern for string allowed before comment.	regular expression	^[\\s\\}\\);]*$
legalComment	pattern for text of trailing comment which is allowed. (this patter will not be applied to multiline comments and text of comment will be trimmed before matching)	regular expression	(not set)

Examples

To configure the check:

To configure the check so it enforces only comment on a line:

Package

com.puppycrawl.tools.checkstyle.checks.indentation

Parent Module

TreeWalker

Regexp

Description

A check that makes sure that a specified pattern exists, exists less than a set number of times, or does not exist in the file.

This check combines all the functionality provided by RegexpHeader, GenericIllegalRegexp and RequiredRegexp, except supplying the regular expression from a file.

It differs from them in that it works in multiline mode. It's regular expression can span multiple lines and it checks this against the whole file at once. The others work in singleline mode. Their single or multiple regular expressions can only span one line. They check each of these against each line in the file in turn.

Note: Because of the different mode of operation there may be some changes in the regular expressions used to achieve a particular end.

In multiline mode...

• ^ means beginning of a line, as oposed to beginning of input.
• For beginning of input use \A.
• $ means end of a line, as oposed to end of input.
• For end of input use \Z.
• Each line in the file is terminated with a newline character.

Note: Not all regexp engines are created equal. Some provide extra functions that others do not and some elements of the syntax may vary. This check makes use of the java.util.regex package, please check its documentation for details of how to construct a regular expression to achive a particular goal.

Note: When entering a regular expression as a parameter in the xml config file you must also take into account the xml rules. e.g. if you want to match a < symbol you need to enter &lt;. The regular expression should be entered on one line.

Properties

name	description	type	default value
format	pattern	regular expression	$^ (empty)
message	message which is used to notify about violations, if empty then default(hard-coded) message is used.	String	""(empty)
illegalPattern	Controls whether the pattern is required or illegal.	Boolean	false
duplicateLimit	Controls whether to check for duplicates of a required pattern, any negative value means no checking for duplicates, any positive value is used as the maximum number of allowed duplicates, if the limit is exceeded errors will be logged.	Integer	-1
errorLimit	Controls the maximum number of errors before the check will abort.	Integer	100
ignoreComments	Controls whether to ignore matches found within comments.	Boolean	false

Examples

The following examples are mainly copied from the other 3 checks mentioned above, to show how the same results can be acheived using this check in place of them.

To use like RequiredRegexp :

An example of how to configure the check to make sure a copyright statement is included in the file:

The statement.

The check.

Your statement may be multiline.

Then the check would be.

Note: To search for parentheses () in a regular expression you must escape them like \(\). This is required by the regexp engine, otherwise it will think they are special instruction characters.

And to make sure it appears only once:

It can also be useful to attach a meaningful message to the check:

To use like GenericIllegalRegexp :

An example of how to configure the check to make sure there are no calls to System.out.println:

You may want to make the above check ignore comments, like this:

An example of how to configure the check to find trailing whitespace at the end of a line:

Note: The difference between this and the example given for GenericIllegalRegexp is necessary because \s and $ both match the newline character ("\n").

An example of how to configure the check to find case-insensitive occurrences of "debug":

Note: The (?i) at the beginning of the regular expression tells the regexp engine to ignore the case.

There is also a feature to limit the number of errors reported. When the limit is reached the check aborts with a message reporting that the limit has been reached. The default limit setting is 100, but this can be change as shown in the following example.

To use like RegexpHeader :

To configure the check to verify that each file starts with the following multiline header.

Note the following:

• \A means the start of the file.
• The date can be any 4 digit number.

A more complex example. Note how the import and javadoc multilines are handled, there can be any number of them.

More examples:

The next 2 examples deal with the following example java source file:

This checks for the presence of the header, the first 16 lines.

Note the following:

• Line 2 and 13 contain the file name. These are checked to make sure they are the same, and that they match the class name.
• The date can be any 4 digit number.

This checks for the presence of a copyright notice within the class javadoc, lines 24 to 37.

Note: To search for things that mean something in xml, like < you need to escape them like &lt;. This is required so the xml parser does not act on them, but instead passes the correct character to the regexp engine.

Package

com.puppycrawl.tools.checkstyle.checks

Parent Module

TreeWalker