Miscellaneous Checkstyle Development Team

Checks whether files end with a line separator.

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

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"
fileExtensions file type extension of the files to check. String Set all files

To configure the check:

<module name="NewlineAtEndOfFile"/>

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

<module name="NewlineAtEndOfFile"> <property name="lineSeparator" value="lf"/> </module>

To configure the check to work only on Java, XML and Python files:

<module name="NewlineAtEndOfFile"> <property name="fileExtensions" value="java, xml, py"/> </module>

com.puppycrawl.tools.checkstyle.checks

Checker

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 the format property.

name description type default value
format Pattern to match comments against regular expression TODO:

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.

To configure the check:

<module name="TodoComment"/>

To configure the check for comments that contain WARNING:

<module name="TodoComment"> <property name="format" value="WARNING"/> </module>

com.puppycrawl.tools.checkstyle.checks

TreeWalker

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:

#messages.properties hello=Hello cancel=Cancel #messages_de.properties hell=Hallo ok=OK

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:

messages_de.properties: Key 'hello' missing. messages_de.properties: Key 'cancel' missing. messages.properties: Key 'hell' missing. messages.properties: Key 'ok' missing.
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
basenameSeparator Allows setting file names separator String _

To configure the check for files with '_' name separator:

<module name="Translation"/>

To configure the check for files with user-set name separator:

<module name="Translation"> <property name="basenameSeparator" value="STRING_LITERAL"/> </module>

com.puppycrawl.tools.checkstyle.checks

Checker

Checks for uncommented main() methods.

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

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

To configure the check:

<module name="UncommentedMain"/>

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

<module name="UncommentedMain"> <property name="excludedClasses" value="\.Main$"/> </module>

com.puppycrawl.tools.checkstyle.checks

TreeWalker

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

The capital L looks a lot like 1.

To configure the check:

<module name="UpperEll"/>

com.puppycrawl.tools.checkstyle.checks

TreeWalker

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[])

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

To configure the check to enforce Java style:

<module name="ArrayTypeStyle"/>

To configure the check to enforce C style:

<module name="ArrayTypeStyle"> <property name="javaStyle" value="false"/> </module>

com.puppycrawl.tools.checkstyle.checks

TreeWalker

Check that parameters for methods, constructors, and catch blocks 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.

name description type default value
tokens blocks to check subset of tokens METHOD_DEF, CTOR_DEF, LITERAL_CATCH METHOD_DEF, CTOR_DEF
ignorePrimitiveTypes ignore primitive types as parameters Boolean false

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

<module name="FinalParameters"/>

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

<module name="FinalParameters"> <property name="tokens" value="CTOR_DEF"/> </module>

To configure the check to allow ignoring primitive datatypes as parameters:

<module name="FinalParameters"> <property name="ignorePrimitiveTypes" value="true"/> </module>

com.puppycrawl.tools.checkstyle.checks

TreeWalker

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 recommend using other checks when they provide the desired functionality. Essentially, this check just works on the level of an abstract syntax tree and knows nothing about language structures.

name description type default value
tokens token types to check subset of tokens declared in TokenTypes empty set
limitedTokens set of tokens with limited occurrences as descendants subset of tokens declared in TokenTypes empty set
minimumDepth the minimum 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 the minimum count is not reached String "descendant.token.min"
maximumMessage error message when the maximum count is exceeded String "descendant.token.max"

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

<module name="DescendantToken"> <property name="tokens" value="EQUAL,NOT_EQUAL"/> <property name="limitedTokens" value="LITERAL_THIS,LITERAL_NULL"/> <property name="maximumNumber" value="1"/> <property name="maximumDepth" value="1"/> <property name="sumTokenCounts" value="true"/> </module>

String literal equality check:

<module name="DescendantToken"> <property name="tokens" value="EQUAL,NOT_EQUAL"/> <property name="limitedTokens" value="STRING_LITERAL"/> <property name="maximumNumber" value="0"/> <property name="maximumDepth" value="1"/> </module>

Switch with no default:

<module name="DescendantToken"> <property name="tokens" value="LITERAL_SWITCH"/> <property name="maximumDepth" value="2"/> <property name="limitedTokens" value="LITERAL_DEFAULT"/> <property name="minimumNumber" value="1"/> </module>

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

<module name="DescendantToken"> <property name="tokens" value="LITERAL_ASSERT"/> <property name="limitedTokens" value="ASSIGN,DEC,INC,POST_DEC, POST_INC,PLUS_ASSIGN,MINUS_ASSIGN,STAR_ASSIGN,DIV_ASSIGN,MOD_ASSIGN, BSR_ASSIGN,SR_ASSIGN,SL_ASSIGN,BAND_ASSIGN,BXOR_ASSIGN,BOR_ASSIGN, METHOD_CALL"/> <property name="maximumNumber" value="0"/> </module>

The initialiser in for performs no setup (where a while statement could be used instead):

<module name="DescendantToken"> <property name="tokens" value="FOR_INIT"/> <property name="limitedTokens" value="EXPR"/> <property name="minimumNumber" value="1"/> </module>

The condition in for performs no check:

<module name="DescendantToken"> <property name="tokens" value="FOR_CONDITION"/> <property name="limitedTokens" value="EXPR"/> <property name="minimumNumber" value="1"/> </module>

A switch within a switch:

<module name="DescendantToken"> <property name="tokens" value="LITERAL_SWITCH"/> <property name="limitedTokens" value="LITERAL_SWITCH"/> <property name="maximumNumber" value="0"/> <property name="minimumDepth" value="1"/> </module>

A return statement from within a catch or finally block:

<module name="DescendantToken"> <property name="tokens" value="LITERAL_FINALLY,LITERAL_CATCH"/> <property name="limitedTokens" value="LITERAL_RETURN"/> <property name="maximumNumber" value="0"/> </module>

A try statement within a catch or finally block:

<module name="DescendantToken"> <property name="tokens" value="LITERAL_CATCH,LITERAL_FINALLY"/> <property name="limitedTokens" value="LITERAL_TRY"/> <property name="maximumNumber" value="0"/> </module>

Too many cases within a switch:

<module name="DescendantToken"> <property name="tokens" value="LITERAL_SWITCH"/> <property name="limitedTokens" value="LITERAL_CASE"/> <property name="maximumDepth" value="2"/> <property name="maximumNumber" value="10"/> </module>

Too many local variables within a method:

<module name="DescendantToken"> <property name="tokens" value="METHOD_DEF"/> <property name="limitedTokens" value="VARIABLE_DEF"/> <property name="maximumDepth" value="2"/> <property name="maximumNumber" value="10"/> </module>

Too many returns from within a method:

<module name="DescendantToken"> <property name="tokens" value="METHOD_DEF"/> <property name="limitedTokens" value="LITERAL_RETURN"/> <property name="maximumNumber" value="3"/> </module>

Too many fields within an interface:

<module name="DescendantToken"> <property name="tokens" value="INTERFACE_DEF"/> <property name="limitedTokens" value="VARIABLE_DEF"/> <property name="maximumDepth" value="2"/> <property name="maximumNumber" value="0"/> </module>

Limits the number of exceptions a method can throw:

<module name="DescendantToken"> <property name="tokens" value="LITERAL_THROWS"/> <property name="limitedTokens" value="IDENT"/> <property name="maximumNumber" value="1"/> </module>

Limits the number of expressions in a method:

<module name="DescendantToken"> <property name="tokens" value="METHOD_DEF"/> <property name="limitedTokens" value="EXPR"/> <property name="maximumNumber" value="200"/> </module>

Disallows empty statements:

<module name="DescendantToken"> <property name="tokens" value="EMPTY_STAT"/> <property name="limitedTokens" value="EMPTY_STAT"/> <property name="maximumNumber" value="0"/> <property name="maximumDepth" value="0"/> <property name="maximumMessage" value="Empty statement is not allowed."/> </module>

Too many fields within a class:

<module name="DescendantToken"> <property name="tokens" value="CLASS_DEF"/> <property name="limitedTokens" value="VARIABLE_DEF"/> <property name="maximumDepth" value="2"/> <property name="maximumNumber" value="10"/> </module>

com.puppycrawl.tools.checkstyle.checks

TreeWalker

Checks correct indentation of Java code.

The idea behind this is that while pretty printers are sometimes convenient 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 is followed.

name description type default value
basicOffset how many spaces to use for new indentation level Integer 4
braceAdjustment how far braces should be indented when on the next line Integer 0
caseIndent how much to indent a case label Integer 4
throwsIndent how far a throws clause should be indented when on next line Integer 4
arrayInitIndent how much to indent an array initialisation when on next line Integer 4
lineWrappingIndentation how far continuation line should be indented when line-wrapping is present Integer 4
forceStrictCondition force strict condition in line wrapping case. If value is true, line wrap indent have to be same as lineWrappingIndentation parameter Boolean false

To configure the check:

<module name="Indentation"/>

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

<module name="Indentation"> <property name="caseIndent" value="0"/> </module>

To configure the Check to enforce strict condition in line-wrapping validation.

<module name="Indentation"> <property name="forceStrictCondition" value="true"/> </module>

Such config doesn't allow next cases:

void foo(String aFooString, int aFooInt) {} // indent:8 ; expected: 4; warn, because 8 != 4

But if forceStrictCondition = false, this code is valid:

void foo(String aFooString, int aFooInt) {} // indent:8 ; expected: > 4; ok, because 8 > 4

com.puppycrawl.tools.checkstyle.checks.indentation

TreeWalker

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 a line; for example, it accepts 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:

a = b + c; // Some insightful comment d = e / f; // Another comment for this line

Quoting Code Complete for the justification:

  • "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."

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

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

To configure the check:

<module name="TrailingComment"/>

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

<module name="TrailingComment"> <property name="format" value="^\\s*$"/> </module>

com.puppycrawl.tools.checkstyle.checks.indentation

TreeWalker

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 except supplying the regular expression from a file.

It differs from them in that it works in multiline mode. Its 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 the beginning of a line, as opposed to beginning of the input.
  • For beginning of the input use \A.
  • $ means the end of a line, as opposed to the end of the input.
  • For end of input use \Z.
  • Each line in the file is terminated with a line feed character.

Note: Not all regular expression 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 achieve 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.

name description type default value
format pattern regular expression $^ (empty)
message message which is used to notify about violations, if empty then the 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

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

To use like Required Regexp check:

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

The statement.

// This code is copyrighted

The check.

<module name="Regexp"> <property name="format" value="// This code is copyrighted"/> </module>

Your statement may be multiline.

// This code is copyrighted // (c) MyCompany

Then the check would be.

<module name="Regexp"> <property name="format" value="// This code is copyrighted\n// \(c\) MyCompany"/> </module>

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:

<module name="Regexp"> <property name="format" value="// This code is copyrighted\n// \(c\) MyCompany"/> <property name="duplicateLimit" value="0"/> </module>

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

<module name="Regexp"> <property name="format" value="// This code is copyrighted\n// \(c\) MyCompany"/> <property name="message" value="Copyright"/> </module>

To use like illegal regexp check:

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

<module name="Regexp"> <!-- . matches any character, so we need to escape it and use \. to match dots. --> <property name="format" value="System\.out\.println"/> <property name="illegalPattern" value="true"/> </module>

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

<module name="Regexp"> <property name="format" value="System\.out\.println"/> <property name="illegalPattern" value="true"/> <property name="ignoreComments" value="true"/> </module>

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

<module name="Regexp"> <property name="format" value="[ \t]+$"/> <property name="illegalPattern" value="true"/> <property name="message" value="Trailing whitespace"/> </module>

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

<module name="Regexp"> <property name="format" value="(?i)debug"/> <property name="illegalPattern" value="true"/> </module>

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.

<module name="Regexp"> <property name="format" value="(?i)debug"/> <property name="illegalPattern" value="true"/> <property name="errorLimit" value="1000"/> </module>

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.
// Copyright (C) 2004 MyCompany // All rights reserved <module name="Regexp"> <property name="format" value="\A// Copyright \(C\) \d\d\d\d MyCompany\n// All rights reserved"/> </module>

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

/////////////////////////////////////////////////////////////////////// // checkstyle: // Checks Java source code for adherence to a set of rules. // Copyright (C) 2004 Oliver Burn // Last modification by $Author A.N.Other$ /////////////////////////////////////////////////////////////////////// package com.puppycrawl.checkstyle; import java.util.thing1; import java.util.thing2; import java.util.thing3; /** * javadoc line 1 * javadoc line 2 * javadoc line 3 */ <module name="Regexp"> <property name="format" value="\A/{71}\n// checkstyle:\n// Checks Java source code for adherence to a set of rules\.\n// Copyright \(C\) \d\d\d\d Oliver Burn\n // Last modification by \$Author.*\$\n/{71}\n\npackage [\w\.]*;\n\n (import [\w\.]*;\n)*\n/\*\*\n( \*[^/]*\n)* \*/"/> </module>

More examples:

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

/* * PID.java * * Copyright (c) 2001 ACME * 123 Some St. * Somewhere. * * This software is the confidential and proprietary information of ACME. * ("Confidential Information"). You shall not disclose such * Confidential Information and shall use it only in accordance with * the terms of the license agreement you entered into with ACME. * * $Log: config_misc.xml,v $ * Revision 1.7 2007/01/16 12:16:35 oburn * Removing all reference to mailing lists * * Revision 1.6 2005/12/25 16:13:10 o_sukhodolsky * Fix for rfe 1248106 (TYPECAST is now accepted by NoWhitespaceAfter) * * Fix for rfe 953266 (thanks to Paul Guyot (pguyot) for submitting patch) * IllegalType can be configured to accept some abstract classes which * matches to regexp of illegal type names (property legalAbstractClassNames) * * TrailingComment now can be configured to accept some trailing comments * (such as NOI18N) (property legalComment, rfe 1385344). * * Revision 1.5 2005/11/06 11:54:12 oburn * Incorporate excellent patch [ 1344344 ] Consolidation of regexp checks. * * Revision 1.3.8.1 2005/10/11 14:26:32 someone * Fix for bug 251. The broken bit is fixed */ package com.acme.tools; import com.acme.thing1; import com.acme.thing2; import com.acme.thing3; /** * * <P> * <I>This software is the confidential and proprietary information of * ACME (<B>"Confidential Information"</B>). You shall not * disclose such Confidential Information and shall use it only in * accordance with the terms of the license agreement you entered into * with ACME.</I> * </P> * * &#169; copyright 2002 ACME * * @author Some Body */ public class PID extends StateMachine implements WebObject.Constants { /** javadoc. */ public static final int A_SETPOINT = 1; . . . } // class PID

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.
<module name="Regexp"> <property name="format" value="\A/\*\n \* (\w*)\.java\n \*\n \* Copyright \(c\) \d\d\d\d ACME\n \* 123 Some St\.\n \* Somewhere\.\n \*\n \* This software is the confidential and proprietary information of ACME\.\n \* \("Confidential Information"\)\. You shall not disclose such\n \* Confidential Information and shall use it only in accordance with\n \* the terms of the license agreement you entered into with ACME\.\n \*\n \* \$Log: config_misc.xml,v $ \* \Revision 1.7 2007/01/16 12:16:35 oburn \* \Removing all reference to mailing lists \* \ \* \Revision 1.6 2005/12/25 16:13:10 o_sukhodolsky \* \Fix for rfe 1248106 (TYPECAST is now accepted by NoWhitespaceAfter) \* \ \* \Fix for rfe 953266 (thanks to Paul Guyot (pguyot) for submitting patch) \* \IllegalType can be configured to accept some abstract classes which \* \matches to regexp of illegal type names (property legalAbstractClassNames) \* \ \* \TrailingComment now can be configured to accept some trailing comments \* \(such as NOI18N) (property legalComment, rfe 1385344). \* \ \* \Revision 1.5 2005/11/06 11:54:12 oburn \* \Incorporate excellent patch [ 1344344 ] Consolidation of regexp checks. \* \\n(.*\n)*([\w|\s]*( class | interface )\1)"/> <property name="message" value="Correct header not found"/> </module>

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

<module name="Regexp"> <property name="format" value="(/\*\*\n)( \*.*\n)*( \* &lt;P&gt;\n \* &lt;I&gt; This software is the confidential and proprietary information of\n \* ACME \(&lt;B&gt;&quot;Confidential Information&quot;&lt;/B&gt; \)\. You shall not\n \* disclose such Confidential Information and shall use it only in\n \* accordance with the terms of the license agreement you entered into\n \* with ACME\.&lt;/I&gt;\n \* &lt;/P&gt;\n \*\n \* &#169; copyright \d\d\d\d ACME\n \*\n \* @author .*)(\n\s\*.*)*/\n[\w|\s]*( class | interface )"/> <property name="message" value="Copyright in class/interface Javadoc"/> <property name="duplicateLimit" value="0"/> </module>

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.

com.puppycrawl.tools.checkstyle.checks

TreeWalker

Checks that the outer type name and the file name match. For example, the class Foo must be in a file named Foo.java.

None.

To configure the check:

<module name="OuterTypeFilename"/>

com.puppycrawl.tools.checkstyle.checks

TreeWalker

Checks properties files for duplicated properties.

Rationale: Multiple property keys usually appear after merge or rebase of several branches. While there are no errors in runtime, there can be a confusion due to having different values for the duplicated properties.

name description type default value
fileExtensions file type extension of the files to check. String Set properties

To configure the check:

<module name="UniqueProperties"> <property name="fileExtensions" value="properties" /> </module>

com.puppycrawl.tools.checkstyle.checks

Checker

Restrict using Unicode escapes (e.g. \u221e). It is possible to allow using escapes for non-printable(control) characters. Also, this check can be configured to allow using escapes if trail comment is present. By the option it is possible to allow using escapes if literal contains only them.

name description type default value
allowEscapesForControlCharacters Allow use escapes for non-printable(control) characters. Boolean false
allowByTailComment Allow use escapes if trail comment is present. Boolean false
allowIfAllCharactersEscaped Allow if all characters in literal are escaped. Boolean false
allowNonPrintableEscapes Allow non-printable escapes. Boolean false

Examples of using Unicode:

String unitAbbrev = "μs"; //Best: perfectly clear even without a comment. String unitAbbrev = "\u03bcs"; //Poor: the reader has no idea what this is.

An example of how to configure the check is:

<module name="AvoidEscapedUnicodeCharacters"/>

An example of non-printable(control) characters.

return '\ufeff' + content; // byte order mark

An example of how to configure the check to allow using escapes for non-printable(control) characters:

<module name="AvoidEscapedUnicodeCharacters"> <property name="allowEscapesForControlCharacters" value="true"/> </module>

Example of using escapes with trail comment:

String unitAbbrev = "\u03bcs"; // Greek letter mu, "s"

An example of how to configure the check to allow using escapes if trail comment is present:

<module name="AvoidEscapedUnicodeCharacters"> <property name="allowByTailComment" value="true"/> </module>

Example of using escapes if literal contains only them:

String unitAbbrev = "\u03bc\u03bc\u03bc";

An example of how to configure the check to allow escapes if literal contains only them:

<module name="AvoidEscapedUnicodeCharacters"> <property name="allowIfAllCharactersEscaped" value="true"/> </module>

An example of how to configure the check to allow non-printable escapes:

<module name="AvoidEscapedUnicodeCharacters"> <property name="allowNonPrintableEscapes" value="true"/> </module>

com.puppycrawl.tools.checkstyle.checks

TreeWalker

Checks properties file for a duplicated properties.

Rationale: Multiple property keys usually appears after merge or rebase of several branches. While there is no errors in runtime, there can be a confusion on having different values for the duplicated properties.

name description type default value
fileExtensions file type extension of the files to check. String Set properties

To configure the check:

<module name="UniqueProperties"> <property name="fileExtensions" value="properties" /> </module>

com.puppycrawl.tools.checkstyle.checks

Checker