Class HideUtilityClassConstructorCheck
java.lang.Object
com.puppycrawl.tools.checkstyle.api.AutomaticBean
com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter
com.puppycrawl.tools.checkstyle.api.AbstractCheck
com.puppycrawl.tools.checkstyle.checks.design.HideUtilityClassConstructorCheck
- All Implemented Interfaces:
Configurable
,Contextualizable
Makes sure that utility classes (classes that contain only static methods or fields in their API) do not have a public constructor.
Rationale: Instantiating utility classes does not make sense. Hence the constructors should either be private or (if you want to allow subclassing) protected. A common mistake is forgetting to hide the default constructor.
If you make the constructor protected you may want to consider the following constructor implementation technique to disallow instantiating subclasses:
public class StringUtils // not final to allow subclassing { protected StringUtils() { // prevents calls from subclass throw new UnsupportedOperationException(); } public static int count(char c, String s) { // ... } }
To configure the check:
<module name="HideUtilityClassConstructor"/>
Example:
class Test { // violation, class only has a static method and a constructor public Test() { } public static void fun() { } } class Foo { // OK private Foo() { } static int n; } class Bar { // OK protected Bar() { // prevents calls from subclass throw new UnsupportedOperationException(); } } class UtilityClass { // violation, class only has a static field static float f; }
Parent is com.puppycrawl.tools.checkstyle.TreeWalker
Violation Message Keys:
-
hide.utility.class
- Since:
- 3.1
-
Nested Class Summary
Nested classes/interfaces inherited from class com.puppycrawl.tools.checkstyle.api.AutomaticBean
AutomaticBean.OutputStreamOptions
-
Field Summary
Fields -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionint[]
The configurable token set.int[]
Returns the default token a check is interested in.int[]
The tokens that this check must be registered for.void
visitToken
(DetailAST ast) Called to process a token.Methods inherited from class com.puppycrawl.tools.checkstyle.api.AbstractCheck
beginTree, clearMessages, destroy, finishTree, getFileContents, getLine, getLines, getMessages, getTabWidth, getTokenNames, init, isCommentNodesRequired, leaveToken, log, log, log, setFileContents, setTabWidth, setTokens
Methods inherited from class com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter
finishLocalSetup, getCustomMessages, getId, getMessageBundle, getSeverity, getSeverityLevel, setId, setSeverity
Methods inherited from class com.puppycrawl.tools.checkstyle.api.AutomaticBean
configure, contextualize, getConfiguration, setupChild
-
Field Details
-
MSG_KEY
A key is pointing to the warning message text in "messages.properties" file.- See Also:
-
-
Constructor Details
-
HideUtilityClassConstructorCheck
public HideUtilityClassConstructorCheck()
-
-
Method Details
-
getDefaultTokens
public int[] getDefaultTokens()Description copied from class:AbstractCheck
Returns the default token a check is interested in. Only used if the configuration for a check does not define the tokens.- Specified by:
getDefaultTokens
in classAbstractCheck
- Returns:
- the default tokens
- See Also:
-
getAcceptableTokens
public int[] getAcceptableTokens()Description copied from class:AbstractCheck
The configurable token set. Used to protect Checks against malicious users who specify an unacceptable token set in the configuration file. The default implementation returns the check's default tokens.- Specified by:
getAcceptableTokens
in classAbstractCheck
- Returns:
- the token set this check is designed for.
- See Also:
-
getRequiredTokens
public int[] getRequiredTokens()Description copied from class:AbstractCheck
The tokens that this check must be registered for.- Specified by:
getRequiredTokens
in classAbstractCheck
- Returns:
- the token set this must be registered for.
- See Also:
-
visitToken
Description copied from class:AbstractCheck
Called to process a token.- Overrides:
visitToken
in classAbstractCheck
- Parameters:
ast
- the token to process
-