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:
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hide.utility.class
- Since:
- 3.1
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Nested Class Summary
Nested ClassesModifier and TypeClassDescriptionprivate static class
Details of class that are required for validation.Nested classes/interfaces inherited from class com.puppycrawl.tools.checkstyle.api.AutomaticBean
AutomaticBean.OutputStreamOptions
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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.private static boolean
isAbstract
(DetailAST ast) Returns true if given class is abstract or false.private static boolean
Returns true if given class is static or false.void
visitToken
(DetailAST ast) Called to process a token.Methods inherited from class com.puppycrawl.tools.checkstyle.api.AbstractCheck
beginTree, clearViolations, destroy, finishTree, getFileContents, getLine, getLineCodePoints, getLines, getTabWidth, getTokenNames, getViolations, 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
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Field Details
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MSG_KEY
A key is pointing to the warning message text in "messages.properties" file.- See Also:
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Constructor Details
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HideUtilityClassConstructorCheck
public HideUtilityClassConstructorCheck()
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Method Details
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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:
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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:
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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:
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visitToken
Description copied from class:AbstractCheck
Called to process a token.- Overrides:
visitToken
in classAbstractCheck
- Parameters:
ast
- the token to process
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isAbstract
Returns true if given class is abstract or false.- Parameters:
ast
- class definition for check.- Returns:
- true if a given class declared as abstract.
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isStatic
Returns true if given class is static or false.- Parameters:
ast
- class definition for check.- Returns:
- true if a given class declared as static.
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