Package com.puppycrawl.tools.checkstyle.checks.design

Class HideUtilityClassConstructorCheck

java.lang.Object
com.puppycrawl.tools.checkstyle.AbstractAutomaticBean
com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter
com.puppycrawl.tools.checkstyle.api.AbstractCheck
com.puppycrawl.tools.checkstyle.checks.design.HideUtilityClassConstructorCheck
All Implemented Interfaces:
Configurable, Contextualizable
public class HideUtilityClassConstructorCheck extends AbstractCheck
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) {
     // ...
   }
 }
  • Property ignoreAnnotatedBy - Ignore classes annotated with the specified annotation(s). Annotation names provided in this property must exactly match the annotation names on the classes. If the target class has annotations specified with their fully qualified names (including package), the annotations in this property should also be specified with their fully qualified names. Similarly, if the target class has annotations specified with their simple names, this property should contain the annotations with the same simple names. Type is java.lang.String[]. Default value is "".

Parent is com.puppycrawl.tools.checkstyle.TreeWalker

Violation Message Keys:

  • hide.utility.class
Since:
3.1

  • Field Details

    • MSG_KEY

      public static final String MSG_KEY
      A key is pointing to the warning message text in "messages.properties" file.
      See Also:

    • ignoreAnnotatedBy

      private Set<String> ignoreAnnotatedBy
      Ignore classes annotated with the specified annotation(s). Annotation names provided in this property must exactly match the annotation names on the classes. If the target class has annotations specified with their fully qualified names (including package), the annotations in this property should also be specified with their fully qualified names. Similarly, if the target class has annotations specified with their simple names, this property should contain the annotations with the same simple names.

  • Constructor Details

  • Method Details

    • setIgnoreAnnotatedBy

      public void setIgnoreAnnotatedBy(String... annotationNames)
      Setter to ignore classes annotated with the specified annotation(s). Annotation names provided in this property must exactly match the annotation names on the classes. If the target class has annotations specified with their fully qualified names (including package), the annotations in this property should also be specified with their fully qualified names. Similarly, if the target class has annotations specified with their simple names, this property should contain the annotations with the same simple names.
      Parameters:
      annotationNames - specified annotation(s)
      Since:
      10.20.0

    • 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 class AbstractCheck
      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 class AbstractCheck
      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 class AbstractCheck
      Returns:
      the token set this must be registered for.
      See Also:

    • visitToken

      public void visitToken(DetailAST ast)
      Description copied from class: AbstractCheck
      Called to process a token.
      Overrides:
      visitToken in class AbstractCheck
      Parameters:
      ast - the token to process

    • isAbstract

      private static boolean isAbstract(DetailAST ast)
      Returns true if given class is abstract or false.
      Parameters:
      ast - class definition for check.
      Returns:
      true if a given class declared as abstract.

    • isStatic

      private static boolean isStatic(DetailAST ast)
      Returns true if given class is static or false.
      Parameters:
      ast - class definition for check.
      Returns:
      true if a given class declared as static.

    • shouldIgnoreClass

      private boolean shouldIgnoreClass(DetailAST ast)
      Checks if class is annotated by specific annotation(s) to skip.
      Parameters:
      ast - class to check
      Returns:
      true if annotated by ignored annotations