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

Class 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 Detail

      • 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.

    • Method Detail

      • 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

      • 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:
        TokenTypes

      • 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