Class RedundantModifierCheck

  • All Implemented Interfaces:
    Configurable, Contextualizable

    public class RedundantModifierCheck
    extends AbstractCheck

    Checks for redundant modifiers.

    Rationale: The Java Language Specification strongly discourages the usage of public and abstract for method declarations in interface definitions as a matter of style.

    The check validates:

    1. Interface and annotation definitions.
    2. Final modifier on methods of final and anonymous classes.
    3. Type declarations nested under interfaces that are declared as public or static.
    4. Class constructors.
    5. Nested enum definitions that are declared as static.
    6. record definitions that are declared as final and nested record definitions that are declared as static.

    interfaces by definition are abstract so the abstract modifier is redundant on them.

    Type declarations nested under interfaces by definition are public and static, so the public and static modifiers on nested type declarations are redundant. On the other hand, classes inside of interfaces can be abstract or non abstract. So, abstract modifier is allowed.

    Fields in interfaces and annotations are automatically public, static and final, so these modifiers are redundant as well.

    As annotations are a form of interface, their fields are also automatically public, static and final just as their annotation fields are automatically public and abstract.

    A record class is implicitly final and cannot be abstract, these restrictions emphasize that the API of a record class is defined solely by its state description, and cannot be enhanced later by another class. Nested records are implicitly static. This avoids an immediately enclosing instance which would silently add state to the record class. See JEP 395 for more info.

    Enums by definition are static implicit subclasses of java.lang.Enum<E>. So, the static modifier on the enums is redundant. In addition, if enum is inside of interface, public modifier is also redundant.

    Enums can also contain abstract methods and methods which can be overridden by the declared enumeration fields. See the following example:

     public enum EnumClass {
       FIELD_1,
       FIELD_2 {
         @Override
         public final void method1() {} // violation expected
       };
    
       public void method1() {}
       public final void method2() {} // no violation expected
     }
     

    Since these methods can be overridden in these situations, the final methods are not marked as redundant even though they can't be extended by other classes/enums.

    Nested enum types are always static by default.

    Final classes by definition cannot be extended so the final modifier on the method of a final class is redundant.

    Public modifier for constructors in non-public non-protected classes is always obsolete:

     public class PublicClass {
       public PublicClass() {} // OK
     }
    
     class PackagePrivateClass {
       public PackagePrivateClass() {} // violation expected
     }
     

    There is no violation in the following example, because removing public modifier from ProtectedInnerClass constructor will make this code not compiling:

     package a;
     public class ClassExample {
       protected class ProtectedInnerClass {
         public ProtectedInnerClass () {}
       }
     }
    
     package b;
     import a.ClassExample;
     public class ClassExtending extends ClassExample {
       ProtectedInnerClass pc = new ProtectedInnerClass();
     }
     

    To configure the check:

     <module name="RedundantModifier"/>
     

    To configure the check to check only methods and not variables:

     <module name="RedundantModifier">
       <property name="tokens" value="METHOD_DEF"/>
     </module>
     

    Parent is com.puppycrawl.tools.checkstyle.TreeWalker

    Violation Message Keys:

    • redundantModifier
    Since:
    3.0
    • Method Detail

      • 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
      • checkInterfaceModifiers

        private void checkInterfaceModifiers​(DetailAST ast)
        Checks if interface has proper modifiers.
        Parameters:
        ast - interface to check
      • processMethods

        private void processMethods​(DetailAST ast)
        Process validation of Methods.
        Parameters:
        ast - method AST
      • checkClassConstructorModifiers

        private void checkClassConstructorModifiers​(DetailAST classCtorAst)
        Check if class constructor has proper modifiers.
        Parameters:
        classCtorAst - class constructor ast
      • processResources

        private void processResources​(DetailAST ast)
        Checks if given resource has redundant modifiers.
        Parameters:
        ast - ast
      • checkForRedundantModifier

        private void checkForRedundantModifier​(DetailAST ast,
                                               int... modifierTypes)
        Checks if given ast has a redundant modifier.
        Parameters:
        ast - ast
        modifierTypes - The modifiers to check for.
      • isClassProtected

        private static boolean isClassProtected​(DetailAST classDef)
        Checks if given class ast has protected modifier.
        Parameters:
        classDef - class ast
        Returns:
        true if class is protected, false otherwise
      • isClassPublic

        private static boolean isClassPublic​(DetailAST ast)
        Checks if given class is accessible from "public" scope.
        Parameters:
        ast - class def to check
        Returns:
        true if class is accessible from public scope,false otherwise
      • isEnumMember

        private static boolean isEnumMember​(DetailAST ast)
        Checks if current AST node is member of Enum.
        Parameters:
        ast - AST node
        Returns:
        true if it is an enum member
      • isInterfaceOrAnnotationMember

        private static boolean isInterfaceOrAnnotationMember​(DetailAST ast)
        Checks if current AST node is member of Interface or Annotation, not of their subnodes.
        Parameters:
        ast - AST node
        Returns:
        true or false
      • isAnnotatedWithSafeVarargs

        private static boolean isAnnotatedWithSafeVarargs​(DetailAST methodDef)
        Checks if method definition is annotated with. SafeVarargs annotation
        Parameters:
        methodDef - method definition node
        Returns:
        true or false
      • getMethodAnnotationsList

        private static List<DetailASTgetMethodAnnotationsList​(DetailAST methodDef)
        Gets the list of annotations on method definition.
        Parameters:
        methodDef - method definition node
        Returns:
        List of annotations