Package com.puppycrawl.tools.checkstyle.checks.modifier

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. Inner interface declarations that are declared as static.
    4. Class constructors.
    5. Nested enum definitions that are declared as static.

    Interfaces by definition are abstract so the abstract modifier on the interface is redundant.

    Classes inside of interfaces by definition are public and static, so the public and static modifiers on the inner classes 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.

    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

    • Field Detail

      • MSG_KEY

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

    • Constructor Detail

      • RedundantModifierCheck

        public RedundantModifierCheck()

    • Method Detail

      • 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:
        TokenTypes

      • 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:
        TokenTypes

      • 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