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

Class RedundantModifierCheck

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.modifier.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.
  7. strictfp modifier when using JDK 17 or later. See reason at JEP 306
  8. final modifier on unnamed variables when using JDK 22 or later.

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();
 }

Parent is com.puppycrawl.tools.checkstyle.TreeWalker

Violation Message Keys:

  • redundantModifier
Since:
3.0

  • 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:

    • TOKENS_FOR_INTERFACE_MODIFIERS

      private static final int[] TOKENS_FOR_INTERFACE_MODIFIERS
      An array of tokens for interface modifiers.

    • JDK_22

      private static final int JDK_22
      Constant for jdk 22 version number.
      See Also:

    • JDK_17

      private static final int JDK_17
      Constant for jdk 17 version number.
      See Also:

    • jdkVersion

      private int jdkVersion
      Set the JDK version that you are using. Old JDK version numbering is supported (e.g. 1.8 for Java 8) as well as just the major JDK version alone (e.g. 8) is supported. This property only considers features from officially released Java versions as supported. Features introduced in preview releases are not considered supported until they are included in a non-preview release.

  • Constructor Details

  • Method Details

    • setJdkVersion

      public void setJdkVersion(String jdkVersion)
      Setter to set the JDK version that you are using. Old JDK version numbering is supported (e.g. 1.8 for Java 8) as well as just the major JDK version alone (e.g. 8) is supported. This property only considers features from officially released Java versions as supported. Features introduced in preview releases are not considered supported until they are included in a non-preview release.
      Parameters:
      jdkVersion - the Java version
      Since:
      10.18.0

    • 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:

    • 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:

    • 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:

    • 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

    • processLambdaParameters

      private void processLambdaParameters(DetailAST lambdaAst)
      Process lambda parameters.
      Parameters:
      lambdaAst - node of type TokenTypes.LAMBDA

    • checkUnnamedVariables

      private void checkUnnamedVariables(DetailAST ast)
      Check if the variable is unnamed and has redundant final modifier.
      Parameters:
      ast - node of type TokenTypes.VARIABLE_DEF or TokenTypes.PATTERN_VARIABLE_DEF or TokenTypes.PARAMETER_DEF

    • isUnnamedVariable

      private static boolean isUnnamedVariable(DetailAST ast)
      Check if the variable is unnamed.
      Parameters:
      ast - node of type TokenTypes.VARIABLE_DEF or TokenTypes.PATTERN_VARIABLE_DEF or TokenTypes.PARAMETER_DEF
      Returns:
      true if the variable is unnamed

    • checkConstructorModifiers

      private void checkConstructorModifiers(DetailAST ctorDefAst)
      Check modifiers of constructor.
      Parameters:
      ctorDefAst - ast node of type TokenTypes.CTOR_DEF

    • checkInterfaceModifiers

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

    • checkEnumConstructorModifiers

      private void checkEnumConstructorModifiers(DetailAST ast)
      Check if enum constructor has proper modifiers.
      Parameters:
      ast - constructor of enum

    • processInterfaceOrAnnotation

      private void processInterfaceOrAnnotation(DetailAST ast)
      Do validation of interface of annotation.
      Parameters:
      ast - token AST

    • processMethods

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

    • processAbstractMethodParameters

      private void processAbstractMethodParameters(DetailAST ast)
      Process validation of parameters for Methods with no definition.
      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<DetailAST> getMethodAnnotationsList(DetailAST methodDef)
      Gets the list of annotations on method definition.
      Parameters:
      methodDef - method definition node
      Returns:
      List of annotations