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

Class InterfaceIsTypeCheck

  • All Implemented Interfaces:
    Configurable, Contextualizable
    public final class InterfaceIsTypeCheck
extends AbstractCheck

    Implements Joshua Bloch, Effective Java, Item 17 - Use Interfaces only to define types.

    According to Bloch, an interface should describe a type. It is therefore inappropriate to define an interface that does not contain any methods but only constants. The Standard interface javax.swing.SwingConstants is an example of an interface that would be flagged by this check.

    The check can be configured to also disallow marker interfaces like java.io.Serializable, that do not contain methods or constants at all.

    • Property allowMarkerInterfaces - Control whether marker interfaces like Serializable are allowed. Type is boolean. Default value is true.

    To configure the check: 

     <module name="InterfaceIsType"/>

    Example:

     public interface Test1 { // violation
     int a = 3;

 }

 public interface Test2 { // OK

 }

 public interface Test3 { // OK
     int a = 3;
     void test();
 }

    To configure the check to report violation so that it doesn't allow Marker Interfaces: 

     <module name="InterfaceIsType">
   <property name="allowMarkerInterfaces" value="false"/>
 </module>

    Example:

     public interface Test1 { // violation
     int a = 3;
 }

 public interface Test2 { // violation

 }

    Parent is com.puppycrawl.tools.checkstyle.TreeWalker

    Violation Message Keys:

    • interface.type
    Since:
    3.1

    • 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

      • InterfaceIsTypeCheck

        public InterfaceIsTypeCheck()

    • 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

      • setAllowMarkerInterfaces

        public void setAllowMarkerInterfaces​(boolean flag)
        Setter to control whether marker interfaces like Serializable are allowed.
        Parameters:
        flag - whether to allow marker interfaces or not