Class MutableExceptionCheck

  • All Implemented Interfaces:
    Configurable, Contextualizable

    public final class MutableExceptionCheck
    extends AbstractCheck

    Ensures that exception classes (classes with names conforming to some pattern and explicitly extending classes with names conforming to other pattern) are immutable, that is, that they have only final fields.

    The current algorithm is very simple: it checks that all members of exception are final. The user can still mutate an exception's instance (e.g. Throwable has a method called setStackTrace which changes the exception's stack trace). But, at least, all information provided by this exception type is unchangeable.

    Rationale: Exception instances should represent an error condition. Having non-final fields not only allows the state to be modified by accident and therefore mask the original condition but also allows developers to accidentally forget to set the initial state. In both cases, code catching the exception could draw incorrect conclusions based on the state.

    • Property format - Specify pattern for exception class names. Type is java.util.regex.Pattern. Default value is "^.*Exception$|^.*Error$|^.*Throwable$".
    • Property extendedClassNameFormat - Specify pattern for extended class names. Type is java.util.regex.Pattern. Default value is "^.*Exception$|^.*Error$|^.*Throwable$".

    To configure the check:

     <module name="MutableException"/>
     

    Parent is com.puppycrawl.tools.checkstyle.TreeWalker

    Violation Message Keys:

    • mutable.exception
    Since:
    3.2
    • Method Detail

      • setExtendedClassNameFormat

        public void setExtendedClassNameFormat​(Pattern extendedClassNameFormat)
        Setter to specify pattern for extended class names.
        Parameters:
        extendedClassNameFormat - a String value
      • setFormat

        public void setFormat​(Pattern pattern)
        Setter to specify pattern for exception class names.
        Parameters:
        pattern - the new pattern
      • 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
      • visitClassDef

        private void visitClassDef​(DetailAST ast)
        Called when we start processing class definition.
        Parameters:
        ast - class definition node
      • leaveClassDef

        private void leaveClassDef()
        Called when we leave class definition.
      • visitVariableDef

        private void visitVariableDef​(DetailAST ast)
        Checks variable definition.
        Parameters:
        ast - variable def node for check
      • isNamedAsException

        private boolean isNamedAsException​(DetailAST ast)
        Checks that a class name conforms to specified format.
        Parameters:
        ast - class definition node
        Returns:
        true if a class name conforms to specified format
      • isExtendedClassNamedAsException

        private boolean isExtendedClassNamedAsException​(DetailAST ast)
        Checks that if extended class name conforms to specified format.
        Parameters:
        ast - class definition node
        Returns:
        true if extended class name conforms to specified format