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

Class MutableExceptionCheck

java.lang.Object
com.puppycrawl.tools.checkstyle.api.AutomaticBean
com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter
com.puppycrawl.tools.checkstyle.api.AbstractCheck
com.puppycrawl.tools.checkstyle.checks.design.MutableExceptionCheck
All Implemented Interfaces:
Configurable, Contextualizable
public final class MutableExceptionCheck extends AbstractCheck

Ensures that exception classes (classes with names conforming to some regular expression and explicitly extending classes with names conforming to other regular expression) 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

  • 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:

  • Constructor Details

    • MutableExceptionCheck

      public MutableExceptionCheck()

  • Method Details

    • 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

    • 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

    • leaveToken

      public void leaveToken(DetailAST ast)
      Description copied from class: AbstractCheck
      Called after all the child nodes have been process.
      Overrides:
      leaveToken in class AbstractCheck
      Parameters:
      ast - the token leaving