Class ThrowsCountCheck

  • All Implemented Interfaces:
    Configurable, Contextualizable

    public final class ThrowsCountCheck
    extends AbstractCheck

    Restricts throws statements to a specified count. Methods with "Override" or "java.lang.Override" annotation are skipped from validation as current class cannot change signature of these methods.

    Rationale: Exceptions form part of a method's interface. Declaring a method to throw too many differently rooted exceptions makes exception handling onerous and leads to poor programming practices such as writing code like catch(Exception ex). 4 is the empirical value which is based on reports that we had for the ThrowsCountCheck over big projects such as OpenJDK. This check also forces developers to put exceptions into a hierarchy such that in the simplest case, only one type of exception need be checked for by a caller but any subclasses can be caught specifically if necessary. For more information on rules for the exceptions and their issues, see Effective Java: Programming Language Guide Second Edition by Joshua Bloch pages 264-273.

    ignorePrivateMethods - allows to skip private methods as they do not cause problems for other classes.

    • Property max - Specify maximum allowed number of throws statements. Type is int. Default value is 4.
    • Property ignorePrivateMethods - Allow private methods to be ignored. Type is boolean. Default value is true.

    To configure check:

     <module name="ThrowsCount"/>
     

    Example:

     class Test {
         public void myFunction() throws CloneNotSupportedException,
                                 ArrayIndexOutOfBoundsException,
                                 StringIndexOutOfBoundsException,
                                 IllegalStateException,
                                 NullPointerException { // violation, max allowed is 4
             // body
         }
    
         public void myFunc() throws ArithmeticException,
                 NumberFormatException { // ok
             // body
         }
    
         private void privateFunc() throws CloneNotSupportedException,
                                 ClassNotFoundException,
                                 IllegalAccessException,
                                 ArithmeticException,
                                 ClassCastException { // ok, private methods are ignored
             // body
         }
    
     }
     

    To configure the check so that it doesn't allow more than two throws per method:

     <module name="ThrowsCount">
       <property name="max" value="2"/>
     </module>
     

    Example:

     class Test {
         public void myFunction() throws IllegalStateException,
                                     ArrayIndexOutOfBoundsException,
                                     NullPointerException { // violation, max allowed is 2
             // body
         }
    
         public void myFunc() throws ArithmeticException,
                                     NumberFormatException { // ok
             // body
         }
    
         private void privateFunc() throws CloneNotSupportedException,
                                     ClassNotFoundException,
                                     IllegalAccessException,
                                     ArithmeticException,
                                     ClassCastException { // ok, private methods are ignored
             // body
         }
    
     }
     

    To configure the check so that it doesn't skip private methods:

     <module name="ThrowsCount">
       <property name="ignorePrivateMethods" value="false"/>
     </module>
     

    Example:

     class Test {
         public void myFunction() throws CloneNotSupportedException,
                                     ArrayIndexOutOfBoundsException,
                                     StringIndexOutOfBoundsException,
                                     IllegalStateException,
                                     NullPointerException { // violation, max allowed is 4
             // body
         }
    
         public void myFunc() throws ArithmeticException,
                                     NumberFormatException { // ok
             // body
         }
    
         private void privateFunc() throws CloneNotSupportedException,
                                     ClassNotFoundException,
                                     IllegalAccessException,
                                     ArithmeticException,
                                     ClassCastException { // violation, max allowed is 4
             // body
         }
    
         private void func() throws IllegalStateException,
                                     NullPointerException { // ok
             // body
         }
    
     }
     

    Parent is com.puppycrawl.tools.checkstyle.TreeWalker

    Violation Message Keys:

    • throws.count
    Since:
    3.2
    • Constructor Detail

      • ThrowsCountCheck

        public ThrowsCountCheck()
        Creates new instance of the check.
    • Method Detail

      • 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
      • setIgnorePrivateMethods

        public void setIgnorePrivateMethods​(boolean ignorePrivateMethods)
        Setter to allow private methods to be ignored.
        Parameters:
        ignorePrivateMethods - whether private methods must be ignored.
      • setMax

        public void setMax​(int max)
        Setter to specify maximum allowed number of throws statements.
        Parameters:
        max - maximum allowed throws statements.
      • visitLiteralThrows

        private void visitLiteralThrows​(DetailAST ast)
        Checks number of throws statements.
        Parameters:
        ast - throws for check.
      • isOverriding

        private static boolean isOverriding​(DetailAST ast)
        Check if a method has annotation @Override.
        Parameters:
        ast - throws, which is being checked.
        Returns:
        true, if a method has annotation @Override.
      • getAnnotationName

        private static String getAnnotationName​(DetailAST annotation)
        Gets name of an annotation.
        Parameters:
        annotation - to get name of.
        Returns:
        name of an annotation.
      • isInPrivateMethod

        private static boolean isInPrivateMethod​(DetailAST ast)
        Checks if method, which throws an exception is private.
        Parameters:
        ast - throws, which is being checked.
        Returns:
        true, if method, which throws an exception is private.