Package com.puppycrawl.tools.checkstyle.checks.metrics

Class CyclomaticComplexityCheck

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

    Checks cyclomatic complexity against a specified limit. It is a measure of the minimum number of possible paths through the source and therefore the number of required tests, it is not a about quality of code! It is only applied to methods, c-tors, static initializers and instance initializers.

    The complexity is equal to the number of decision points + 1. Decision points: if, while, do, for, ?:, catch, switch, case statements and operators && and || in the body of target.

    By pure theory level 1-4 is considered easy to test, 5-7 OK, 8-10 consider re-factoring to ease testing, and 11+ re-factor now as testing will be painful.

    When it comes to code quality measurement by this metric level 10 is very good level as a ultimate target (that is hard to archive). Do not be ashamed to have complexity level 15 or even higher, but keep it below 20 to catch really bad designed code automatically.

    Please use Suppression to avoid violations on cases that could not be split in few methods without damaging readability of code or encapsulation.

    To configure the check: 

     <module name="CyclomaticComplexity"/>

    Example: 

     class CyclomaticComplexity {
   // Cyclomatic Complexity = 11
   int a, b, c, d, n;
   public void foo() { // 1, function declaration
     if (a == 1) { // 2, if
       fun1();
     } else if (a == b // 3, if
       && a == c) { // 4, && operator
       if (c == 2) { // 5, if
         fun2();
       }
     } else if (a == d) { // 6, if
       try {
         fun4();
       } catch (Exception e) { // 7, catch
       }
     } else {
       switch(n) {
         case 1: // 8, case
           fun1();
           break;
         case 2: // 9, case
           fun2();
           break;
         case 3: // 10, case
           fun3();
           break;
         default:
           break;
       }
     }
     d = a < 0 ? -1 : 1; // 11, ternary operator
   }
 }

    To configure the check with a threshold of 4 and check only for while and do-while loops: 

     <module name="CyclomaticComplexity">
   <property name="max" value="4"/>
   <property name="tokens" value="LITERAL_WHILE, LITERAL_DO"/>
 </module>

    Example: 

     class CyclomaticComplexity {
   // Cyclomatic Complexity = 5
   int a, b, c, d;
   public void foo() { // 1, function declaration
     while (a < b // 2, while
       && a > c) {
       fun();
     }
     if (a == b) {
       do { // 3, do
         fun();
       } while (d);
     } else if (c == d) {
       while (c > 0) { // 4, while
         fun();
       }
       do { // 5, do-while
         fun();
       } while (a);
     }
   }
 }

    To configure the check to consider switch-case block as one decision point. 

     <module name="CyclomaticComplexity">
   <property name="switchBlockAsSingleDecisionPoint" value="true"/>
 </module>

    Example: 

     class CyclomaticComplexity {
   // Cyclomatic Complexity = 11
   int a, b, c, d, e, n;
   public void foo() { // 1, function declaration
     if (a == b) { // 2, if
       fun1();
     } else if (a == 0 // 3, if
       && b == c) { // 4, && operator
       if (c == -1) { // 5, if
         fun2();
       }
     } else if (a == c // 6, if
       || a == d) { // 7, || operator
       fun3();
     } else if (d == e) { // 8, if
       try {
         fun4();
       } catch (Exception e) { // 9, catch
       }
     } else {
       switch(n) { // 10, switch
         case 1:
           fun1();
           break;
         case 2:
           fun2();
           break;
         default:
           break;
       }
     }
     a = a > 0 ? b : c; // 11, ternary operator
   }
 }

    Parent is com.puppycrawl.tools.checkstyle.TreeWalker

    Violation Message Keys:

    • cyclomaticComplexity
    Since:
    3.2

    • 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

      • CyclomaticComplexityCheck

        public CyclomaticComplexityCheck()

    • Method Detail

      • setSwitchBlockAsSingleDecisionPoint

        public void setSwitchBlockAsSingleDecisionPoint​(boolean switchBlockAsSingleDecisionPoint)
        Setter to control whether to treat the whole switch block as a single decision point.
        Parameters:
        switchBlockAsSingleDecisionPoint - whether to treat the whole switch block as a single decision point.

      • setMax

        public final void setMax​(int max)
        Setter to specify the maximum threshold allowed.
        Parameters:
        max - the maximum threshold

      • 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

      • 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

      • getRequiredTokens

        public final 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

      • 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