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

Class BooleanExpressionComplexityCheck

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

    Restricts the number of boolean operators (&&, ||, &, | and ^) in an expression.

    Rationale: Too many conditions leads to code that is difficult to read and hence debug and maintain.

    Note that the operators & and | are not only integer bitwise operators, they are also the non-shortcut versions of the boolean operators && and ||.

    Note that &, | and ^ are not checked if they are part of constructor or method call because they can be applied to non boolean variables and Checkstyle does not know types of methods from different classes.

    • Property max - Specify the maximum number of boolean operations allowed in one expression. Type is int. Default value is 3.
    • Property tokens - tokens to check Type is java.lang.String[]. Validation type is tokenSet. Default value is: LAND, BAND, LOR, BOR, BXOR.

    To configure the check: 

     <module name="BooleanExpressionComplexity"/>

    Code Example:

     public class Test
 {
 public static void main(String ... args)
 {
 boolean a = true;
 boolean b = false;

 boolean c = (a & b) | (b ^ a);       // OK, 1(&) + 1(|) + 1(^) = 3 (max allowed 3)

 boolean d = (a & b) ^ (a || b) | a;  // violation, 1(&) + 1(^) + 1(||) + 1(|) = 4
 }
 }

    To configure the check with 5 allowed operation in boolean expression: 

     <module name="BooleanExpressionComplexity">
   <property name="max" value="5"/>
 </module>

    Code Example:

     public class Test
 {
  public static void main(String ... args)
  {
   boolean a = true;
   boolean b = false;

   boolean c = (a & b) | (b ^ a) | (a ^ b);   // OK, 1(&) + 1(|) + 1(^) + 1(|) + 1(^) = 5

   boolean d = (a | b) ^ (a | b) ^ (a || b) & b; // violation,
                                               // 1(|) + 1(^) + 1(|) + 1(^) + 1(||) + 1(&) = 6
  }
 }

    To configure the check to ignore &amp; and |: 

     <module name="BooleanExpressionComplexity">
   <property name="tokens" value="BXOR,LAND,LOR"/>
 </module>

    Code Example:

     public class Test
 {
  public static void main(String ... args)
   {
     boolean a = true;
     boolean b = false;

     boolean c = (!a && b) | (a || !b) ^ a;    // OK, 1(&&) + 1(||) + 1(^) = 3
                                                // | is ignored here

     boolean d = a ^ (a || b) ^ (b || a) & a; // violation, 1(^) + 1(||) + 1(^) + 1(||) = 4
                                               // & is ignored here
    }
  }

    Parent is com.puppycrawl.tools.checkstyle.TreeWalker

    Violation Message Keys:

    • booleanExpressionComplexity
    Since:
    3.4

    • 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

      • BooleanExpressionComplexityCheck

        public BooleanExpressionComplexityCheck()
        Creates new instance of the check.

    • 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

      • setMax

        public void setMax​(int max)
        Setter to specify the maximum number of boolean operations allowed in one expression.
        Parameters:
        max - new maximum allowed complexity.

      • 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