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 Details

  • Constructor Details

    • BooleanExpressionComplexityCheck

      public BooleanExpressionComplexityCheck()
      Creates new instance of the check.
  • Method Details

    • 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:
    • 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.
    • 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
    • isPassedInParameter

      private static boolean isPassedInParameter(DetailAST logicalOperator)
      Checks if logical operator is part of constructor or method call.
      Parameters:
      logicalOperator - logical operator
      Returns:
      true if logical operator is part of constructor or method call
    • isPipeOperator

      private static boolean isPipeOperator(DetailAST binaryOr)
      Checks if binary OR is applied to exceptions in multi-catch (pipe-syntax).
      Parameters:
      binaryOr - binary or
      Returns:
      true if binary or is applied to exceptions in multi-catch.
    • 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
    • visitMethodDef

      private void visitMethodDef(DetailAST ast)
      Creates new context for a given method.
      Parameters:
      ast - a method we start to check.
    • leaveMethodDef

      private void leaveMethodDef()
      Removes old context.
    • visitExpr

      private void visitExpr()
      Creates and pushes new context.
    • leaveExpr

      private void leaveExpr(DetailAST ast)
      Restores previous context.
      Parameters:
      ast - expression we leave.