Class VariableDeclarationUsageDistanceCheck

  • All Implemented Interfaces:
    Configurable, Contextualizable

    public class VariableDeclarationUsageDistanceCheck
    extends AbstractCheck

    Checks the distance between declaration of variable and its first usage. Note : Variable declaration/initialization statements are not counted while calculating length.

    • Property allowedDistance - Specify distance between declaration of variable and its first usage. Values should be greater than 0. Type is int. Default value is 3.
    • Property ignoreVariablePattern - Define RegExp to ignore distance calculation for variables listed in this pattern. Type is java.util.regex.Pattern. Default value is "".
    • Property validateBetweenScopes - Allow to calculate the distance between declaration of variable and its first usage in the different scopes. Type is boolean. Default value is false.
    • Property ignoreFinal - Allow to ignore variables with a 'final' modifier. Type is boolean. Default value is true.

    To configure the check with default config:

     <module name="VariableDeclarationUsageDistance"/>
     

    Example:

     public class Test {
    
       public void foo1() {
         int num;        // violation, distance = 4
         final int PI;   // OK, final variables not checked
         System.out.println("Statement 1");
         System.out.println("Statement 2");
         System.out.println("Statement 3");
         num = 1;
         PI = 3.14;
       }
    
       public void foo2() {
         int a;          // OK, used in different scope
         int b;          // OK, used in different scope
         int count = 0;  // OK, used in different scope
    
         {
           System.out.println("Inside inner scope");
           a = 1;
           b = 2;
           count++;
         }
       }
     }
     

    Check can detect a block of initialization methods. If a variable is used in such a block and there are no other statements after variable declaration, then distance = 1.

    Case #1:

     int minutes = 5;
     Calendar cal = Calendar.getInstance();
     cal.setTimeInMillis(timeNow);
     cal.set(Calendar.SECOND, 0);
     cal.set(Calendar.MILLISECOND, 0);
     cal.set(Calendar.HOUR_OF_DAY, hh);
     cal.set(Calendar.MINUTE, minutes);
     

    The distance for the variable "minutes" is 1 even though this variable is used in the fifth method's call.

    Case #2:

     int minutes = 5;
     Calendar cal = Calendar.getInstance();
     cal.setTimeInMillis(timeNow);
     cal.set(Calendar.SECOND, 0);
     cal.set(Calendar.MILLISECOND, 0);
     System.out.println(cal);
     cal.set(Calendar.HOUR_OF_DAY, hh);
     cal.set(Calendar.MINUTE, minutes);
     

    The distance for the variable "minutes" is 6 because there is one more expression (except the initialization block) between the declaration of this variable and its usage.

    To configure the check to set allowed distance:

     <module name="VariableDeclarationUsageDistance">
       <property name="allowedDistance" value="4"/>
     </module>
     

    Example:

     public class Test {
    
       public void foo1() {
         int num;        // OK, distance = 4
         final int PI;   // OK, final variables not checked
         System.out.println("Statement 1");
         System.out.println("Statement 2");
         System.out.println("Statement 3");
         num = 1;
         PI = 3.14;
       }
    
       public void foo2() {
         int a;          // OK, used in different scope
         int b;          // OK, used in different scope
         int count = 0;  // OK, used in different scope
    
         {
           System.out.println("Inside inner scope");
           a = 1;
           b = 2;
           count++;
         }
       }
     }
     

    To configure the check to ignore certain variables:

     <module name="VariableDeclarationUsageDistance">
       <property name="ignoreVariablePattern" value="^num$"/>
     </module>
     

    This configuration ignores variables named "num".

    Example:

     public class Test {
    
       public void foo1() {
         int num;        // OK, variable ignored
         final int PI;   // OK, final variables not checked
         System.out.println("Statement 1");
         System.out.println("Statement 2");
         System.out.println("Statement 3");
         num = 1;
         PI = 3.14;
       }
    
       public void foo2() {
         int a;          // OK, used in different scope
         int b;          // OK, used in different scope
         int count = 0;  // OK, used in different scope
    
         {
           System.out.println("Inside inner scope");
           a = 1;
           b = 2;
           count++;
         }
       }
     }
     

    To configure the check to force validation between scopes:

     <module name="VariableDeclarationUsageDistance">
       <property name="validateBetweenScopes" value="true"/>
     </module>
     

    Example:

     public class Test {
    
       public void foo1() {
         int num;        // violation, distance = 4
         final int PI;   // OK, final variables not checked
         System.out.println("Statement 1");
         System.out.println("Statement 2");
         System.out.println("Statement 3");
         num = 1;
         PI = 3.14;
       }
    
       public void foo2() {
         int a;          // OK, distance = 2
         int b;          // OK, distance = 3
         int count = 0;  // violation, distance = 4
    
         {
           System.out.println("Inside inner scope");
           a = 1;
           b = 2;
           count++;
         }
       }
     }
     

    To configure the check to check final variables:

     <module name="VariableDeclarationUsageDistance">
       <property name="ignoreFinal" value="false"/>
     </module>
     

    Example:

     public class Test {
    
       public void foo1() {
         int num;        // violation, distance = 4
         final int PI;   // violation, distance = 5
         System.out.println("Statement 1");
         System.out.println("Statement 2");
         System.out.println("Statement 3");
         num = 1;
         PI = 3.14;
       }
    
       public void foo2() {
         int a;          // OK, used in different scope
         int b;          // OK, used in different scope
         int count = 0;  // OK, used in different scope
    
         {
           System.out.println("Inside inner scope");
           a = 1;
           b = 2;
           count++;
         }
       }
     }
     

    Parent is com.puppycrawl.tools.checkstyle.TreeWalker

    Violation Message Keys:

    • variable.declaration.usage.distance
    • variable.declaration.usage.distance.extend
    Since:
    5.8
    • Method Detail

      • setAllowedDistance

        public void setAllowedDistance​(int allowedDistance)
        Setter to specify distance between declaration of variable and its first usage. Values should be greater than 0.
        Parameters:
        allowedDistance - Allowed distance between declaration of variable and its first usage.
      • setIgnoreVariablePattern

        public void setIgnoreVariablePattern​(Pattern pattern)
        Setter to define RegExp to ignore distance calculation for variables listed in this pattern.
        Parameters:
        pattern - a pattern.
      • setValidateBetweenScopes

        public void setValidateBetweenScopes​(boolean validateBetweenScopes)
        Setter to allow to calculate the distance between declaration of variable and its first usage in the different scopes.
        Parameters:
        validateBetweenScopes - Defines if allow to calculate distance between declaration of variable and its first usage in different scopes or not.
      • setIgnoreFinal

        public void setIgnoreFinal​(boolean ignoreFinal)
        Setter to allow to ignore variables with a 'final' modifier.
        Parameters:
        ignoreFinal - Defines if ignore variables with 'final' modifier or not.
      • 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
      • getInstanceName

        private static String getInstanceName​(DetailAST methodCallAst)
        Get name of instance whose method is called.
        Parameters:
        methodCallAst - DetailAST of METHOD_CALL.
        Returns:
        name of instance.
      • isInitializationSequence

        private static boolean isInitializationSequence​(DetailAST variableUsageAst,
                                                        String variableName)
        Processes statements until usage of variable to detect sequence of initialization methods.
        Parameters:
        variableUsageAst - DetailAST of expression that uses variable named variableName.
        variableName - name of considered variable.
        Returns:
        true if statements between declaration and usage of variable are initialization methods.
      • calculateDistanceInSingleScope

        private static Map.Entry<DetailAST,​IntegercalculateDistanceInSingleScope​(DetailAST semicolonAst,
                                                                                         DetailAST variableIdentAst)
        Calculates distance between declaration of variable and its first usage in single scope.
        Parameters:
        semicolonAst - Regular node of Ast which is checked for content of checking variable.
        variableIdentAst - Variable which distance is calculated for.
        Returns:
        entry which contains expression with variable usage and distance.
      • getDistToVariableUsageInChildNode

        private static int getDistToVariableUsageInChildNode​(DetailAST childNode,
                                                             DetailAST varIdent,
                                                             int currentDistToVarUsage)
        Returns the distance to variable usage for in the child node.
        Parameters:
        childNode - child node.
        varIdent - variable variable identifier.
        currentDistToVarUsage - current distance to the variable usage.
        Returns:
        the distance to variable usage for in the child node.
      • calculateDistanceBetweenScopes

        private static Map.Entry<DetailAST,​IntegercalculateDistanceBetweenScopes​(DetailAST ast,
                                                                                         DetailAST variable)
        Calculates distance between declaration of variable and its first usage in multiple scopes.
        Parameters:
        ast - Regular node of Ast which is checked for content of checking variable.
        variable - Variable which distance is calculated for.
        Returns:
        entry which contains expression with variable usage and distance.
      • searchVariableUsageExpressions

        private static Map.Entry<List<DetailAST>,​IntegersearchVariableUsageExpressions​(DetailAST variableAst,
                                                                                               DetailAST statementAst)
        Searches variable usages starting from specified statement.
        Parameters:
        variableAst - Variable that is used.
        statementAst - DetailAST to start searching from.
        Returns:
        entry which contains list with found expressions that use the variable and distance from specified statement to first found expression.
      • getFirstNodeInsideForWhileDoWhileBlocks

        private static DetailAST getFirstNodeInsideForWhileDoWhileBlocks​(DetailAST block,
                                                                         DetailAST variable)
        Gets first Ast node inside FOR, WHILE or DO-WHILE blocks if variable usage is met only inside the block (not in its declaration!).
        Parameters:
        block - Ast node represents FOR, WHILE or DO-WHILE block.
        variable - Variable which is checked for content in block.
        Returns:
        If variable usage is met only inside the block (not in its declaration!) then return the first Ast node of this block, otherwise - null.
      • getFirstNodeInsideIfBlock

        private static DetailAST getFirstNodeInsideIfBlock​(DetailAST block,
                                                           DetailAST variable)
        Gets first Ast node inside IF block if variable usage is met only inside the block (not in its declaration!).
        Parameters:
        block - Ast node represents IF block.
        variable - Variable which is checked for content in block.
        Returns:
        If variable usage is met only inside the block (not in its declaration!) then return the first Ast node of this block, otherwise - null.
      • getFirstNodeInsideSwitchBlock

        private static DetailAST getFirstNodeInsideSwitchBlock​(DetailAST block,
                                                               DetailAST variable)
        Gets first Ast node inside SWITCH block if variable usage is met only inside the block (not in its declaration!).
        Parameters:
        block - Ast node represents SWITCH block.
        variable - Variable which is checked for content in block.
        Returns:
        If variable usage is met only inside the block (not in its declaration!) then return the first Ast node of this block, otherwise - null.
      • getFirstCaseGroupOrSwitchRule

        private static DetailAST getFirstCaseGroupOrSwitchRule​(DetailAST block)
        Helper method for getFirstNodeInsideSwitchBlock to return the first CASE_GROUP or SWITCH_RULE ast.
        Parameters:
        block - the switch block to check.
        Returns:
        DetailAST of the first CASE_GROUP or SWITCH_RULE.
      • getFirstNodeInsideTryCatchFinallyBlocks

        private static DetailAST getFirstNodeInsideTryCatchFinallyBlocks​(DetailAST block,
                                                                         DetailAST variable)
        Gets first Ast node inside TRY-CATCH-FINALLY blocks if variable usage is met only inside the block (not in its declaration!).
        Parameters:
        block - Ast node represents TRY-CATCH-FINALLY block.
        variable - Variable which is checked for content in block.
        Returns:
        If variable usage is met only inside the block (not in its declaration!) then return the first Ast node of this block, otherwise - null.
      • isVariableInOperatorExpr

        private static boolean isVariableInOperatorExpr​(DetailAST operator,
                                                        DetailAST variable)
        Checks if variable is in operator declaration. For instance:
         boolean b = true;
         if (b) {...}
         
        Variable 'b' is in declaration of operator IF.
        Parameters:
        operator - Ast node which represents operator.
        variable - Variable which is checked for content in operator.
        Returns:
        true if operator contains variable in its declaration, otherwise - false.
      • isChild

        private static boolean isChild​(DetailAST parent,
                                       DetailAST ast)
        Checks if Ast node contains given element.
        Parameters:
        parent - Node of AST.
        ast - Ast element which is checked for content in Ast node.
        Returns:
        true if Ast element was found in Ast node, otherwise - false.
      • isVariableMatchesIgnorePattern

        private boolean isVariableMatchesIgnorePattern​(String variable)
        Checks if entrance variable is contained in ignored pattern.
        Parameters:
        variable - Variable which is checked for content in ignored pattern.
        Returns:
        true if variable was found, otherwise - false.