Class ModifiedControlVariableCheck

  • All Implemented Interfaces:
    Configurable, Contextualizable

    public final class ModifiedControlVariableCheck
    extends AbstractCheck

    Checks that for loop control variables are not modified inside the for block. An example is:

     for (int i = 0; i < 1; i++) {
       i++; // violation

    Rationale: If the control variable is modified inside the loop body, the program flow becomes more difficult to follow. See FOR statement specification for more details.

    Such loop would be suppressed:

     for (int i = 0; i < 10;) {

    NOTE:The check works with only primitive type variables. The check will not work for arrays used as control variable.An example is

     for (int a[]={0};a[0] < 10;a[0]++) {
      a[0]++;   // it will skip this violation
    • Property skipEnhancedForLoopVariable - Control whether to check enhanced for-loop variable. Type is boolean. Default value is false.

    To configure the check:

     <module name="ModifiedControlVariable"/>


     for(int i=0;i < 8;i++) {
       i++; // violation, control variable modified
     String args1[]={"Coding", "block"};
     for (String arg: args1) {
       arg = arg.trim(); // violation, control variable modified

    By default, This Check validates Enhanced For-Loop.

    Option 'skipEnhancedForLoopVariable' could be used to skip check of variable from Enhanced For Loop.

    An example of how to configure the check so that it skips enhanced For Loop Variable is:

     <module name="ModifiedControlVariable">
       <property name="skipEnhancedForLoopVariable" value="true"/>


     for(int i=0;i < 8;i++) {
       i++; // violation, control variable modified
     String args1[]={"Coding", "block"};
     for (String arg: args1) {
       arg = arg.trim(); // ok

    Parent is

    Violation Message Keys:

    • modified.control.variable
    • Method Detail

      • setSkipEnhancedForLoopVariable

        public void setSkipEnhancedForLoopVariable​(boolean skipEnhancedForLoopVariable)
        Setter to control whether to check enhanced for-loop variable.
        skipEnhancedForLoopVariable - whether to skip enhanced for-loop variable
      • 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
        the token set this check is designed for.
        See Also:
      • beginTree

        public void beginTree​(DetailAST rootAST)
        Description copied from class: AbstractCheck
        Called before the starting to process a tree. Ideal place to initialize information that is to be collected whilst processing a tree.
        beginTree in class AbstractCheck
        rootAST - the root of the tree
      • enterBlock

        private void enterBlock()
        Enters an inner class, which requires a new variable set.
      • exitBlock

        private void exitBlock()
        Leave an inner class, so restore variable set.
      • checkIdent

        private void checkIdent​(DetailAST ast)
        Check if ident is parameter.
        ast - ident to check.
      • leaveForIter

        private void leaveForIter​(DetailAST ast)
        Push current variables to the stack.
        ast - a for definition.
      • getVariablesManagedByForLoop

        private static Set<StringgetVariablesManagedByForLoop​(DetailAST ast)
        Determines which variable are specific to for loop and should not be change by inner loop body.
        ast - For Loop
        Set of Variable Name which are managed by for
      • leaveForEach

        private void leaveForEach​(DetailAST paramDef)
        Push current variables to the stack.
        paramDef - a for-each clause variable
      • leaveForDef

        private void leaveForDef​(DetailAST ast)
        Pops the variables from the stack.
        ast - a for definition.
      • popCurrentVariables

        private void popCurrentVariables​(int count)
        Pops given number of variables from currentVariables.
        count - Count of variables to be popped from currentVariables
      • getForInitVariables

        private static Set<StringgetForInitVariables​(DetailAST ast)
        Get all variables initialized In init part of for loop.
        ast - for loop token
        set of variables initialized in for loop
      • getForIteratorVariables

        private static Set<StringgetForIteratorVariables​(DetailAST ast)
        Get all variables which for loop iterating part change in every loop.
        ast - for loop literal(TokenTypes.LITERAL_FOR)
        names of variables change in iterating part of for