Class EmptyBlockCheck

  • All Implemented Interfaces:
    Configurable, Contextualizable

    public class EmptyBlockCheck
    extends AbstractCheck

    Checks for empty blocks. This check does not validate sequential blocks.

    Sequential blocks won't be checked. Also, no violations for fallthrough:

     switch (a) {
       case 1:                          // no violation
       case 2:                          // no violation
       case 3: someMethod(); { }        // no violation
       default: break;
     }
     

    NOTE: This check processes LITERAL_CASE and LITERAL_DEFAULT separately. Verification empty block is done for single most nearest case or default.

    To configure the check:

     <module name="EmptyBlock"/>
     

    Example:

     public class Test {
       private void emptyLoop() {
         for (int i = 0; i < 10; i++) { // violation
         }
    
         try { // violation
    
         } catch (Exception e) {
           // ignored
         }
       }
     }
     

    To configure the check for the text policy and only try blocks:

     <module name="EmptyBlock">
       <property name="option" value="text"/>
       <property name="tokens" value="LITERAL_TRY"/>
     </module>
     

    Example:

     public class Test {
       private void emptyLoop() {
         for (int i = 0; i < 10; i++) {
           // ignored
         }
    
         // violation on next line
         try {
    
         } catch (Exception e) {
           // ignored
         }
       }
     }
     

    To configure the check for default in switch block:

     <module name="EmptyBlock">
       <property name="tokens" value="LITERAL_DEFAULT"/>
     </module>
     

    Example:

     public class Test {
       private void test(int a) {
         switch (a) {
           case 1: someMethod();
           default: // OK, as there is no block
         }
         switch (a) {
           case 1: someMethod();
           default: {} // violation
         }
       }
     }
     

    Parent is com.puppycrawl.tools.checkstyle.TreeWalker

    Violation Message Keys:

    • block.empty
    • block.noStatement
    Since:
    3.0
    • Method Detail

      • setOption

        public void setOption​(String optionStr)
        Setter to specify the policy on block contents.
        Parameters:
        optionStr - string to decode option from
        Throws:
        IllegalArgumentException - if unable to decode
      • 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
      • hasText

        private boolean hasText​(DetailAST slistAST)
        Checks if SLIST token contains any text.
        Parameters:
        slistAST - a DetailAST value
        Returns:
        whether the SLIST token contains any text.
      • checkIsAllLinesAreWhitespace

        private boolean checkIsAllLinesAreWhitespace​(int lineFrom,
                                                     int lineTo)
        Checks is all lines from 'lineFrom' to 'lineTo' (exclusive) contain whitespaces only.
        Parameters:
        lineFrom - check from this line number
        lineTo - check to this line numbers
        Returns:
        true if lines contain only whitespaces
      • findLeftCurly

        private static DetailAST findLeftCurly​(DetailAST ast)
        Calculates the left curly corresponding to the block to be checked.
        Parameters:
        ast - a DetailAST value
        Returns:
        the left curly corresponding to the block to be checked