Package com.puppycrawl.tools.checkstyle.checks.blocks

Class EmptyBlockCheck

java.lang.Object
com.puppycrawl.tools.checkstyle.api.AutomaticBean
com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter
com.puppycrawl.tools.checkstyle.api.AbstractCheck
com.puppycrawl.tools.checkstyle.checks.blocks.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

  • Field Details

    • MSG_KEY_BLOCK_NO_STATEMENT

      public static final String MSG_KEY_BLOCK_NO_STATEMENT
      A key is pointing to the warning message text in "messages.properties" file.
      See Also:

    • MSG_KEY_BLOCK_EMPTY

      public static final String MSG_KEY_BLOCK_EMPTY
      A key is pointing to the warning message text in "messages.properties" file.
      See Also:

    • option

      private BlockOption option
      Specify the policy on block contents.

  • Constructor Details

    • EmptyBlockCheck

      public EmptyBlockCheck()

  • Method Details

    • 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

    • 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:

    • 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:

    • 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:

    • 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

    • 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 static boolean checkIsAllLinesAreWhitespace(String[] lines, int lineFrom, int lineTo)
      Checks is all lines in array contain whitespaces only.
      Parameters:
      lines - array of lines
      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