Package com.puppycrawl.tools.checkstyle.checks.sizes

Class LambdaBodyLengthCheck

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.sizes.LambdaBodyLengthCheck
All Implemented Interfaces:
Configurable, Contextualizable
public class LambdaBodyLengthCheck extends AbstractCheck

Checks lambda body length.

Rationale: Similar to anonymous inner classes, if lambda body becomes very long it is hard to understand and to see the flow of the method where the lambda is defined. Therefore long lambda body should usually be extracted to method.

  • Property max - Specify the maximum number of lines allowed. Type is int. Default value is 10.

To configure the check to accept lambda bodies with up to 10 lines: 

 <module name="LambdaBodyLength"/>

Example: 

 class Test {
   Runnable r = () -> { // violation, 11 lines
       System.out.println(2); // line 2 of lambda
       System.out.println(3);
       System.out.println(4);
       System.out.println(5);
       System.out.println(6);
       System.out.println(7);
       System.out.println(8);
       System.out.println(9);
       System.out.println(10);
   }; // line 11

   Runnable r2 = () -> // violation, 11 lines
       "someString".concat("1") // line 1 of lambda
                   .concat("2")
                   .concat("3")
                   .concat("4")
                   .concat("5")
                   .concat("6")
                   .concat("7")
                   .concat("8")
                   .concat("9")
                   .concat("10")
                   .concat("11"); // line 11

   Runnable r3 = () -> { // ok, 10 lines
       System.out.println(2); // line 2 of lambda
       System.out.println(3);
       System.out.println(4);
       System.out.println(5);
       System.out.println(6);
       System.out.println(7);
       System.out.println(8);
       System.out.println(9);
   }; // line 10
 }

To configure the check to accept lambda bodies with max 5 lines: 

 <module name="LambdaBodyLength">
   <property name="max" value="5"/>
 </module>

Example: 

 class Test {
   Runnable r = () -> { // violation, 6 lines
       System.out.println(2); // line 2 of lambda
       System.out.println(3);
       System.out.println(4);
       System.out.println(5);
   };

   Runnable r2 = () -> // violation, 6 lines
       "someString".concat("1")
                   .concat("2")
                   .concat("3")
                   .concat("4")
                   .concat("5")
                   .concat("6");

   Runnable r3 = () -> { // ok, 5 lines
       System.out.println(2);
       System.out.println(3);
       System.out.println(4);
   };
 }

Parent is com.puppycrawl.tools.checkstyle.TreeWalker

Violation Message Keys:

  • maxLen.lambdaBody
Since:
8.37

  • Field Details

    • MSG_KEY

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

    • DEFAULT_MAX

      private static final int DEFAULT_MAX
      Default maximum number of lines.
      See Also:

    • max

      private int max
      Specify the maximum number of lines allowed.

  • Constructor Details

    • LambdaBodyLengthCheck

      public LambdaBodyLengthCheck()

  • Method Details

    • setMax

      public void setMax(int length)
      Setter to specify the maximum number of lines allowed.
      Parameters:
      length - the maximum length of lambda body.

    • 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

    • getLength

      private static int getLength(DetailAST ast)
      Get length of lambda body.
      Parameters:
      ast - lambda body node.
      Returns:
      length of lambda body.

    • getLastNodeLineNumber

      private static int getLastNodeLineNumber(DetailAST lambdaBody)
      Get last child node in the tree line number.
      Parameters:
      lambdaBody - lambda body node.
      Returns:
      last child node in the tree line number.

    • getFirstNodeLineNumber

      private static int getFirstNodeLineNumber(DetailAST lambdaBody)
      Get first child node in the tree line number.
      Parameters:
      lambdaBody - lambda body node.
      Returns:
      first child node in the tree line number.