Package com.puppycrawl.tools.checkstyle.checks.coding

Class ArrayTrailingCommaCheck

  • All Implemented Interfaces:
    Configurable, Contextualizable
    public class ArrayTrailingCommaCheck
extends AbstractCheck

    Checks that array initialization contains a trailing comma. 

     int[] a = new int[]
 {
   1,
   2,
   3,
 };

    By default, the check demands a comma at the end if neither left nor right curly braces are on the same line as the last element of the array. 

     return new int[] { 0 };
 return new int[] { 0
   };
 return new int[] {
   0 };

    Rationale: Putting this comma in makes it easier to change the order of the elements or add new elements on the end. Main benefit of a trailing comma is that when you add new entry to an array, no surrounding lines are changed. 

     {
   100000000000000000000,
   200000000000000000000, // OK
 }

 {
   100000000000000000000,
   200000000000000000000,
   300000000000000000000,  // Just this line added, no other changes
 }

    If closing brace is on the same line as trailing comma, this benefit is gone (as the check does not demand a certain location of curly braces the following two cases will not produce a violation): 

     {100000000000000000000,
  200000000000000000000,} // Trailing comma not needed, line needs to be modified anyway

 {100000000000000000000,
  200000000000000000000, // Modified line
  300000000000000000000,} // Added line

    If opening brace is on the same line as trailing comma there's also (more arguable) problem: 

     {100000000000000000000, // Line cannot be just duplicated to slightly modify entry
 }

 {100000000000000000000,
  100000000000000000001, // More work needed to duplicate
 }
    • Property alwaysDemandTrailingComma - Control whether to always check for a trailing comma, even when an array is inline. Type is boolean. Default value is false.

    To configure the check: 

     <module name="ArrayTrailingComma"/>

    Which results in the following violations: 

     int[] numbers = {1, 2, 3};        //no violation
 boolean[] bools = {
 true,
 true,
 false
 };        //violation

 String[][] text = {{},{},};        //no violation

 double[][] decimals = {
 {0.5, 2.3, 1.1,},        //no violation
 {1.7, 1.9, 0.6},
 {0.8, 7.4, 6.5}
 };        // violation as previous line misses a comma

 char[] chars = {'a', 'b', 'c'
   };        / /no violation

 String[] letters = {
   "a", "b", "c"};        // no violation

 int[] a1 = new int[]{
   1,
   2
   ,
 };        // no violation

 int[] a2 = new int[]{
   1,
   2
   ,};        // no violation

    To configure check to always validate trailing comma:

     <module name="ArrayTrailingComma">
   <property name="alwaysDemandTrailingComma" value="true"/>
 </module>

    Example:

     int[] numbers = {1, 2, 3}; // violation
 boolean[] bools = {
 true,
 true,
 false // violation
 };

 String[][] text = {{},{},}; // OK

 double[][] decimals = {
 {0.5, 2.3, 1.1,}, // OK
 {1.7, 1.9, 0.6}, // violation
 {0.8, 7.4, 6.5} // violation
 }; // violation, previous line misses a comma

 char[] chars = {'a', 'b', 'c'  // violation
   };

 String[] letters = {
   "a", "b", "c"}; // violation

 int[] a1 = new int[]{
   1,
   2
   ,
 }; // OK

 int[] a2 = new int[]{
   1,
   2
   ,}; // OK

    Parent is com.puppycrawl.tools.checkstyle.TreeWalker

    Violation Message Keys:

    • array.trailing.comma
    Since:
    3.2

    • Field Detail

      • MSG_KEY

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

    • Constructor Detail

      • ArrayTrailingCommaCheck

        public ArrayTrailingCommaCheck()

    • Method Detail

      • setAlwaysDemandTrailingComma

        public void setAlwaysDemandTrailingComma​(boolean alwaysDemandTrailingComma)
        Setter to control whether to always check for a trailing comma, even when an array is inline.
        Parameters:
        alwaysDemandTrailingComma - whether to always check for a trailing comma.

      • 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:
        TokenTypes

      • 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

      • 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:
        TokenTypes

      • visitToken

        public void visitToken​(DetailAST arrayInit)
        Description copied from class: AbstractCheck
        Called to process a token.
        Overrides:
        visitToken in class AbstractCheck
        Parameters:
        arrayInit - the token to process