Class ArrayTrailingCommaCheck

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.coding.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 Details

    • MSG_KEY

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

    • alwaysDemandTrailingComma

      private boolean alwaysDemandTrailingComma
      Control whether to always check for a trailing comma, even when an array is inline.

  • Constructor Details

    • ArrayTrailingCommaCheck

      public ArrayTrailingCommaCheck()

  • Method Details

    • 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:

    • 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 arrayInit)
      Description copied from class: AbstractCheck
      Called to process a token.
      Overrides:
      visitToken in class AbstractCheck
      Parameters:
      arrayInit - the token to process