ArrayTrailingComma

Since Checkstyle 3.2

Description

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
}

Properties

name description type default value since
alwaysDemandTrailingComma Control whether to always check for a trailing comma, even when an array is inline. boolean false 8.33

Examples

To configure the check: 

<module name="Checker">
  <module name="TreeWalker">
    <module name="ArrayTrailingComma"/>
  </module>
</module>

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

Example of Usage

Violation Messages

All messages can be customized if the default message doesn't suit you. Please see the documentation to learn how to.

Package

com.puppycrawl.tools.checkstyle.checks.coding

Parent Module

TreeWalker