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

      • alwaysDemandTrailingComma

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