Arrays with trailing commas inside an array initializer in Java

Question

Array initializers can be used to initialize arrays at compile-time. An initializer with trailing commas as shown below compiles fine.

int a[][] = {{1,2,} ,{3,4,} , {5,6,},}; //Trailing commas cause no compiler error  for(int i=0;i<a.length;i++) {     for(int j=0;j<2;j++)     {         System.out.print(a[i][j]+"\t");     }     System.out.println(); } 

Output :

1        2         3        4         5        6      

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Also legal with one dimension arrays as obvious with the above discussion.

int[] b = {1, 2, 3, 4, 5, 6,}; //A trailing comma causes no compiler error  for(int i=0;i<b.length;i++) {     System.out.print(b[i]+"\t"); } 

Output :

1        2        3        4        5        6 

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Even the following is a legal syntax and compiles fine.

int c[][] = {{,} ,{,} , {,},};  

The compiler should expect a constant value (or another initializer) after and before a comma ,. How is this compiled? Does the compiler simply ignore such commas or something else happens in such a scenario?

Answer 1

The trailing comma is ignored. From the Java specification:

A trailing comma may appear after the last expression in an array initializer and is ignored.