Filling a Multidimensional Array using a Stream

Question

I'm new to Java 8 and currently failing to grasp Streams fully, is it possible to fill an array using the Stream functional operations? This is an example code of how I would do it with a standard for loop:

public static void testForLoop(){
    String[][] array = new String[3][3];
    for (int x = 0; x < array.length; x++){
        for (int y = 0; y < array[x].length; y++){
            array[x][y] = String.format("%c%c", letter(x), letter(y));
        }
    }               
}

public static char letter(int i){
    return letters.charAt(i);
} 

If it is possible how would I do it using Stream? If it is possible, is it convenient (performance and readability wise)?

Answer 1

Here you have a solution that produces the array instead of modifying a previously defined variable:

String[][] array = 
    IntStream.range(0, 3)
             .mapToObj(x -> IntStream.range(0, 3)
                                     .mapToObj(y -> String.format("%c%c", letter(x), letter(y)))
                                     .toArray(String[]::new))
             .toArray(String[][]::new);

If you want to use parallel streams then it's very important to avoid side effects like modifications of a variable (array or object). It might lead to race conditions or other concurrency issues. You can read more about that in java.util.stream package documentation - see Non-interference, Stateless behaviors and Side-effects sections.