How to make two char rows alternate in order to make a rectangle JAVA

Question

My code takes 2 input numbers to create the rows and columns of a rectangle. In that rectangle, the user chooses 2 letters for the rectangle body but they have to alternate, like this: (without the dashes ofc)

-xxxxx
-r r r r r
-xxxxx
-r r r r r

Whenever I try to make them alternate, the rows usually end up like "xrxrx" or "xrrrr" instead of a single letter. I've tried adding them "filler.append(firstLetter + secLetter);" but it just results in numbers. This probably has a really easy solution but I just don't see it ha ha...(・_・;) Any hints would be greatly appreciated, thank you!

public static void recDraw ( int rows, int columns, char firstLetter, char secLetter){
        StringBuilder filler = new StringBuilder();
        for (int i = 0; i < rows; i++) {
            for (int j = 0; j < columns; j++) {
                filler.append(firstLetter);
                filler.append(secLetter);
            }
            filler.append('\n');
        }
        System.out.println(filler);
    }

Answer 1

Inside inner loop (with counter j), before appending the letter to StringBuilder filler, check whether it is Fistletter line or SecondLetter line by using modulus operation on i value. 'i' value is used because it represents the line/row.

public static void recDraw ( int rows, int columns, char firstLetter, char secLetter){
    StringBuilder filler = new StringBuilder();
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < columns; j++) {
            if(i%2 == 0){
                filler.append(firstLetter);
            } else{
                filler.append(secLetter);
            }
        }
        filler.append('\n');
    }
    System.out.println(filler);
}