public static final char alphabet[] = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'};


 public static char defLettre(int j) {
        char result = alphabet[j];

        return result;

    }

    public static void runThis(int n) {

        for (int l = 1; l <= 2 * n - 1; l++) {
            System.out.println("\n");
            for (int c = 1; c <= 2 * n - 1; c++) {
                boolean match = false;
                for (int j = 1; j < 2 * n; j++) {
                    if ((l == 1) || (l == 2 * n - j) || (c == 1) || (c == 2 * n - j)) {
                        if (j == 1) {
                            System.out.print('a');
                        } else {
                            System.out.print(defLettre(j - 1));
                        }
                        match = true;
                        break;

                    }

                }

            }

        }

    }
}


J'obtiens ça :

aaaaaaa

afedcba

aeedcba

adddcba

accccba

abbbbba

aaaaaaa

Je veux obtenir ça :

aaaaaaa
abbbbba
abcccba
abcdcba
abcccba
abbbbba
aaaaaaa