Java: Selection sort of String array -

i working on sort algorithms school project , have problem . following code not sorting array,i have tried same code array of numbers(the change in if) , working string array , use of compareto not working puts items in "random" order.

public static void selectionsortisbn(book pin[], int bookscounter) {     (int x = 0; x < bookscounter; x++) {         int minindex = x;         (int y = x + 1; y < bookscounter; y++) {             if (pin[y].getisbn().compareto(pin[minindex].getisbn()) < 0) {                 minindex = y;             }         }         book temp = pin[x];         pin[x] = pin[minindex];         pin[minindex] = temp;     } } 

edit:

i changed inner :

        (int y = x + 1; y < bookscounter; y++) {             int com=pin[y].getisbn().compareto(pin[minindex].getisbn());             system.out.println(pin[y].getisbn()+"   "+pin[minindex].getisbn()+"  =   "+com);         } 

and output getting

1537   1485  =   1 596   1485  =   4 1164   1485  =   -3 909   1485  =   8 596   1537  =   4 1164   1537  =   -4 909   1537  =   8 1164   596  =   -4 909   596  =   4 909   1164  =   8 

this working correctly, mistake making expect "596" under "1485", when not, sorting them strings, 596 > 1485 ba > aaaaba. add leading zeroes if want compare numbers alphanumerically.