Barcode

package shoestore;

public class Barcode{
    private byte[] vonalkod;

    private Barcode(byte[] tomb){
        this.vonalkod = tomb;
    }

    private static boolean barCode_e(byte[] tomb){
        if(tomb.length == 13){
            for(byte a:tomb){
                if(a < 0 || a > 9){
                    return false;
                }
            }
            int szam =  0;
            int felsoKorlat = 0;
            for(int i = 0; i < 12; ++i){
                if((i+1) % 2 == 0){
                    szam += tomb[i]*3;
                }
                else{
                    szam += tomb[i];
                }
            }
            felsoKorlat = szam + (10 -(szam % 10));
            if(szam % 10 != 0){
                return felsoKorlat - szam == tomb[12];
            }
            return tomb[12] == 0;

        }
        return false;
    }
    public static Barcode create(byte[] tomb){
        if(barCode_e(tomb)){
            return new Barcode(tomb);
        }
        return null;
    }
    public static Barcode create(String s){
        if(s.length() == 13){
            char[] sv = s.toCharArray();;
            byte[] tomb = new byte[13];
            for(int i = 0; i < 13; ++i){
                if(!Character.isLetter(sv[i])){
                    tomb[i] = (byte)(Character.getNumericValue(sv[i]));
                }
                else{
                    return null;
                }
            }
            if(barCode_e(tomb)){
                return new Barcode(tomb);
            }
        }
        return null;
    }
}