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# How to keep leading zeros when doing a parseInt

Rita Chakras
Greenhorn
Posts: 10
Hi,

I have a string which is a combination of a alpha prefix and a number suffix. I extract the prefix and get the number suffix of the string. Then, I do a Integer.parseInt on the suffix to get the value as an integer so that I can increment it. This works ok in general, but not when the suffix has leading zeros. In this case, I need to retain the leading zeros. So, for example, if the suffix is 001, when I parseInt it the integer value become 1 and then when I increment it, it becomes 2. I need it to be 001, 002.

Is there a way to do this?

Paul Clapham
Sheriff
Posts: 20966
31
After you increment it, convert it back to a String with those leading zeroes.

Rita Chakras
Greenhorn
Posts: 10
Problem is I'm not ever sure when the suffix has leading zeros. It depends on what value is being sent in. Also, the suffix may have 1 zeros to n number of zeros, but I don't know that. So I could have:
01, 02, 03 or I could have 08, 09, 10.

Paul Clapham
Sheriff
Posts: 20966
31
I think you mean you want the resulting String to be N characters, and you want to add leading zeroes until it reaches N characters, right? And you do know what N is, don't you?

Rita Chakras
Greenhorn
Posts: 10
Yes, I do know what N is (length of String), but I don't know if the N contains leading zeros or not, and if it does how many leading zeros. So if I increment, I don't know how many zeros I should add or when I should stop adding zeros.

I suppose I could parse through the string to figure out how many zeros it has and stop when it exceeds the length of N?

fred rosenberger
lowercase baba
Bartender
Posts: 12098
30
if you know the length of the original string, the length of the prefix, and the length of the incremented-then-converted-to-a-string integer part, you know how many zeros to add:

input string: prefix0000123
total length:13
prefix length: 6
length of string_after_increment (124): 3

13 - 6 - 3 = 4

Rob Spoor
Sheriff
Posts: 20512
54
If you use java.lang.DecimalFormat or String.format, you can specify the total number of digits. Whatever digits are not filled by the number itself are filled with zeros instead.

Ranch Hand
Posts: 733
4
Compute ix to get the number of leading 0's you want

String padded = ("0000000000000"+old).substring(ix); // get rightmost chars

Campbell Ritchie
Sheriff
Posts: 48652
56
Apart from the fact that String.format won't work on beginners':

int i = . . .;
String numberText = String.format("%010d", i);

Rita Chakras
Greenhorn
Posts: 10
Thanks so much for all your help. Fred's solution works well.