Question

I have a byte array that can be of size 2,3 or 4. I need to convert this to the correct integer value. I also need to do this in reverse, i.e an 2,3 or 4 character integer to a byte array.

e.g., raw hex bytes are : 54 and 49. The decoded string US-ASCII value is 61. So the integer answer needs to be 61.

I have read all the conversion questions on stackoverflow etc that I could find, but they all give the completely wrong answer, I dont know whether it could be the encoding?

If I do new String(lne,"US-ASCII"), where lne is my byte array, I get the correct 61. But when doing this ((int)lne[0] << 8) | ((int)lne[1] & 0xFF), I get the complete wrong answer.

This may be a silly mistake or I completely don’t understand the number representation schemes in Java and the encoding/decoding idea.

Any help would be appreciated.

NOTE: I know I can just parse the String to integer, but I would like to know if there is a way to use fast operations like shifting and binary arithmetic instead?

Answer 1

You need two conversion steps. First, convert your ascii bytes to a string. That’s what new String(lne,"us-ascii") does for you. Then, convert the string representation of the number to an actual number. For that you use something like Integer.parseInt(theString) — remember to handle NumberFormatException.