Smartly Decoding Hex Input (e.g 0x32, 0x3, 32 etc...)

Question

I seem to be going around in circles with this one... There are many methods to achieve this and I could use a few if statements like I've done int he example below, but I want a smarter method.

Problem

The user is asked to input a value in hex, the program grabs this string and will now want to convert it into an integer, bearing in mind this is a hex value. The input could be for example:

0x00 0xf ff 2

My Attempt

String hexString = response.getResult(); //grabs the user input

int hexInt = Integer.decode(hexString); //Doesn't work if the user doesn't add "0x" at the start

String regex = "\\s*\\b0x\\b\\s*";
String hexInt = hexString.replaceAll(regex, ""); //Doesn't like 0x for some reason

Int hexInt = Integer.valueOf(hexString,16); //Doesn't like 0x

Any ideas on how to do this smartly?

http://stackoverflow.com/questions/5886619/hexadecimal-to-integer-in-java#5886656 — Jamey, Apr 08 '14 at 12:48
"I could use a few if statements like I've done int he example below" - your sample code doesn't include any `if` statements. — Jon Skeet, Apr 08 '14 at 12:49
Sorry it didn't, I meant to. I have the answer I need now though — fiz, Apr 08 '14 at 13:04

score 2 · Accepted Answer · answered Apr 08 '14 at 12:48

2

Why not just remove 0x if the string starts with it? There's no need to use a regular expression for this - just a combination of startsWith and substring is simpler to understand (IMO):

String hexString = response.getResult();
if (hexString.startsWith("0x")) {
    hexString = hexString.substring(2);
}
int value = Integer.parseInt(hexString, 16);

answered Apr 08 '14 at 12:48

Jon Skeet

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Maybe a bit shorter: `int value = Integer.parseInt(hexString.replace("0x", ""), 16);` or better with the if? – ifloop Apr 08 '14 at 12:52
1

@ifLoop: That would accept "50x5" whereas I'd expect that to be an error. – Jon Skeet Apr 08 '14 at 12:56
Didn't think of that. Convinced me! – ifloop Apr 08 '14 at 12:57

Smartly Decoding Hex Input (e.g 0x32, 0x3, 32 etc...)

Problem

My Attempt

1 Answers1