Converting an int to a binary with a fixed number of bits

Question

What is the easiest way in java to get the binary representation of an integer as a binary number with a fixed number of bits (For example, if I want to convert 3 with 5 bits, then the result would be 00011). In matlab, I can just specify the number of bits as an argument.

[Left padding a String with zeros](http://stackoverflow.com/questions/4469717/left-padding-a-string-with-zeros) might help solve this, along with `Integer.toBinaryString(int)`. — Obicere, Apr 02 '15 at 03:19

score 12 · Answer 1 · answered Apr 02 '15 at 03:40

12

This is a simple way:

String binaryString = Integer.toBinaryString(number);
binaryString = binaryString.substring(binaryString.length() - numBits);

Where number is the integer to convert and numBits is the fixed number of bits you are interested in.

answered Apr 02 '15 at 03:40

alfreema

1,308
14
26

But... I have "String index out of range: -3" in this case... – Line Jun 29 '17 at 13:41
Then you may want: binaryString = binaryString.substring(binaryString.length() - numBits >= 0 ? binaryString.length() - numBits : 0); – alfreema Jun 30 '17 at 02:56

SilentKnight · Answer 2 · 2015-04-02T03:48:59.177

9

If you want to convert an int into its binary representation, you need to do this:

String binaryIntInStr = Integer.toBinaryString(int);

If you want to get the bit count of an int, you need to do this:

int count = Integer.bitCount(int);

But you couldn't get the binary representation of an integer as a binary number with a fixed number of bits , for example, 7 has 3 bits, but you can't set its bit count 2 or 1. Because you won't get 7 from its binary representation with 2 or 1 bit count.

edited Apr 02 '15 at 03:48

answered Apr 02 '15 at 03:31

SilentKnight

13,761
19
49
78

The first line converts the binary integer to decimal and then parses it as binary. It if was correct it would do nothing, but it isn't correct. – user207421 Apr 02 '15 at 03:36
@EJP I have re-edit the answer, is it right now? – SilentKnight Apr 02 '15 at 03:49

score 3 · Answer 3 · edited Apr 05 '18 at 17:49

3

To convert n to numbOfBits of bits:

public static String intToBinary (int n, int numOfBits) {
   String binary = "";
   for(int i = 0; i < numOfBits; ++i, n/=2) {
      switch (n % 2) {
         case 0:
            binary = "0" + binary;
         break;
         case 1:
            binary = "1" + binary;
         break;
      }
   }

   return binary;
}

edited Apr 05 '18 at 17:49

hudsonb

2,214
19
20

answered Apr 02 '15 at 03:29

You forgot your **break;** statement in the code above. you'll add a 1 bit after every 0. – Phil Ives -Rain Everywhere Jun 26 '17 at 06:37

Converting an int to a binary with a fixed number of bits

3 Answers3

Linked