Java Glossary : hexadecimal

Last updated 2004-06-29 by Roedy Green ©1996-2004 Canadian Mind Products

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hexadecimal

or hex for short, base 16 numbers, e.g. 08Cf, made of the digits 0..9 and a..f. This is the number system we would have used had we sixteen fingers instead of ten. You can display in hex using code like this:

String hex = Integer.toString(i , 16 /* radix */ );

That won't apply any lead zeroes. Here is how to get a lead 0 for a fixed two character hex representation of a byte:

// convert a byte b to 2-char hex string
// with possible leading zero.
String s2 = Integer.toString( ( b & 0xff ) + 0x100, 16 /* radix */ ).substring( 1 );

You can convert a hex String to internal binary like this:

int i = Integer.parseInt(g.trim(), 16 /* radix */ );

The following code looks more complicated, but is considerably faster. It also handles a byte array, not just a single byte.

// Fast convert a byte array to a hex string
// with possible leading zero.

public static String toHexString ( byte[] b )
   {
   StringBuffer sb = new StringBuffer( b.length * 2 );
   for ( int i=0; i<b.length; i++ )
      {
      // look up high nibble char
      sb.append( hexChar [( b[i] & 0xf0 ) >>> 4] );

      // look up low nibble char
      sb.append( hexChar [b[i] & 0x0f] );
      }
   return sb.toString();
   }

// table to convert a nibble to a hex char.
static char[] hexChar = {
   '0' , '1' , '2' , '3' ,
   '4' , '5' , '6' , '7' ,
   '8' , '9' , 'a' , 'b' ,
   'c' , 'd' , 'e' , 'f'};

And here is how to go the other way from a hex string back to a byte array:

view

Since the computer uses binary internally, it makes no sense to talk about converting an int from hex to decimal or back, only a String.

In Java you can use hex literals like this

int a = 0x8cf;

The computer chip works internally in binary (base 2 numbers), with numbers made only of the digits 0 and 1, low voltage/high voltage. Binary numbers are somewhat bulky to write out, so they are usually written in base 16, hex. It is very easy to convert hex to binary and visa versa using the following table. For example, the hex number 8cf is 100011001111 in binary. Converting between decimal and hex is more difficult. You must do successive divisions and moduluses by 10 or 16.

Decimal	Hex	Binary
0	0	0000
1	1	0001
2	2	0010
3	3	0011
4	4	0100
5	5	0101
6	6	0110
7	7	0111
8	8	1000
9	9	1001
10	a	1010
11	b	1011
12	c	1100
13	d	1101
14	e	1110
15	f	1111

binary formats ¤ binary ¤ conversion ¤ Hex Editors ¤ HexView: allows you to view files in hex ¤ Learn To Count Applet to sharpen your intuition on how binary, hex, and octol work ¤ literals ¤ masking ¤ octal ¤ PGP hex encoding as words ¤ radix ¤ SlickEdit: allows you to view files in hex

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