Binary Representation of integers

[kev neibarger]

I'm recently studying for the java 2 cert from sun and I keep coming across a question like this:

public class Bitwise2 {
 
   public static void main(String[] args) {
     int x = 12 & 13;
     int y = x ^ 6;
     System.out.println(y | 3);
   }
 
}

The question is, what is the printed result. My question is this, is there a quick way to convert numbers to their binary representations such as 12 = 1100 and 13 = 1101. This is really the only thing I haven't been able to find an answer to. I'd like to know a quick way so I don't spend 1/2 hour on one question trying to calculate a binary representation of a number.

Thanks!
Kevin


[HENRY: Added code tags]
[ October 24, 2006: Message edited by: Henry Wong ]

[Jesper de Jong]

Well, what's your current method that takes you so much time to convert a number to its binary form? For small numbers like 3, 6, 12, 13 it isn't very difficult.

Just look at what values the different bits represent. For example, if I have an 8-bit number, the values of the bits from left to right are:

2^7 / 2^6 / 2^5 / 2^4 / 2^3 / 2^2 / 2^1 / 2^0 = 128 / 64 / 32 / 16 / 8 / 4 / 2 / 1

To convert a number to binary, you just write it as a sum of the numbers above, and that gives you your "1" bits. For example:

3 = 2 + 1 = 00000011
6 = 4 + 2 = 00000110
12 = 8 + 4 = 00001100
13 = 8 + 4 + 1 = 00001101
79 = 64 + 8 + 4 + 2 + 1 = 01001111

[marc weber]

Welcome to JavaRanch!

I draw a simple table, then fill in 0's and 1's from left to right. For example, adding 83 and 10 in binary...

...  128  |  64  |  32  |  16  |  8  |  4  |  2  |  1  |
=================================================================
       0  |   1  |   0  |   1  |  0  |  0  |  1  |  1  | = 83
       0  |   0  |   0  |   0  |  1  |  0  |  1  |  0  | = 10
_________________________________________________________________
       0  |   1  |   0  |   1  |  1  |  1  |  0  |  1  | = 93

Since this is an SCJP question, I'm moving this to our SCJP forum. Please continue this discussion there.
[ October 24, 2006: Message edited by: marc weber ]

[samir Sadiki]

...or you could use the method:

Integer.toBinaryString(int i)

Returns a string representation of the integer argument as an unsigned integer in base 2.

[marc weber]

Originally posted by samir Sadiki:
...or you could use the method...

Well, when you're actually sitting for the exam, limited to whatever writing tools the testing center provides...
[ October 24, 2006: Message edited by: marc weber ]