aspose file tools*
The moose likes Programmer Certification (SCJP/OCPJP) and the fly likes two's complement Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login
JavaRanch » Java Forums » Certification » Programmer Certification (SCJP/OCPJP)
Bookmark "two Watch "two New topic
Author

two's complement

suresh kamsa
Ranch Hand

Joined: Jul 30, 2001
Posts: 149
1. byte b1 = (byte)(2 * Byte.MAX_VALUE);
I think b1 = 0111 1111 1111 1111 1111 1111 1111 1111
2.byte b2 = -2;
for negtive number
1000 0000 0000 0000 0000 0000 0000 0000
binary of 2 is 10
which is equal to
1000 0000 0000 0000 0000 0000 0000 0010 if I invert also because of negtive we should get
0111 1111 1111 1111 1111 1111 1111 1101
How is (b1 == b2).Did I do anything wrong?
Thanks.
Kavitha Chandrasekaran
Ranch Hand

Joined: Jul 24, 2002
Posts: 34
Hi,
b1 will be 11111110 and because it is a byte, it has 8 bits with the most significant bit as 1(that makes it negative). When you do the conversion to decimal,the value is -2.
So, b1 == b2 is true.
Kavitha
Ron Newman
Ranch Hand

Joined: Jun 06, 2002
Posts: 1056
A byte is only 8 bits, not 32 as you are showing here.


Ron Newman - SCJP 1.2 (100%, 7 August 2002)
suresh kamsa
Ranch Hand

Joined: Jul 30, 2001
Posts: 149
1. byte b1 = (byte)(2 * Byte.MAX_VALUE);
2. byte b2 = -2;
3. System.out.println(b1 == b2);
as per my knowledge MAX_VALUE = 0111 ... 1111
according to that b1 = 0111 1111(most significant seven bits set to 1 and least one bit set to zero)
MIN_VALUE = 1000 ... 0000
how b1 becomes -2 here, please explain me in detail.
Valentin Crettaz
Gold Digger
Sheriff

Joined: Aug 26, 2001
Posts: 7610
As you said Byte.MAX_VALUE is 01111111. Now, when you multiply a number by 2, what happens is a shift left by one bit. So,
Byte.MAX_VALUE * 2
can be resolved to
01111111 << 1
which gives
11111110
whose value is -2.
To be sure, let's take the byte value 2 and make it negative (keyword: 2's complement):
2 is 00000010
to get -2 we invert all bits like this
11111101
and add 1, that is
11111110
As you can see we get the same value...
So Byte.MAX_VALUE * 2 is equal to -2


SCJP 5, SCJD, SCBCD, SCWCD, SCDJWS, IBM XML
[Blog] [Blogroll] [My Reviews] My Linked In
suresh kamsa
Ranch Hand

Joined: Jul 30, 2001
Posts: 149
Thanks for your in-detail explanation.
Is the same rule applies wheh I multiply number by 3 or 4 etc.(shift left by one bit)
eg.(Byte.MAX_VALUE * 3)
Is the same rule applies to Short.MAXVALUE,Integer.MAXVALUE etc. If anybody has a chart kind which shows this please pass on to me.
What about Byte.MINVALUE,Short.MINVALUE,Integer.MINVALUE etc
Is this possible only for Wrapper primitives?
Thanks
 
It is sorta covered in the JavaRanch Style Guide.
 
subject: two's complement