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apoorba mohapatra
Greenhorn

Joined: Mar 28, 2005
Posts: 7
Question 15
-----------
class JJF5 {
public static void main(String args[]) {
System.out.print(Integer.toHexString(Integer.MIN_VALUE)+",");
System.out.print(Integer.toHexString(Integer.MAX_VALUE));
}}

from [http://www.danchisholm.net/dec20/guide/chapter2/exam1.html]

How should I calculate the output?
Int has min value -2^ 31.
So do we need to convert that value to hexadecimal form and get the output?
But calculating this stuff would be very lengthy.

BTW the answer is: Prints: 80000000,7fffffff
Chandrakanth
Ranch Hand

Joined: Aug 16, 2005
Posts: 60
System.out.print(Integer.toHexString(Integer.MIN_VALUE)+",");
System.out.print(Integer.toHexString(Integer.MAX_VALUE));

Int is 32bits (with 1 sign bit)
so Min value of int(which is -ve) in its hex representation is
for -ve sign bit is 1
for +ve sign bit is 0

Sign Bit + 31 zeros
1 000 0000 0000 0000 0000 0000 0000 0000 [min value of int]
so output is: 80000000

Max Value is +ve
Sign Bit + 31 1's
0 111 1111 1111 1111 1111 1111 1111 1111
so output is: 7fffffff
Enge Chall
Ranch Hand

Joined: Nov 22, 2005
Posts: 30
Hi Apoorba, further to make it simple to face simillar questions you must be familliar with one's complement and two's complement in your studies.
It goes like this:
'-' ve numbers are represented in 2's complement form in computer memory.
What is 2's complement form ? Ans: It's one's complement + 1 ie add 1 to one's complement.
What is one's complement ? Ans: Just alter the digits of your binary numbers. ( if 1 make it 0, if 0 make it 1 ).

How -1 is represented ? Ans: It's 1 with a -ve sign ie two's complement of +1 with a -ve sign.
What is -ve sign and +ve sign ? Ans: The MSB is switched on ( ie MSB is 1 for -ve ), MSB is switched off( ie MSB is 0 for +ve ).

What is MSB ? Ans: The left most bit called Most Significant Bit .

==> let's eg: find out how -1 is stored in computer <==
So keeping that in mind now find out the 2's complement of 1. As java int is 4 bytes ie 32 bits, the 32nd bit is the MSB.

Now let's calculate:
+1 is 0000 0000 0000 0000 0000 0000 0000 0001
-1 is 2's complement of +1 ie 1's complement of +1 added by 1 as below :
1111 1111 1111 1111 1111 1111 1111 1110 +
0000 0000 0000 0000 0000 0000 0000 0001
---------------------------------------
1111 1111 1111 1111 1111 1111 1111 1111 ( See here MSB is switched on automatically for -ve )

Now coming to your question ie -2^31 is the minimum -ve value of int in java ( I am sure , you know how ? )

Now let's calculate:
+2^31 is 1000 0000 0000 0000 0000 0000 0000 0000
-2^31 is 2's complement of +2^31 ie 1's complement of +2^31 added by 1 as below :
0111 1111 1111 1111 1111 1111 1111 1111 +
0000 0000 0000 0000 0000 0000 0000 0001
---------------------------------------
1000 0000 0000 0000 0000 0000 0000 0000 ( See here MSB is switched on automatically for -ve )

Now convert to hexa : 80000000 ( every 4 bits together )

Simillarly with +ve numbers MSB is 0 ( switched off ).
Max +ve number is => (2^32)-1 ie
0111 1111 1111 1111 1111 1111 1111 1111 ( No calculation requires here as it is stored as it is )
So hex of this is : 7FFFFFFF

PLEASE LET ME KNOW IF YOU NEED SHORTCUT TO THIS PROCEDURE TO CALCULATE FASTER.

Wish you GOOD LUCK for your SCJP...
[ December 07, 2005: Message edited by: Enge Chall ]

Not everything that counts can be counted, and not everything that can be counted counts.
Bert Bates
author
Sheriff

Joined: Oct 14, 2002
Posts: 8898

5
Hi Guys -

Just to clarify, this topic is on the 1.4 exam, but it's NOT on the Tiger exam...

carry on

Spot false dilemmas now, ask me how!
(If you're not on the edge, you're taking up too much room.)
Enge Chall
Ranch Hand

Joined: Nov 22, 2005
Posts: 30
The algorithm looks tiger because of 32 bits. The same could be imagined for 4 bits for simplicity. cheers

In case someone gets any other -ve number, they can immediately pick the answer.
Greenhorn

Joined: Dec 06, 2005
Posts: 1
I need that 4 bits procedure for simplicity
I have not understood this.

Enge Chall
Ranch Hand

Joined: Nov 22, 2005
Posts: 30
What exactly you need in the 4 bit ?

Just take off all the 1's and 0's keeping the MSB and right side 3 bits as it is. That cut-shorts the procedure.