casting question

[Kristof Camelbeke]

Hello...
On page 179 (Kathy&Bert) there is an example of casting a long into a byte:

long l = 130L;
byte b = (byte) l;
System.out.println ("the byte is " + b);

The result is : the byte is -126
If you look at the bit representation of 130
10000010 = 130
I don't understand after casting the number changes to -126 ???
[ December 29, 2003: Message edited by: Kristof Camelbeke ]

[B. Du Bois]

A long has 64 bits, a byte 8. When casting a long to a byte you will lose the first 56 bits:
130 as a long = 00000000...000010000010 (64 bits)
cast to a byte = 10000010 (8 bits)
Since the binary representation (two's complement) starts with a 1, this means that the number is negative. To get the decimal value, subtract 1 of the binary representation, invert the bits and put it in decimal representation:
10000010 - 1 = 10000001
after inversion = 01111110
decimal = -126

[Kristof Camelbeke]

Ok thanks for the explanation... Hope they don't ask many of these on the exam though (time-consuming)

[Vicken Karaoghlanian]

Originally posted by Kristof Camelbeke:
Ok thanks for the explanation... Hope they don't ask many of these on the exam though (time-consuming)

I wouldn't say time-consuming, check out my post here , i suggested an easy way to solve the problem.
Hope this helps.