public class JoyOfHex {
public static void main(String[] args) {
System.out.println(
Long.toHexString(0x100000000L + 0xcafebabe));
}
}
I got the problem from Java Puzzlers Book
Here Is Their Explanation ::
------------------------------------------------
Decimal literals have a nice property that is not shared by
hexadecimal or octal literals: Decimal literals are all positive [JLS
3.10.1]. To write a negative decimal constant, you use the unary
negation operator (-) in combination with a decimal literal. In this
way, you can write any int or long value, whether positive or
negative, in decimal form, and negative decimal constants are clearly
identifiable by the presence of a minus sign. Not so for hexadecimal
and octal literals. They can take on both positive and negative
values. Hex and octal literals are negative if their high-order bit is
set. In this program, the number 0xcafebabe is an int constant with
its high-order bit set, so it is negative. It is equivalent to the
decimal value -889275714.
The addition performed by the program is a mixed-type computation: The
left operand is of type long, and the right operand is of type int. To
perform the computation, Java promotes the int value to a long with a
widening primitive conversion [JLS 5.1.2] and adds the two long
values. Because int is a signed integral type, the conversion performs
sign extension: It promotes the negative int value to a numerically
equal long value.
The right operand of the addition, 0xcafebabe, is promoted to the long
value 0xffffffffcafebabeL. This value is then added to the left
operand, which is 0x100000000L. When viewed as an int, the high-order
32 bits of the sign-extended right operand are -1, and the high-order
32 bits of the left operand are 1. Add these two values together and
you get 0, which explains the absence of the leading 1 digit in the
program's output. Here is how the addition looks when done in
longhand. (The digits at the top of the addition are carries.)
1111111
0xffffffffcafebabeL
+ 0x0000000100000000L
0x00000000cafebabeL
------------------------------------------------
What I Do Not Understand Is That How Exactly Does One Can See (Or
Guess) A Hex Word --cafebabe-- and deduce that it's most significant
bit is one ergo it is going to represented as -ve :
Apologies if I am missing something too naive
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