Math class method abs()

[arun sabharwal]

Math.abs(INT_MIN_VALUE) gives a negative answer WHY? ANY EXPLAINATION.
ARUN

[shadow liu]

In \jdk1.3\src\java\lang\Math.java
it says:
/*********start***********/
/**
....
* Note that if the argument is equal to the value of
* <code>Integer.MIN_VALUE</code>, the most negative representable
* <code>int</code> value, the result is that same value, which is
* negative.
*
* @param a an <code>int</code> value.
* @return the absolute value of the argument.
* @see java.lang.Integer#MIN_VALUE
*/
public static int abs(int a) {
return (a < 0) ? -a : a;
}
/**************end***************/
IMHO, since the integer range is -2**31 to 2**31-1,
which means -2**31 is the only number that do not have
a opposite INTEGER value, so JDK leave it unchanged.
Just my guess.

[James Baud]

Math.abs(Integer.MIN_VALUE) returns Integer.MIN_VALUE

Java uses two's complement to represent integral values. To get the abs value of -41 we need to convert a negative value (-41) to a positive value (41). Here is how its done using two's complement. Note that I'm using a byte width for the purpose of discussion.

                                   Decimal Value           Binary
                                                             representation
Given                                  -41                  11010111
1's complement                                          00101000
Add 1                                                        00000001
Result (2's complement)         41                 00101001

We see here that the abs(-41) value is 41.
Now back to your original concern using Integer.MIN_VALUE:

                                     Decimal Value                 Binary
                                                                    representation
Given                            -2147483648        1000 0000 0000 0000
1's complement               2147483647        0111 1111 1111 1111
Add 1                                                       0000 0000 0000 0001
Result (2's complement) -2147483648         1000 0000 0000 0000

Hope this helps

------------------
~James Baud
He who asks, is a fool for five minutes;
but, he who does not ask, remains a fool forever. (Chinese proverb)