The IEEE 754 format has one bit reserved for the sign and the remaining bits representing the magnitude. This means that it is "symmetrical" around origo (as opposed to the Integer values, which have one more negative value). Thus the minimum value is simply the same as the maximum value, with the sign-bit flipped, so yes, -Double.MAX_VALUE is the lowest actual number you can represent with a double.
I suppose the Double.MAX_VALUE should be seen as maximum magnitude, in which case it actually makes sense to simply write -Double.MAX_VALUE. It also explains why Double.MIN_VALUE is the least positive value (since that represents the least possible magnitude).
But sure, I agree that the naming is a bit misleading. Being used to the meaning Integer.MIN_VALUE, I too was a bit surprised when I read that Double.MIN_VALUE was the smallest absolute value that could be represented. Perhaps they thought it was superfluous to have a constant representing the least possible value as it is simply a - away from MAX_VALUE :-)
(Note, there is also Double.NEGATIVE_INFINITY but I'm disregarding from this, as it is to be seen as a "special case" and does not in fact represent any actual number.)
Here is a good text on the subject.
Answer from aioobe on Stack OverflowThe IEEE 754 format has one bit reserved for the sign and the remaining bits representing the magnitude. This means that it is "symmetrical" around origo (as opposed to the Integer values, which have one more negative value). Thus the minimum value is simply the same as the maximum value, with the sign-bit flipped, so yes, -Double.MAX_VALUE is the lowest actual number you can represent with a double.
I suppose the Double.MAX_VALUE should be seen as maximum magnitude, in which case it actually makes sense to simply write -Double.MAX_VALUE. It also explains why Double.MIN_VALUE is the least positive value (since that represents the least possible magnitude).
But sure, I agree that the naming is a bit misleading. Being used to the meaning Integer.MIN_VALUE, I too was a bit surprised when I read that Double.MIN_VALUE was the smallest absolute value that could be represented. Perhaps they thought it was superfluous to have a constant representing the least possible value as it is simply a - away from MAX_VALUE :-)
(Note, there is also Double.NEGATIVE_INFINITY but I'm disregarding from this, as it is to be seen as a "special case" and does not in fact represent any actual number.)
Here is a good text on the subject.
These constants have nothing to do with sign. This makes more sense if you consider a double as a composite of three parts: Sign, Exponent and Mantissa. Double.MIN_VALUE is actually the smallest value Mantissa can assume when the Exponent is at minimun value before a flush to zero occurs. Likewise MAX_VALUE can be understood as the largest value Mantissa can assume when the Exponent is at maximum value before a flush to infinity occurs.
A more descriptive name for these two could be Largest Absolute (add non-zero for verbositiy) and Smallest Absolute value (add non-infinity for verbositiy).
Check out the IEEE 754 (1985) standard for details. There is a revised (2008) version, but that only introduces more formats which aren't even supported by java (strictly speaking java even lacks support for some mandatory features of IEEE 754 1985, like many other high level languages).
According to the javadoc for Double.MIN_VALUE, MIN_VALUE is:
A constant holding the smallest positive nonzero value of type double
So Double.MIN_VALUE is not negative, it's the positive value that's as close as a Double can get to zero (without being zero).
Double.MIN_VALUE is the smallest positive non-zero value which can be represented by a Java double (see the JavaDoc at http://download.oracle.com/javase/8/docs/api/java/lang/Double.html).
Okay, let's see what we get from Double.MIN_VALUE. When we say,
System.out.println(Double.MIN_VALUE);
It prints out that the minimum double value is 4.9E-324, which is POSITIVE and NONZERO.
In your code you compare it to 0. Even though how small 4.9E-324 is, it is still greater than 0.
If you are trying to find the smallest negative double that you can get, then you are looking for,
System.out.println(-Double.MIN_VALUE);
This will return -4.9E-324, which is the smallest and negative number that you can get with Double.
Because Double.MIN_VALUE is positive and nonzero. According to Oracle doc:
MIN_VALUE: A constant holding the smallest positive nonzero value of type double, 2-1074. It is equal to the hexadecimal floating-point literal 0x0.0000000000001P-1022 and also equal to Double.longBitsToDouble(0x1L).
Think about it in these terms. Take a 2-bit number with a preceding sign:
000 = 0
001 = 1
010 = 2
011 = 3
Now let's have some negatives:
111 = -1
110 = -2
101 = -3
Wait, we also have
100 ...
It has to be negative, because the sign-bit is 1. So, logically, it must be -4.
(Edit: As WorldEngineer rightly points out, not all numbering systems work this way -- but the ones you're asking about do.)
Because there are not two classes of numbers in the integer range, but three: negative numbers, zero, and positive numbers. Zero has to take up a slot (would be rather impractical not to be able to represent zero...), so either the positive or the negative class has to give up a slot. The fact that it's usually the positive range that has to make that sacrifice is to a certain extent arbitrary, but on the level of bit manipulations there are some things that this decision makes more convenient.