Why does this print out -1.0?

Question

double num = Integer.MIN_VALUE + Integer.MAX_VALUE;
System.out.println(num);

Answer 1

Because there is one more negative number than positive.
And you explicitly wanted a double.

Answer 2

@1of3 is correct.
Try:
public class Program
{
public static void main(String[] args) {
//Integer.MIN_VALUE
double nummax = Integer.MAX_VALUE;
double nummin = Integer.MIN_VALUE;
//double numt =Integer.MIN_VALUE +Integer.MAX_VALUE;
double num = nummin + nummax;
System.out.println(nummax);
System.out.println(nummin);
//System.out.println(numt);
System.out.println(num);
}
}

Google floating pt vs integer.
Basically put: the computer is reading a certain number of 0’s and 1’s differently. Integers are direct. And from what I can see it is treating the integer memory as signed. Hence -num is the binary opposite of positive number.
e.g. if there is a 4 bit integer max would look like:
0111 = 7
Min would be:
1000 = -7 and not 8 or 1111 = 15 or -7 as you might expect
Floating point has to interpret it with perceived precision, since there is only a certain amount of numbers we can store with fix amount of memory.
Hence the discrepancy that you see.