Reference on primitive types - Multimedia Introduction to Programming Using Java - page 220

Number”, and from then on your results are garbage. Division x/0D
where x is nonzero produces either Double.POSITIVE_INFINITY or
Double.NEGATIVE_INFINITY , and from then on your results are garbage.
Do not divide by 0, except for fun.
• % : Remainder . e.g 5.2 % 5 evaluates to 0.20000000000000018 . (You
would expect it to evaluate to 0.2 , but roundoff error is involved.)
The arithmetic relations < , <= , > , and >= can be used on values of type dou-
ble . For example, 1.3241 < 1.3241001 evaluates to tru e.
The operators == and != can also be used with double operands. However,
these operators are rarely used because double values are only approximations.
Rather than checking for equality, one usually checks whether two double val-
ues are “close enough” —i.e. whether their absolute difference is small enough.
Precedence and associativity of double operators
The double operators have the same precedence and associativity properties
as their int counterparts. See Sec. 6.1.
Discussion
Type double is not as simple and straightforward as the above introduction
might indicate. This is because double numbers are only finite approximations
to real numbers. For example, the value of Math.PI , the closest possible approx-
imation to the ratio of the circumference of a circle to its diameter, is
3.141592653589793
but actually the fractional part of this ratio is not finite but goes on forever. It
does not even repeat (e.g. the rational number 1/4 can be written as .25000... ;
the fraction consists of a non-repeating part 25 followed by a part, 0 , which
repeats forever).
Further, literals (like 3.141592653589793 ) are written in decimal, but they
are stored in the computer in binary, and the conversion from decimal to binary
is another source of error.
Finally, double operations cannot be exact. For example:
(1D / 48D) * 48D is printed as 1.0 , but
(1D / 49D) * 49D is printed as 0.9999999999999999 .
So these two expressions are not equal in double arithmetic. Run this loop below
and analyze its output to see some of the approximations that go on. Because
double values are only approximations, do not write a loop whose loop counter
is a double .