June 2001
Intermediate to advanced
888 pages
21h 1m
English
You need to round floating-point numbers to integer or to a particular precision.
If you simply
cast a floating value to an
integer value, Java will truncate the value. A value like 3.999999
casted to an int or long will
give 3, not 4. To round these properly, use Math.round( )
. There are two forms; if you give it a
double, you get a long result.
If you give it a float, you get an
int.
What if you don’t like the rounding rules used by
round? If you wanted to round numbers greater than
0.54 instead of the normal 0.5, you could write your own version of
round( ):
// Round.java
/** Round a number up if its fraction exceeds this threshold. */
public static final double THRESHOLD = 0.54;
/* Return the closest long to the argument.
* ERROR CHECKING OMITTED.
*/
static long round(double d) {
long di = (long)Math.floor(d); // integral value below (or ==) d
if ((d - di) > THRESHOLD)
return di + 1;
else return di;
}If you need to display a number with less precision than it normally
gets, you will probably want to use a
DecimalFormat object.