Numbers - Java - page 180

Solution

If you simply cast a floating value to an integer value, Java truncates the value. A value like
3.999999 cast to an int or long becomes 3, not 4. To round floating-point numbers properly,
use Math.round() . It has two overloads: 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, for some bizarre reason, you
wanted to round numbers greater than 0.54 instead of the normal 0.5, you could write your
own version of round() :

public public class Round {

/** We round a number up if its fraction exceeds this threshold. */
public

class Round

public static static final final double double THRESHOLD = 0.54 ;

/*
* Round floating values to integers.
* @return the closest int to the argument.
* @param d A non-negative values to be rounded.
*/
public public static static int int round ( double double d ) {

return return ( int int ) Math . floor ( d + 1.0 - THRESHOLD );

}

public public static static void void main ( String [] argv ) {

for for ( double double d = 0.1 ; d <= 1.0 ; d += 0.05 ) {

System . out . println ( "My way: " + d + "-> " + round ( d ));
System . out . println ( "Math way:" + d + "-> " + Math . round ( d ));

}

}

}

If, on the other hand, you simply want to display a number with less precision than it nor-
mally gets, you probably want to use a DecimalFormat object or a Formatter object, which
we look at in Formatting Numbers .