Numbers - Java - page 176

can never be true. Instead, the methods Float.isNaN(float) and Double.isNaN(double)
must be used:

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

double double d = 123 ;

double double e = 0 ;

iif ( d / e == Double . POSITIVE_INFINITY )
System . out . println ( "Check for POSITIVE_INFINITY works" );
double

double s = Math . sqrt (- 1 );
iif ( s == Double . NaN )
System . out . println ( "Comparison with NaN incorrectly returns true" );
iif ( Double . isNaN ( s ))
System . out . println ( "Double.isNaN() correctly returns true" );

}

Note that this, by itself, is not sufficient to ensure that floating-point calculations have been
done with adequate accuracy. For example, the following program demonstrates a contrived
calculation—Heron's formula for the area of a triangle—both in float and in double . The
double values are correct, but the floating-point value comes out as zero due to rounding er-
rors. This happens because, in Java, operations involving only float values are performed as
32-bit calculations. Related languages such as C automatically promote these to double dur-
ing the computation, which can eliminate some loss of accuracy. Let's take a look:

public public class class Heron Heron {

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

// Sides for triangle in float
float

static void

float af , bf , cf ;
float float sf , areaf ;

// Ditto in double
double

double ad , bd , cd ;
double double sd , aread ;

// Area of triangle in float
af = 12345679.0f ;
bf = 12345678.0f ;
cf = 1.01233995f ;

sf = ( af + bf + cf )/ 2.0f ;
areaf = ( float float ) Math . sqrt ( sf * ( sf - af ) * ( sf - bf ) * ( sf - cf ));

System . out . println ( "Single precision: " + areaf );