Ensuring the Accuracy of Floating-Point Numbers
Problem
You want to know if a floating-point computation generated a sensible result.
Solution
Compare with the
INFINITY
constants, and use isNaN( )
to check for
“not a number.”
Fixed-point operations that can do things like divide by zero will result in Java notifying you abruptly by throwing an exception. This is because integer division by zero is considered a logic error.
Floating-point operations, however, do not throw an exception,
because they are defined over an (almost) infinite range of values.
Instead, they signal errors by producing the constant
POSITIVE_INFINITY if you divide a positive floating-point number by
zero, the constant NEGATIVE_INFINITY if you divide a negative
floating-point value by zero, and NaN
, (Not a
Number) if you otherwise generate an invalid result. Values for these
three public constants are defined in both the
Float
and the Double
wrapper
classes. The value NaN
has the unusual property
that it is not equal to itself, that is, NaN
!=
NaN
. Thus, it would hardly make sense to compare a
(possibly suspect) number against NaN
, because the
expression:
x == NaN
can therefore never be true. Instead, the methods
Float.isNaN(float)
and
Double.isNaN(double)
must be used:
// InfNan.java public static void main(String argv[]) { double d = 123; double e = 0; if (d/e == Double.POSITIVE_INFINITY) System.out.println("Check for POSITIVE_INFINITY works"); double s = Math.sqrt(-1); if (s == Double.NaN) System.out.println("Comparison ...
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