I have a double in Java and I want to check if it is NaN
.
What is the best way to do this?
问题:
回答1:
Use the static Double.isNaN(double)
method, or your Double
's .isNaN()
method.
// 1. static method
if (Double.isNaN(doubleValue)) {
...
}
// 2. object's method
if (doubleObject.isNaN()) {
...
}
Simply doing:
if (var == Double.NaN) {
...
}
is not sufficient due to how the IEEE standard for NaN and floating point numbers is defined.
回答2:
Try Double.isNaN()
:
Returns true if this Double value is a Not-a-Number (NaN), false otherwise.
Note that [double.isNaN()
] will not work, because unboxed doubles do not have methods associated with them.
回答3:
You might want to consider also checking if a value is finite via Double.isFinite(value)
. Since Java 8 there is a new method in Double
class where you can check at once if a value is not NaN and infinity.
/**
* Returns {@code true} if the argument is a finite floating-point
* value; returns {@code false} otherwise (for NaN and infinity
* arguments).
*
* @param d the {@code double} value to be tested
* @return {@code true} if the argument is a finite
* floating-point value, {@code false} otherwise.
* @since 1.8
*/
public static boolean isFinite(double d)
回答4:
You can check for NaN by using var != var
. NaN
does not equal NaN
.
EDIT: This is probably by far the worst method. It's confusing, terrible for readability, and overall bad practice.
回答5:
Beginners needs practical examples. so try the following code.
public class Not_a_Number {
public static void main(String[] args) {
// TODO Auto-generated method stub
String message = "0.0/0.0 is NaN.\nsimilarly Math.sqrt(-1) is NaN.";
String dottedLine = "------------------------------------------------";
Double numerator = -2.0;
Double denominator = -2.0;
while (denominator <= 1) {
Double x = numerator/denominator;
Double y = new Double (x);
boolean z = y.isNaN();
System.out.println("y = " + y);
System.out.println("z = " + z);
if (z == true){
System.out.println(message);
}
else {
System.out.println("Hi, everyone");
}
numerator = numerator + 1;
denominator = denominator +1;
System.out.println(dottedLine);
} // end of while
} // end of main
} // end of class