初学者需要实际的例子。所以试试下面的代码。

public class Not_a_Number {

public static void main(String[] args) {
    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

下面的代码片段将帮助计算持有基元类型的NaN。

double dbl = double . nan; Double.valueOf(双).isNaN () ?真:假;

你可能还想通过Double.isFinite(value)检查一个值是否为有限值。自Java 8以来，在Double类中有一个新方法，您可以立即检查值是否为NaN和无穷大。

/**
 * 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)

尝试Double.isNaN ():

如果此Double值为非数字(NaN)则返回true，否则返回false。

注意，[double.isNaN()]将不起作用，因为未装箱的双精度对象没有与它们关联的方法。

你可以使用var != var来检查NaN。NaN不等于NaN。

编辑:这可能是迄今为止最糟糕的方法。它令人困惑，可读性很差，而且总体来说是糟糕的做法。

初学者需要实际的例子。所以试试下面的代码。

public class Not_a_Number {

public static void main(String[] args) {
    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