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The isNaN() method of Java Double class is a built in method in Java returns true if this Double value or the specified double value is Not-a-Number (NaN), or false otherwise. Syntax:

public boolean isNaN()
        or
public static boolean isNaN(double val)

Parameters: The function accepts a single parameter val which specifies the value to be checked when called directly with the Double class as static method. The parameter is not required when the method is used as instance method. Return Value: It returns true if the val is NaN else it return false. Below programs illustrate isNaN() method in Java: Program 1:

Java

// Java code to demonstrate
// Double isNaN() method
// without parameter

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

        // first example
        Double f1 = new Double(1.0 / 0.0);

        boolean res = f1.isNaN();

        // printing the output
        if (res)
            System.out.println(f1 + " is NaN");
        else
            System.out.println(f1 + " is not NaN");

        // second example
        f1 = new Double(0.0 / 0.0);

        res = f1.isNaN();

        // printing the output
        if (res)
            System.out.println(f1 + " is NaN");
        else
            System.out.println(f1 + " is not NaN");
    }
}

Output:

Infinity is not NaN
NaN is NaN

Program 2:

Java

// Java code to demonstrate
// Double isNaN() method
// with parameter

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

        // first example
        Double f1 = new Double(1.0 / 0.0);

        boolean res = f1.isNaN(f1);

        // printing the output
        if (res)
            System.out.println(f1 + " is NaN");
        else
            System.out.println(f1 + " is not NaN");

        // second example
        f1 = new Double(0.0 / 0.0);

        res = f1.isNaN(f1);

        // printing the output
        if (res)
            System.out.println(f1 + " is NaN");
        else
            System.out.println(f1 + " is not NaN");
    }
}

Output:

Infinity is not NaN
NaN is NaN

Reference: https://docs.oracle.com/javase/7/docs/api/java/lang/Float.html#isNaN()

Double isNaN() method in Java with examples

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