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Last modified: July 14, 2018

Simply put, *NaN* is a numeric data type value which stands for “not a number”.

In this quick tutorial, we’ll explain the *NaN *value in Java and the various operations that can produce or involve this value.

** NaN usually indicates the result of invalid operations.** For example, attempting to divide zero by zero is one such operation.

**We also use NaN for unrepresentable values.** The square root of -1 is one such case, as we can describe the value (

The IEEE Standard for Floating-Point Arithmetic (IEEE 754) defines the *NaN* value. **In Java, the floating-point types float and double implement this standard.**

Java defines* NaN* constants of both *float* and *double* types as *Float*.NaN and *Double.NaN*:

“*A constant holding a Not-a-Number (NaN) value of type double. It is equivalent to the value returned by Double.longBitsToDouble(0x7ff8000000000000L).”*

and:

*“A constant holding a Not-a-Number (NaN) value of type float. It is equivalent to the value returned by Float.intBitsToFloat(0x7fc00000).”*

We don’t have this type of constants for other numeric data types in Java.

While writing methods in Java, we should check that the input is valid and within the expected range. *NaN* value is not a valid input in most cases. Therefore, we should verify that the input value is not a *NaN* value and handle these input values appropriately.

*NaN* cannot be compared with any floating type value. This means that we’ll get *false* for all comparison operations involving *NaN* (except “!=” for which we get *true*).

We get *true* for “*x != x”* if and only if *x* is *NaN:*

System.out.println("NaN == 1 = " + (NAN == 1)); System.out.println("NaN > 1 = " + (NAN > 1)); System.out.println("NaN < 1 = " + (NAN < 1)); System.out.println("NaN != 1 = " + (NAN != 1)); System.out.println("NaN == NaN = " + (NAN == NAN)); System.out.println("NaN > NaN = " + (NAN > NAN)); System.out.println("NaN < NaN = " + (NAN < NAN)); System.out.println("NaN != NaN = " + (NAN != NAN));

Let’s have a look at the result of running the code above:

NaN == 1 = false NaN > 1 = false NaN < 1 = false NaN != 1 = true NaN == NaN = false NaN > NaN = false NaN < NaN = false NaN != NaN = true

Hence, **we cannot check for NaN by comparing with NaN using “==” or “!= “.** In fact, we should rarely use “==” or “!= ” operators with

Instead, we can use the expression “*x !*= x”*. *This expression returns true only for *NAN.*

We can also use the methods *Float.isNaN* and *Double.isNaN *to check for these values*. *This is the preferred approach as it’s more readable and understandable:

double x = 1; System.out.println(x + " is NaN = " + (x != x)); System.out.println(x + " is NaN = " + (Double.isNaN(x))); x = Double.NaN; System.out.println(x + " is NaN = " + (x != x)); System.out.println(x + " is NaN = " + (Double.isNaN(x)));

We’ll get the following result when running this code:

1.0 is NaN = false 1.0 is NaN = false NaN is NaN = true NaN is NaN = true

While doing operations involving *float* and *double* types, we need to be aware of the *NaN* values.

**Some floating-point methods and operations produce NaN values instead of throwing an Exception. **We may need to handle such results explicitly.

A common case resulting in not-a-number values are **mathematically undefined numerical operations**:

double ZERO = 0; System.out.println("ZERO / ZERO = " + (ZERO / ZERO)); System.out.println("INFINITY - INFINITY = " + (Double.POSITIVE_INFINITY - Double.POSITIVE_INFINITY)); System.out.println("INFINITY * ZERO = " + (Double.POSITIVE_INFINITY * ZERO));

These examples result in the following output:

ZERO / ZERO = NaN INFINITY - INFINITY = NaN INFINITY * ZERO = NaN

**Numerical operations which don’t have results in real numbers also produce NaN:**

System.out.println("SQUARE ROOT OF -1 = " + Math.sqrt(-1)); System.out.println("LOG OF -1 = " + Math.log(-1));

These statements will result in:

SQUARE ROOT OF -1 = NaN LOG OF -1 = NaN

All numeric operations with *NaN* as an operand produce *NaN* as a result:

System.out.println("2 + NaN = " + (2 + Double.NaN)); System.out.println("2 - NaN = " + (2 - Double.NaN)); System.out.println("2 * NaN = " + (2 * Double.NaN)); System.out.println("2 / NaN = " + (2 / Double.NaN));

And the result of the above is:

2 + NaN = NaN 2 - NaN = NaN 2 * NaN = NaN 2 / NaN = NaN

Finally, we cannot assign *null* to *double* or *float* type variables. Instead, we may explicitly assign *NaN* to such variables to indicate missing or unknown values:

double maxValue = Double.NaN;

In this article, we discussed *NaN* and the various operations involving it. We also discussed the need to handle *NaN* while doing floating-point computations in Java explicitly.

The full source code can be found over on GitHub.