Java has a built-in `Math` class, defined in the `java.lang` package, which contains important functions to perform basic mathematical operations. 

The class has the **`atan()` method**, which is used to compute an $\arctan$ or $\tan^{-1}$ (pronounced as "inverse tangent") of the specified value.

> If $tan(\theta)$ is x then $tan^{-1}$(x) or $arctan(x)$ is $\theta$.

# Method definition
```java
public  static double atan(double value);
```
## Parameter
**`value`** represents the double value for which we have to find the arc tangent.

## Return value
The function returns the double value corresponding to the arctangent of the `value`. The returned value will lie within the range $\pi/2$ to $-\pi/2$. 

> Note: `Math.PI` is a constant equivalent to $\pi$ in Mathematics.

If the `value` is infinity or #key# NaN :not a number #key#, then the returned value is NaN.

> Note: To convert an angle measured in radians to an equivalent angle measured in degrees and vice versa, you can use the built-in `Math.toDegrees(double angle_in_randians)` and `Math.toRadians(double angle_in_degrees)` methods.

# Code

class HelloWorld {
    public static void main( String args[] ) {
        double result = Math.atan(1);
        System.out.println("atan(1) = " + result);

        result = Math.atan(0);
        System.out.println("atan(0) = " +  result);

        result = Math.atan(0.48);
        System.out.println("atan(0.48) = " + result);

        result = Math.atan(0.66);
        System.out.println("atan(O.66) = " + result);

        result = Math.atan(0.8);
        System.out.println("atan(0.8) = " + result);

        result = Math.atan(1);
        System.out.println("atan(1) = " + result);

        result = Math.atan(Double.NaN);
        System.out.println("atan(NaN) = " + result);

        result = Math.atan(Double.POSITIVE_INFINITY);
        System.out.println("atan(∞) = " + result);
    }
}

What is Math.atan() in Java?

Java's Math.atan() computes the arctangent of a value, returning a double within the range of π/2 to -π/2.