.atan()

The Math.atan() method returns the inverse tangent (or arctangent) of the argument in radians.

Math.atan(n)

n is a double whose arctangent is returned.

The following example uses Math.atan() to return the inverse tangent of 1.0:

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

    double x = 1.0;

    System.out.println(Math.atan(x));
    // Output: 0.7853981633974483
  }
}