public static native double atan (double a)

Returns the arc tangent of a value; the returned angle is in the range -pi/2 through pi/2. Special cases:

• If the argument is NaN, then the result is NaN.
• If the argument is zero, then the result is a zero with the same sign as the argument.

Parameters:

a

the value whose arc tangent is to be returned.

Returns:  the arc tangent of the argument.