.acos()

The Math.acos() method returns the inverse cosine (or arccosine) of the argument in radians.

Math.acos(n)

n is a double between 0 and 1.

The following example uses Math.acos() to return the inverse cosine of 0.0 and 1.0:

class Main {
  public static void main(String[] args) {
    double arg1 = 0.0;
    double arg2 = 1.0;

    System.out.println(Math.acos(arg1));
    System.out.println(Math.acos(arg2));
  }
}

This will produce the following output:

1.5707963267948966
0.0