sine function btw

sine.java

public class sine {
    /*
    * This Class does sine function without any need to use Math.sin
    * @author Morad A.
    */
    static double PI = 3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679d;
    public static void main(String[] args) {
        System.out.printf("%.19f\n",sin(30d)); // print the result to 19 decimal places of sin(30 deg.)
    }
    /*
    * Does sine function
    * @param in the input in deg.
    * @return result of sine of input deg
    */
    public static double sin(double in) {
        double ret = 0d;
        in = toRadian(in);
        double initOddNum = 3d; // inital odd number
        boolean arthSwitch = false; // false: - , true : +
        ret = in;
        for(int i = 0;i<20;i++) {
            if(arthSwitch) { // true / +
                ret = ret + (power(in, initOddNum)/factorial(initOddNum));
            }else { // false / -
                ret = ret - (power(in,initOddNum)/factorial(initOddNum));
            }
            initOddNum = initOddNum + 2d; // to the next odd number
            arthSwitch = !arthSwitch; // flip the switch
        }
        return ret;
    }
    /*
    * Converts deg. to rad.
    * @param deg the input degree
    * @return the radian value equilivant to degree
    */
    public static double toRadian(double deg) {
        double ret = 0d;
        ret = deg * (PI/180d);
        return ret;
    }
    /*
    * Does factorial operation " eg. 4! "
    * @param a the number to be factored "we'll call it x"
    * @return the result of x!
    */
    public static double factorial(double a) {
        if(a == 0d) return 1d;
        return a*factorial(a-1d);
    }
    /*
    * Does the power function faster than Math.pow
    * @param x the base
    * @param y the exponential
    * @return the result
    */
    public static double power(double x, double y){
        double temp;
        if (y == 0) {
            return 1;
        }
        temp = power(x, y / 2);
        if (y % 2 == 0) {
            return temp * temp;
        }
        else {
            if (y > 0) {
                return x * temp * temp;
            }else{
                return (temp * temp) / x;
            }
        }
    }
}