public static double pv(double rate, double numberOfPeriod, double payment) {
    double retval = 0;
    boolean t = false;
    if (rate == 0) {
        retval = -1*((numberOfPeriod*payment));
    }
    else {
        double r1 = rate + 1;
        retval =
                (( ( 1 - Math.pow(r1, numberOfPeriod) ) / rate ) * (t ? r1 : 1)  * payment - 0) 
                /
                Math.pow(r1, numberOfPeriod);
    }
    return retval;
}

式中，t是类型-付款到期时。0=期末，1=期初。默认值为0。