Java净现值

Question

我试图以固定的速度计算这么多年后的净现值，当我运行它时，我总是得到我想要的数字的负号，但当我去掉最后一行中的负号时，同样的问题也发生了。当我的代码读作

public static double netPresentValue(double investment, int years, double payout, double r) {
    double count = 0;
    for (int i = 1; i == years; i++) {
        investment =   presentValue(payout, i, r) - investment; 
    } 
    return -investment;
}

-90909是预期的，但在我写的时候会得到+90909

public static double netPresentValue(double investment, int years, double payout, double r) {
    double count = 0;
    for (int i = 1; i == years; i++) {
        investment =   presentValue(payout, i, r) - investment; 
    } 
    return investment;
}

对于第零年，我收到的代码应该是-100000，但我得到的是100000

Answer 1

我意识到第一年唯一发生的事情是债务被实例化，你应该从负投资开始，然后每年增加新的支出。

public static double netPresentValue(double investment, int years, double payout, double r) {
    double debt = 0.0;
    for (int i = 0; i <= years; i++) {
    if (i == 0) {
    debt = -investment; 
    }//
    else {
    debt = debt + presentValue(payout, i, r);
    }//end else
    }//end for loop 
    return debt;
    }