java - 贷款利率返回错误值？

Question

好吧，我有这门课:

package com.sandrovictoriaarena.unittesting;

public class LoanCalculator {
private double pricipelValue; //PV
private double interestRate; //rate
private int loanLength; //n
private double result;

public LoanCalculator(double pricipelValue, double interestRate,
        int loanLength) {
    super();
    this.pricipelValue = pricipelValue;
    this.interestRate = interestRate / 100;
    this.loanLength = loanLength;
}

public double getPricipelValue() {
    return pricipelValue;
}

public void setPricipelValue(double pricipelValue) {
    this.pricipelValue = pricipelValue;
}

public double getInterestRate() {
    return interestRate;
}

public void setInterestRate(double interestRate) {
    this.interestRate = interestRate;
}

public int getLoanLength() {
    return loanLength;
}

public void setLoanLength(int loanLength) {
    this.loanLength = loanLength;
}

@Override
public String toString() {
    return "LoanCalculator [pricipelValue=" + 
    pricipelValue + ", interestRate=" + interestRate + 
    ", loanLength=" + loanLength + "]";
}

public double calculateMonthlyPayment() throws IllegalArgumentException{
    result = (1 - (Math.pow((1 + interestRate), -1 * loanLength)));
    result = interestRate / result;
    result = result * pricipelValue;
    return result;
}

}

我正在制作一个具有以下值的对象:新贷款计算器(100.0,20.0,6)；

我运行calculateMonthlyPayment()时的结果应该是17.65，但我一直得到30.07。我做错了什么？

Answer 1

代码和公式都是正确的。

您将利率设定为 20%，但年利率可能为 20%。我认为你的间隔是6，大概是六个月。您应该始终以与间隔数相同的方式传递利率。在这里，您的间隔数以月为单位，但您的利率以年为单位(每年)。因此，只需将利率传递为月利率，您就应该得到正确的答案!

月利率为20%/12 = (0.2/12)。如果您将其替换为输入，您将得到正确的答案。所以你应该这样做:new LoanCalculator (100.0,20.0/12,6)