Java，计算以下公式

Question

我正在尝试使用 Java 在图像中写入公式。但是，我得到了错误的输出。这就是我到目前为止的计算。

假设输入为：Loan Amount = 50000 and Length = 3 year。

我目前的输出是 'Monthly Payment' 的“676.08”和“总利息支付”的“25661.0”。

“每月付款”应为“1764.03”，“总利息付款”应为“13505.05”。

代码是：

//Program that displays the interest rate and monthly payment based on the loan amount and length of loan the user inputs.

import java.util.Scanner;

public class bankLoanSelection{

    public static void main(String[] args){
        
        Scanner input = new Scanner(System.in);

        //Declarations.

        double interestRate;
        final double n = 12;
        
        //Generates an account number in the range of 1 to 1000.

        int accountnumber = (int)(Math.random() * 1000)+1;

        //User input
        
        System.out.print("Enter Loan Amount: $");
        double L = input.nextDouble();
        System.out.print("Length of Loan (years): ");
        double i = input.nextDouble();

        //selection structure using if and if-else statements.

        if (L <= 1000)
        interestRate = .0825;
        else if (L <= 5000)
        interestRate = .0935;
        else if (L <= 10000)
        interestRate = .1045;
        else interestRate = .1625;
        
        
        //Computations. 

        double MonthlyPayment = L * (interestRate / n) * Math.pow(1 + interestRate / n, i * n) / Math.pow(1 + interestRate / n, i * n) - 1;
        double TotalAmountOfLoan = MonthlyPayment * i * n;
        double TotalInterest = L - TotalAmountOfLoan;

        //Output.

        System.out.println("Account Number: #" + accountnumber);
        System.out.println("Loan Amount: $" + L);
        System.out.println("Loan Length (years): " + i);
        System.out.println("Interest Rate: " + interestRate * 100 + "%");
        System.out.printf("Total Monthly Payment: $%.2f%n", MonthlyPayment); //Rounds second decimal
        System.out.println("Total Interest Payments: $" + TotalInterest);
        
    }

}

Answer 1

您需要更正分母中括号的排列，正确的公式为：

double numerator = L * (interestRate / n) * Math.pow(1 + interestRate / n, i * n)
double denominator = Math.pow(1 + interestRate / n, i * n) - 1;
double MonthlyPayment = numerator / denominator;

尝试将问题分解成更小的单元来解决。

Answer 2

你必须在条件之间加上圆括号。

应该是：

double MonthlyPayment = L * ((interestRate / n) * Math.pow(1 + interestRate / n, i * n)) 
                             / (Math.pow(1 + interestRate / n, i * n) - 1);

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