Java for循环未返回预期值

Question

为了澄清所使用的输入是100，用于投资金额，利率为5%（在该程序中，取5/100，然后/12=0.00417），在这种情况下，投资的持续时间为6个月。因此，在任何利息累积之前的第0个月，没有利息，所以这只是投资的投入金额（100）。然后，在第一个月，它现在运行正常（（100*i）*（i interest（））；或在或情况下（（100*1）*（10.00417））=100.417

但当我到了第二个月，而不是期望的201.252，我得到了400.833。

我正在做一项作业，作业中的输出应显示为：

Months Account Value

------ --------------

0       100.000

1       100.417

2       201.252

3       302.507

4       404.184

5       506.285

6       608.811

但我的表现是：

Months   Account Value 

    0       100.000
    1       100.417
    2       400.833
    3       901.250
    4       1601.667
    5       2502.083
    6       3602.500

我可以看到，我的计算错误是在方法的某处，量保存（），

这是我的类代码：

import java.text.DecimalFormat;

/*
 * Click nbfs://nbhost/SystemFileSystem/Templates/Licenses/license-default.txt to change this license
 * Click nbfs://nbhost/SystemFileSystem/Templates/Classes/Class.java to edit this template
 */

/**
 *
 * @author stephaniebrandon
 */
public class AccountValue {

    private double amount;
    private double rate;
    private double months;
    
    private static final DecimalFormat df = new DecimalFormat("0.000");

    //Gets value of amount being inputted into account montly
    public double getAmount() {
        return amount;
    }

    //gets value of interest rate annually
    public double getRate() {
        return rate;
    }

    //gets value of amount of months investment will accumulate
    public double getMonths() {
        return months;
    }

    public void setAmount(double newAmount) {
        amount = newAmount;
    }

    public void setRate(double newRate) {
        rate = newRate;
    }

    public void setMonths(double time) {
        months = time;
    }

    //Serive Methods
    //Interest calculation
    public double interest() {
        double total = 0.0;
        total += ((getRate() / 100) / 12);
        return total;
    }

    //calculate accumulated interest in account
    /**
     * public double amountSaved(){ double total=0.0; total += (getAmount() *
     * getRate() * getMonths()); return total; }
     */
    public void amountSaved() {
        double total = 0.0;
        double val = 0.0;
        System.out.println("\n Months \t Account Value \n");
        for (int i = 0; i <= getMonths(); i++) {
            if(i==0){
                val+= getAmount();
            }else
            val = ((getAmount() * i) * (i + interest()));
            System.out.println("\t" + i + "\t\t" + df.format(val));     
        }
       
    }

    //String returns description of object desired by dev
    @Override
    public String toString() {
        String output = "";
        output += "Montly savings Amount: $" + amount + "\n Annual interest rate, in percent: "
                + getRate() + "% " + "\nNumber of Months: " + months + "\n"+ interest();
        return output;
    }

}

以及测试人员课程：

import java.util.Scanner;

/*
 * Click nbfs://nbhost/SystemFileSystem/Templates/Licenses/license-default.txt to change this license
 * Click nbfs://nbhost/SystemFileSystem/Templates/Classes/Main.java to edit this template
 */

/**
 *
 * @author stephaniebrandon
 */
public class AccountValueTester {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        
        //Scanner object
        Scanner scan = new Scanner(System.in);
        
        //Create an account value object
        
        AccountValue myAccount;
        
        myAccount = new AccountValue();
        
        //Get info from user
        System.out.println("Enter amount, interest rate and number of months");
        int inputA = scan.nextInt();
        myAccount.setAmount(inputA);
        int inputB = scan.nextInt();
        myAccount.setRate(inputB);
        int inputC = scan.nextInt();
        myAccount.setMonths(inputC);
        System.out.println(myAccount);
        myAccount.amountSaved();
    }
    
}

Answer 1

if(i==0){
            val+= getAmount();
        }else
        val += ((getAmount()) * (i + interest()));

在第0步，val=100.000；在第1步，val=100.000（100.000*（i利息））

这就是为什么你有不受欢迎的价值。

如果你需要的话

0 100.000

1 100.417

2 201.252

3 302.507

4 404.184

5 506.285

6 608.811

然后它应该在i=1（但应该运行并调试）

val = ((getAmount() * i) * (i + interest()));