Need Some Java Help With a Loan Calculator

I'm trying to make a loan program that calculates the number of months it takes to pay off a loan while also printing out the Payment, Balance, Interest, and Principle. Heres what I have so far..

Code:

import javax.swing.*;
import java.awt.*;
import javax.swing.JOptionPane.*;
import java.text.DecimalFormat;
import java.text.NumberFormat;

public class MonthlyPayment {
	public static void main(String[] args) {
		// Declaration of variables
		double I; // Monthly interest rate
		double Balance = (double) -1; // Amount borrowed
		double InterestRate = (double) -1; // Annual interest rate
		double MonthlyPayment = (double) -1; // Monthly payment
		double Interest; // Amount owed through interest
		double TotalInterest=(double) 0; //
		double Principle=(double) 0; // Part that goes towards paying off the loan
        int Payment=0;
		NumberFormat form;
        DecimalFormat DF=new DecimalFormat("###00");
        form=NumberFormat.getCurrencyInstance();
		
       // Prompting the user for the loan, annual interest, and monthly payment
        while (Balance <= 0) { // Prompting positive value greater than zero
			String Prompt = "Enter the Loan Amount:";
			String Data = JOptionPane.showInputDialog(Prompt, "0");
			if (Data == null)
				return;
			Balance = Double.parseDouble(Data);
		}

		while (InterestRate <= 0) {
			String Prompt = "Enter the Annual Interest Rate:";
			String Data = JOptionPane.showInputDialog(Prompt, "0");
			if (Data == null)
				return;
			InterestRate = Double.parseDouble(Data);
		}
		while (MonthlyPayment < 0) {
			String Prompt = "Enter the Monthly Payment:";
			String Data = JOptionPane.showInputDialog(Prompt, "0");
			if (Data == null)
				return;
			MonthlyPayment = Double.parseDouble(Data);
		}
		//calculations
		I=InterestRate/12;
		System.out.println();
		while(Balance>MonthlyPayment){
			Interest=Balance*I;
			TotalInterest=TotalInterest+Interest;
			Principle=MonthlyPayment-Interest;
			System.out.println(Payment+""+DF.format(Balance)+""+DF.format(Interest)+""+DF.format(Principle));
		    Payment=Payment+1;
		    
		}
		
	}
	

}

its stuck in an infinite loop for some reason....

 

It is your last loop in your program. You never update your variable "Balance" so it will always stay greater than MonthlyPayment.

 

alright..i updated it by adding the following to the while loop:

Balance=Balance-Principle

but now it prints out really strange numbers...like when i type in 1000 for the loan amount, .09* for interest rate, and 90 for the monthly payment, the output is:


09180882
18340783
27510684
36660684
45810585
54960486
64090486
73220387
82350288
91470288
10580189

 

ahh ic..i added spaces in between and i now get the output:

0 918 08 82
1 834 07 83
2 751 06 84
3 666 06 84
4 581 05 85
5 496 04 86
6 409 04 86
7 322 03 87
8 235 02 88
9 147 02 88
10 58 01 89

but the balance, interest, Principle are in incorrect number formats..i want them to be decimal currency

 

Code:

	NumberFormat form;
        DecimalFormat DF=new DecimalFormat("###00");
        form=NumberFormat.getCurrencyInstance();

You created a NumberFormat object for currency (money) purposes that you don't use and you tried to create a DecimalFormat object that you do use but isn't doing what you want.

Just use the NumberFormat object you created instead of the DecimalObject one since it's specifically designed for money there's no point trying to create one yourself. After that, remove the unneeded DecimalFormat variable and you're done.

Spoiler alert:
0 $917.50 $7.50 $82.50
1 $834.38 $6.88 $83.12
2 $750.64 $6.26 $83.74
3 $666.27 $5.63 $84.37
4 $581.27 $5.00 $85.00
5 $495.63 $4.36 $85.64
6 $409.34 $3.72 $86.28
7 $322.41 $3.07 $86.93
8 $234.83 $2.42 $87.58
9 $146.59 $1.76 $88.24
10 $57.69 $1.10 $88.90

 

awesome..it worked! thank you so much