Did I do this right? (Interest calculator)

[Rose Deanne]

There aren't any errors coming up, and the math part runs fine, I just want to make sure that this does what it's supposed to. I feel like I'm missing something.

What do you think? These were the instructions:
1. Ask the user for initial principal amount and annual percentage rate.
2. Program will go through the for-loop but instead of displaying in the screen, write to a text file.
3. Program will then open the same text file, read the data and append to the outputTextArea variable and then JOption display on the screen inside a JOptionPane message dialog.

import java.util.Scanner;
import java.io.*;
import java.text.NumberFormat;     //class for numeric formatting
import java.util.Locale;	       //class for country-specific information
import javax.swing.JOptionPane;
import javax.swing.JTextArea;

public class Interest3
{
	public static void main(String[] args) throws IOException
	{
		double amount,		//amount of deposit at end of each year
			   principal,	//initial amount before interest
			   rate;		//rate of interest
		String input;

		//create NumberFormat for currency in US dollar format
		NumberFormat moneyFormat = NumberFormat.getCurrencyInstance( Locale.US );

    	//create keyboard
    	Scanner keyboard = new Scanner(System.in);

    	//create JTextArea to display output
    	JTextArea outputTextArea = new JTextArea();

    	input = JOptionPane.showInputDialog("Please enter Principal: ");
    	principal = Double.parseDouble(input);

    	input = JOptionPane.showInputDialog("Please enter Interest Rate (Format: 0.00) ");
    	rate = Double.parseDouble(input);

    	//set first line to display output
    	outputTextArea.setText("Year\tAmount on deposit\n");

		//open new file
    	FileWriter fwriter = new FileWriter("MyMoneys.txt", true);
    	PrintWriter outputFile = new PrintWriter(fwriter);

    	//calculate amount on deposit for each of ten years
    	for (int year = 1; year<= 10; year++)
    	{
    		amount = principal * Math.pow(1.0 + rate, year);

			// append one line of text to outputTextArea
			outputTextArea.append( year + "\t" +
			moneyFormat.format(amount) + "\n");
    	}// end for

    	//close file
    	outputFile.close();
    	System.out.println("Data written to file");

    	//display results
    	JOptionPane.showMessageDialog(null, outputTextArea,
			"Compound Interest", JOptionPane.INFORMATION_MESSAGE);

    	System.exit(0);  //terminate the application

    }//end of main

}//end of Interest3.java

[Paul Clapham]

Step 3 starts out by saying

Program will then open the same text file, read the data and append to the outputTextArea variable...

It looks like you skipped that step and just used the data you already had in memory. Which would be a sensible thing to do in a real-life application, but not in a homework assignment which tells you to do something else.

[Rose Deanne]

Paul Clapham wrote:It looks like you skipped that step and just used the data you already had in memory.

Darn. Yeah, that's what I thought it was doing... I just really don't know what I'm missing in there. It's an online class where I'm basically just teaching myself out of a textbook, and the teacher rarely logs in to read his email, so I'm kinda stuck. What do I need to do?

[Darryl Burke]

Rose, please BeForthrightWhenCrossPostingToOtherSites.
http://www.java-forums.org/new-java/48463-did-i-do-right-interest-calculator.html

[Rose Deanne]

Darryl Burke wrote:Rose, please BeForthrightWhenCrossPostingToOtherSites.
http://www.java-forums.org/new-java/48463-did-i-do-right-interest-calculator.html

Oh, sorry, didn't realize that was an issue. Yeah, this is also posted to java-forums.org. It's just with the time zone difference and my wacky work schedule I don't really get to interact with people like I would like to, so I posted it to that place to maybe get a little bit more feedback.

[Rose Deanne]

Actually, I'm just gonna "resolve" this one so I don't make anyone angry. Thank you, Paul and Darryl.