Help Needed. New to Java Compound Interest Program....

[SubjectJ80]

Hi,

I'm new to Java programming and cannot seem to use printf correctly. I have a compound interest program, I have it nearly completed but cannot print in columns...

Can anyone help.....my output should be like this

Amount on deposit
Year 5% 6% 7% 8% 9% 10%
1 1050.00 1060.00 1070.00 1080.00 1090.00 1100.00
2 1102.50 1123.60 1144.90 1166.40 1188.10 1210.00
3 1157.63 1191.02 1225.04 1259.71 1295.03 1331.00
4 1215.51 1262.48 1310.80 1360.49 1411.58 1464.10
5 1276.28 1338.23 1402.55 1469.33 1538.62 1610.51
6 1340.10 1418.52 1500.73 1586.87 1677.10 1771.56
7 1407.10 1503.63 1605.78 1713.82 1828.04 1948.72
8 1477.46 1593.85 1718.19 1850.93 1992.56 2143.59
9 1551.33 1689.48 1838.46 1999.00 2171.89 2357.95
10 1628.89 1790.85 1967.15 2158.92 2367.36 2593.74

But I'm getting this:

Amount on Deposit
Year 5% 6% 7% 8% 9% 10%
1 1,050.00
2 1,102.50
3 1,157.63
4 1,215.51
5 1,276.28
6 1,340.10
7 1,407.10
8 1,477.46
9 1,551.33
10 1,628.89

Code:

public class InterestRates {


    public static void main(String[] args) 
    
    {
        double amount,amount1, amount2, amount3, 
                amount4, amount5;// amount on each deposit at the end of the year
        double principal = 1000.0; // amount before interest
        double rate = 0.05, rate1 = 0.06, rate2 = 0.07,rate3 = 0.08,
                rate4 = 0.09, rate5 = 0.10; // all interest rates
        
        // display headers
        System.out.println("Amount on Deposit");
        System.out.printf("%4s\t%10s\t%10s\t%10s\t%10s\t%10s\t%10s\t\n", 
                "Year", "5%", "6%", "7%", "8%", "9%", "10%");
        
        // calculate the amount on deposit for 5% rate for 10 years
        for( int year = 1; year <= 10; year++ )
        {
            // calculate the new amount for specified year
            amount = principal * Math.pow( 1.0 + rate, year );
            amount1 = principal * Math.pow( 1.0 + rate1, year );
            amount2 = principal * Math.pow( 1.0 + rate2, year );
            amount3 = principal * Math.pow( 1.0 + rate3, year );
            amount4 = principal * Math.pow( 1.0 + rate4, year );
            amount5 = principal * Math.pow( 1.0 + rate5, year );
            
            // display the year and the amount for the 5% rate
            System.out.printf("%4d%,20.2f\t\n", year, amount, amount1, 
                    amount2,amount3, amount4, amount5);
            
        }
            
    }
}

Can anyone show me what I am doing wrong??? Or just give me some advice, my code might be a bit crappy!!

Many Thanks.....

[pbrockway2]

When posting code use the "code" tags: put [code] at the start of the code and [/code] at the end. That way the formatting will be preserved when the code is displayed on a web page. The same goes for the tables.

System.out.printf("%4d%,20.2f\t\n", year, amount, amount1, 
        amount2,amount3, amount4, amount5);

This is only displaying the year and one of the amounts. SeeFormat string syntax in the API docs. And Formatting in Oracle's Tutorial.

[SubjectJ80]

Thank you for the info. I have added the code tags now. So I need to format it as a string and not use printf??

[pbrockway2]

No, you use printf(), but you need to replace "%4d%,20.2f\t\n" with a format string that will display all of the amounts.

[SubjectJ80]

Really sorry about this, but I don't know how to do that. I've looked over the Format string syntax in the API docs. And Formatting in Oracle's Tutorial and I'm none this wiser?

[pbrockway2]

Fair enough. They can be cryptic, but it's worth learning the bits you need as you come across the need because these format string (and similar) exist across lots of languages (C, Java, PHP etc).

%4d
% marks this as being a format instuction. Each %... corresponds to one of the arguments that follows the string.
d is for a decimal (base 10) integer
4 means four characters wide.

You can also use a zero and a minus sign to adjust formatting. This is most easily seen with an example. (The | symbol is just there so you can see the padding)

public class FormEg1 {
    public static void main(String[] args) {
        int year = 2011;
		
            // multiple % for multiple arguments
        System.out.printf("%6d %6d %6d\n", year, year + 1, year + 2);
            // - for left aligned, 0 for pad with zeros
        System.out.printf("|%6d|\n", year);
        System.out.printf("|%-6d|\n", year);
        System.out.printf("|%06d|\n", year);
    }
}

%20.2f
f is for floating point numbers
20 means 20 characters wide
.2 means rounded to 2 decimal places

Again there are variants including , which makes comma the thousands separator. Note also that %n can be used for newline.

public class FormEg2 {
    public static void main(String[] args) {
        double value = Math.PI * 1000;
            // padding and alignment as before
        System.out.printf("|%9.2f|%n", value);
        System.out.printf("|%09.2f|%n", value);
        System.out.printf("|%-9.2f|%n", value);
            // thousands
        System.out.printf("|%,9.2f|%n", value);
            // again, multiple % for multiple values...
        System.out.printf(
                "%12.2f%12.2f%12.2f%12.2f", 
                value, value * 10, value * 100, value * 1000);
    }
}

[SubjectJ80]

Scratch that. I finally got. Thank you so much for all your help. Your good deed is done!!

[pbrockway2]

You're welcome.