输出格式对齐问题

下面我写的这个代码在输出的时候数字由于小数的浮动很难对齐希望给予帮助..import javax.swing.JOptionPane;
public class Two { public static void main(String arg[]){
//prompt the user to enter the information
String loanString = JOptionPane.showInputDialog(null,
"Please enter loan amount \nFor example 10000.2:","Input",JOptionPane.QUESTION_MESSAGE);//get the loan amount

int loan = Integer.parseInt(loanString);// change the loan form string to int

String yearString = JOptionPane.showInputDialog(null,
"Please enter the number of years as an integer \nFor example 2:","Input",JOptionPane.QUESTION_MESSAGE);//get the year

int year = Integer.parseInt(yearString);// change the year form string to int

String rateString = JOptionPane.showInputDialog(null,
"Please enter the yearly rate \nFor example 3.4","Input",JOptionPane.QUESTION_MESSAGE);//get the yearly rate

double rate = Double.parseDouble(rateString);// change the rate form string to double

//calcuate monthlyrate,monthlypayment
double monthlyrate = (rate/1200);

double monthlypayment = (loan*monthlyrate / (1-(1/Math.pow((1+monthlyrate), year*12))));

double totalpayment = monthlypayment*year*12;

//declare variables
double principal = monthlypayment;
double interest =0;
double balance = loan;

//format to keep two digits after the decimal point
monthlypayment = (int)(monthlypayment*100) / 100.0;
totalpayment = Math.round(totalpayment*100) / 100.0;

String outputnumber= "";

String output="Loan Amount: "+loan+"\nNumber of Year: "+year+"\nAnnual interest rate: "
+(int)rate+"%"+"\nMonthly Payment: "+monthlypayment+"\nTotal Payment: "+totalpayment
+"\nPayment#"+"     "+"interest"+"     "+"Principal"+"     "+"Balance";

/*calculate the interest,principal and balance
and put them into output*/
for (int i=1; i<=year;i++){
for(int j=1;j<=12;j++){

interest = balance * monthlyrate;
interest = (int)(interest*100) / 100.0;
principal = monthlypayment - interest;
balance = balance - principal;
principal = (int)(principal*100) / 100.0;
balance = (int)(balance*100) / 100.0;
outputnumber = "                  "+interest+"          "+principal+"        "+balance;

output+="\n"+i+"-"+j +outputnumber;

}
}

JOptionPane.showMessageDialog(null,
output,"output",JOptionPane.INFORMATION_MESSAGE);

}

}