Problems getting floating point number to show in GUI...

Hello! So I'm trying to get the very last part of this code to show up as "The total accumulation is: $(whateverMynumberEquals)" in the GUI. The problem is that I'm using a floating point and I have no clue how to put it in proper form so that it shows up correctly. I put what I THOUGHT it would be below, so you can tell me what's right and what's not. Or should I make it a variable and THEN put it in the GUI? I just need the box to show the number with two decimal points only. Anyways, as you can see, I don't know what I'm doing with it, so please help! Thanks!

Code Java:

import java.util.Scanner;
import javax.swing.JOptionPane;
public class CompoundInterest {
 
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		Scanner QWERTY = new Scanner(System.in);
		JOptionPane.showMessageDialog(null, "Welcome to the Compound Interest Calculator!");
		JOptionPane.showMessageDialog(null, "We are going to ask you for certain information in order calculate your interest!");
		System.out.println();
 
		double P = 0;
		P = Double.parseDouble(
				JOptionPane.showInputDialog("What is the initial deposit (principle)? Numbers only please!"));
		JOptionPane.showMessageDialog(null, "The value entered is: $" + P);
 
		double r = 0;
		r = Double.parseDouble(
			JOptionPane.showInputDialog("What is the annual interest rate in percent? [xx.yy]"));
		JOptionPane.showMessageDialog(null, "The value entered is: " + r);
 
		int q = 0;
		q = Integer.parseInt(
			JOptionPane.showInputDialog("What is the number of times the compounding is done per year?"));
		JOptionPane.showMessageDialog(null, "The value entered is: " + q);
 
		double n = 0;
		n = Double.parseDouble(
			JOptionPane.showInputDialog("How many years is the principle left in deposit?"));
		JOptionPane.showMessageDialog(null, "The value entered is: " + n);
 
		r = (r/100);
		double exponent = Math.pow(1 + r/q, n*q);
 
		double A = 0;
		A = P * exponent;
		JOptionPane.showMessageDialog(null, "The total accumulation is:" + 
			System.out.printf("$%.2f\n", A));
 
 
	}
 
}