Adding Bill / Tax And Tip

I'm trying to make a simple program that will show the amount of a bill, the tip, tax and total with all 3 added.

Right now i am having issues with line 12. I am getting the error "Variable amount might not have been initialized

I thought i did initialized it.

import javax.swing.JOptionPane;
public class BillAmt {
public static void main(String[] arg) {
String amt;
double tax, taxTotal, tip, total;
tax = 6.75;
double amount;
taxTotal = amount + tax;
tip = taxTotal *.15;
total = tip + taxTotal;
amt = JOptionPane.showInputDialog("Please enter the amount: ");
amount = Double.parseDouble(amt);