How to implement JOptionPane.showConfirmDialog in my code

This is what I have gotten so far and it debugs with no errors. Now I need to implement the JOptionPane.showConfirmDialog function to prompt the user as to whether 'End program' or not.

<code>
  public static void main(String args[]) throws IOException {
    BufferedReader stdin  = new BufferedReader (new InputStreamReader(System.in));  //Declare stdin  Input
    String yearString, valueString; //Define variable yearString, valueString
    // Prompt the user to enter the degree in fahrenheit
    String fahrenheitString = JOptionPane.showInputDialog(null,
        "Enter a Fahrenheit degree to convert it to Celsius", "Input", JOptionPane.QUESTION_MESSAGE);
    // Convert String to Double
    double Fahrenheit = Double.parseDouble(fahrenheitString);
    // Convert from Fahrenheit to Celsius
    double Celsius = (5.0/9) * (Fahrenheit - 32);
    // Display output
    String output = + Fahrenheit + " degree fahrenheit is equal to " + Celsius + " degree celsius";
    JOptionPane.showMessageDialog(null, output, "Output", JOptionPane.INFORMATION_MESSAGE);

    System.exit(0);
</code>
Thanks