Service Level generates tip %

mainClass

import javax.swing.*;
import javax.swing.text.StringContent;

public class mainClass {
    public static void main(String[] args) {

        double bill=0;
        double tip=0;
        int serviceLevel=0;
        int periodCounter = 0;

        String diningExperience = JOptionPane.showInputDialog(null, "Using numbers from 1 - 10 please rate your dining experience." +
                "1 being very unsatisfied, 10 being extremely satisfied.");


        if (diningExperience.contains(".")){
                JOptionPane.showMessageDialog(null, "You must enter an INTEGER value");
                System.exit(0);
            }

        try {
            serviceLevel = Integer.parseInt(diningExperience);
        }
        catch(NumberFormatException e){
            JOptionPane.showMessageDialog(null, "You must enter an INTEGER value, "+diningExperience+" is NOT an integer value");
            System.exit(0);
        }

        if (serviceLevel > 10 || serviceLevel < 1){
            JOptionPane.showMessageDialog(null, "You must enter an integer between 1 and 10");
            System.exit(0);
        }

        String diningCost = JOptionPane.showInputDialog(null, "How much was the bill?");

        for (int i = 0; i < diningCost.length(); i++) {
            char buffer = diningCost.charAt(i);
            if (buffer == '.') {
                periodCounter++;
            }
            if (periodCounter > 1) {
              JOptionPane.showMessageDialog(null, "Your bill must be a valid currency amount (this is not an IP address!)");
                System.exit(0);

            }


        }

        try {
            bill = Double.parseDouble(diningCost);
        }
        catch(NumberFormatException e){
            JOptionPane.showMessageDialog(null, "The bill you entered was NOT a number :(");
            System.exit(0);
        }
        String formattedCost = String.format("%.2f", bill);

        JOptionPane.showMessageDialog(null, "Your bill is " + formattedCost);

        tip = 0;
        if(serviceLevel < 5){
            tip = .10 * bill;
        }
        if(serviceLevel >= 5){
            tip = .15 * bill;
        }

        JOptionPane.showMessageDialog(null, "Based on your service level, your tip is " + tip);
        System.exit(0);
    }
}