First problem GUI fixed just some math problems

Question

Well the titles says everything =) I believe my math is wrong a little( maybe its not  could you test and see if its correct) and I want to round the numbers to 2 decimals places. THat's the problem: Create a GUI application that calculates and displays the total travel expenses of a business person on a trip. Here is the information that the user must provide: • Number of days on the trip • Amount of airfare if any •Amount of car rental fees if any • Number of miles driven if a private vehicle was used • Amount of parking fees if any • Amount of taxi charges if any • Conference or seminar registration fees if any Lodging charges per night The company reimburses travel expenses according to the following policy: • $37 per day for meals • Parking fees up to $10.00 per day • Taxi charges up to $20.00 per day • Lodging charges up to $95.00 per day • If a private vehicle is used $0.27 per mile driven import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import javax.swing.*; import java.awt.*; /** * * @author Alexander */ public class Expenses extends JFrame { private final int WIDTH = 500; private final int HEIGHT = 500; JPanel panel = new JPanel(); private JLabel numberOfDaysLabel; private JLabel amountAirfareLabel; private JLabel amontRentalFeeLabel; private JLabel numberMilesLabel; private JLabel parkingFeeLabel; private JLabel taxiFeeLabel; private JLabel seminarFeeLabel; private JLabel lodgingFeeLabel; private JTextField daysField; private JTextField amountAirfareField; private JTextField rentalFeeField; private JTextField milesDrivenField; private JTextField parkingFeeField; private JTextField taxiFeeField; private JTextField smeinarFeeField; private JTextField lodgingFeeField; private JButton calculateButton; public Expenses() { setTitle(Travel Expenses); setSize(WIDTH HEIGHT); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); buildPanel(); add(panel); setVisible(true); } private void buildPanel() { numberOfDaysLabel = new JLabel(Number of days on the trip: ); daysField = new JTextField(10); amountAirfareLabel = new JLabel(Amount of airfare: ); amountAirfareField = new JTextField(10); amontRentalFeeLabel = new JLabel(Amount of car rental fee: ); rentalFeeField = new JTextField(10); numberMilesLabel = new JLabel(Number of miles driven: ); milesDrivenField = new JTextField(10); parkingFeeLabel = new JLabel(Amount of parking fees: ); parkingFeeField = new JTextField(10); taxiFeeLabel = new JLabel(Taxi charges: ); taxiFeeField = new JTextField(10); seminarFeeLabel = new JLabel(Conference or seminar registration fees: ); smeinarFeeField = new JTextField(10); lodgingFeeLabel = new JLabel(Lodging charges per night); lodgingFeeField = new JTextField(10); calculateButton = new JButton(Calculate); calculateButton.addActionListener(new buttonListener()); panel = new JPanel(new GridLayout(9 2 5 10)); panel.add(numberOfDaysLabel); panel.add(daysField); panel.add(amountAirfareLabel); panel.add(amountAirfareField); panel.add(amontRentalFeeLabel); panel.add(rentalFeeField); panel.add(numberMilesLabel); panel.add(milesDrivenField); panel.add(parkingFeeLabel); panel.add(parkingFeeField); panel.add(taxiFeeLabel); panel.add(taxiFeeField); panel.add(seminarFeeLabel); panel.add(smeinarFeeField); panel.add(lodgingFeeLabel); panel.add(lodgingFeeField); panel.add(calculateButton); } public class buttonListener implements ActionListener { public void actionPerformed(ActionEvent e) { String stringDay stringAirfare stringCarRental stringMilesDriven stringParkingFee stringTaxiCharges stringSeminarFee stringLodgingFee; double totalAllowed totalOwe totalSaved totalExpenses numberDays AirFare CarRental MilesDriven ParkingFee TaxiCharges seminarFee lodgingFee; final double dayMeal = 37.00; final double parkingFee = 10.00; final double taxiFee = 20.00; final double lodgingCharge = 95.00; final double rentCar = 0.27; double totalMilesDriven; stringDay = daysField.getText(); numberDays = Double.parseDouble(stringDay); stringAirfare = amountAirfareField.getText(); AirFare = Double.parseDouble(stringAirfare); stringCarRental = rentalFeeField.getText(); CarRental = Double.parseDouble(stringCarRental); stringMilesDriven = milesDrivenField.getText(); MilesDriven = Double.parseDouble(stringMilesDriven); stringParkingFee = parkingFeeField.getText(); ParkingFee = Double.parseDouble(stringParkingFee); stringTaxiCharges = taxiFeeField.getText(); TaxiCharges = Double.parseDouble(stringTaxiCharges); stringSeminarFee = smeinarFeeField.getText(); seminarFee = Double.parseDouble(stringSeminarFee); stringLodgingFee = lodgingFeeField.getText(); lodgingFee = Double.parseDouble(stringLodgingFee); totalMilesDriven = MilesDriven * rentCar; totalExpenses = AirFare * CarRental * MilesDriven * ParkingFee * TaxiCharges * seminarFee * lodgingFee; totalAllowed = numberDays * dayMeal * parkingFee * taxiFee * lodgingCharge * rentCar * totalMilesDriven; if (totalExpenses > totalAllowed) { totalOwe = totalExpenses - totalAllowed; } else { totalOwe = 0; } if (totalAllowed > totalExpenses) { totalSaved = totalAllowed - totalExpenses; } else { totalSaved = 0; } System.out.println(The total expenses for the trip are  + totalExpenses +  
The total allowed to spend is  + totalAllowed + 
The total you owe is  + totalOwe + 
Total saved is  + totalSaved); } } }

Vulpes · Answer

I'm not sure you're going about the calculation the right way. totalMilesDriven is OK. I think you then need another variable for meals and lodging charges which have a fixed daily charge: (meals + lodgings) * days However parking and taxi charges are subject to a maximum daily charge so you need to take into account what was actually spent i.e. parking fees allowed = actual parking fees orif less 10 * days taxi charges allowed = actual taxi charges or if less 20 * days The total travel expenses will then be the sum of all these. To round to 2 dp you can do this: double someNumber = 123.456; // say DecimalFormat df = new DecimalFormat(0.00); String roundedNumber = df.format(someNumber);