为什么我的程序在textfields保持空白时崩溃？

Question

我有这个学校的程序，它填写所有的文本字段时工作正常。但是，如果在字段中留下任何空白，整个程序将崩溃。这里是我的代码：

/** Kyle N Welch 
    * Sept 29th, 2017 
    * This program will calculate the expanses of a business 
    * man/woman on a business trip using the GUI 
    * */ 

import java.awt.*; 
import java.awt.event.*; 
import javax.swing.*; 
import java.text.DecimalFormat; 

//Class name declaration 
public class KNW_TravelExpenses extends JFrame 
{ 
    private JPanel travelInfoPanel; 
    private JPanel buttonPanel; 

    // Labels 
    private JLabel numDaysOnTripLabel; 
    private JLabel amountAirfairLabel; 
    private JLabel amountCarRentalLabel; 
    private JLabel milesDrivenLabel; 
    private JLabel parkingFeesLabel; 
    private JLabel taxiFeesLabel; 
    private JLabel confRegLabel; 
    private JLabel lodgingChargesPerNightLabel; 

    // Text Fields 
    private JTextField numDaysOnTripTextField; 
    private JTextField amountAirfairTextField; 
    private JTextField amountCarRentalTextField; 
    private JTextField milesDrivenTextField; 
    private JTextField parkingFeesTextField; 
    private JTextField taxiFeesTextField; 
    private JTextField confRegTextField; 
    private JTextField lodgingChargesPerNightTextField; 

    // Buttons 
    private JButton resetButton; 
    private JButton calcButton; 

    // Meals amount reimbursed by company per day. 
    private double mealsAmount = 37.00; 

    // Parking Fees amount reimbursed by company per day. 
    private double parkingFeesReimbursed = 10.00; 

    // Taxi Charges amount reimbursed by company per day. 
    private double taxiChargesReimbursed = 20.00; 

    // Lodging Charges amount reimbursed by company per day. 
    private double lodgingChargesReimbursed = 95.00; 

    // Private Vehicle per miles reimbursment rate. 
    private double prVechiclePerMileReimbursed = 0.27; 

    // Constructor 
    public KNW_TravelExpenses() 
    { 
    //set the title. 
    super("TRAVEL EXPENSES"); 
    // Set the main window 
    setLocationRelativeTo(null); 
    // Specify an action for the close button. 
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    // Create a BorderLayout manager for the content pane. 
    setLayout(new BorderLayout()); 
    // Build the TravelInfo and Buttons panels 
    buildTravelInfoPanel(); 
    buildButtonPanel(); 
    // Add the panels to the frame's content pane 
    add(travelInfoPanel, BorderLayout.CENTER); 
    add(buttonPanel, BorderLayout.SOUTH); 
    // Pack the contents of the window and display it. 
    pack(); 
    setVisible(true); 
    } 
    // The buildTravelInfoPanel method adds the labels 
    //and text fiels to the TravelInfo panel. 
    private void buildTravelInfoPanel() 
    { 
    // Create the labels for TravelInfo fields 
    numDaysOnTripLabel = new JLabel("Number of days on trip: "); 
    amountAirfairLabel = new JLabel("Amount of airfair: "); 
    amountCarRentalLabel = new JLabel("Amount of car rental fees: "); 
    milesDrivenLabel = new JLabel("Number of Miles driven: "); 
    parkingFeesLabel = new JLabel("Amount of Parking fees: "); 
    taxiFeesLabel = new JLabel("Amount of Tax charges: "); 
    confRegLabel = new JLabel("Conference or Seminar registration fees: "); 
    lodgingChargesPerNightLabel = new JLabel("Lodging charges per night: "); 
    // Create the text boxes for TravelInfo user input 
    numDaysOnTripTextField = new JTextField(3); 
    amountAirfairTextField = new JTextField(8); 
    amountCarRentalTextField = new JTextField(8); 
    milesDrivenTextField = new JTextField(4); 
    parkingFeesTextField = new JTextField(6); 
    taxiFeesTextField = new JTextField(6); 
    confRegTextField = new JTextField(8); 
    lodgingChargesPerNightTextField = new JTextField(6); 
    // Create a panel to hold labels and text fields. 
    travelInfoPanel = new JPanel(); 
    // Create GridLayout manager 
    travelInfoPanel.setLayout(new GridLayout(10, 2)); 
    // Add the labels and text fields to this panel. 
    travelInfoPanel.add(numDaysOnTripLabel); 
    travelInfoPanel.add(numDaysOnTripTextField); 
    travelInfoPanel.add(amountAirfairLabel); 
    travelInfoPanel.add(amountAirfairTextField); 
    travelInfoPanel.add(amountCarRentalLabel); 
    travelInfoPanel.add(amountCarRentalTextField); 
    travelInfoPanel.add(milesDrivenLabel); 
    travelInfoPanel.add(milesDrivenTextField); 
    travelInfoPanel.add(parkingFeesLabel); 
    travelInfoPanel.add(parkingFeesTextField); 
    travelInfoPanel.add(taxiFeesLabel); 
    travelInfoPanel.add(taxiFeesTextField); 
    travelInfoPanel.add(confRegLabel); 
    travelInfoPanel.add(confRegTextField); 
    travelInfoPanel.add(lodgingChargesPerNightLabel); 
    travelInfoPanel.add(lodgingChargesPerNightTextField); 
    // Add an empty border around the panel for spacing. 
    travelInfoPanel.setBorder(BorderFactory.createEmptyBorder(10, 10, 1, 10)); 
    } 

    /*** The buildButtonPanel method creates and adds the Reset and Calculate 
    * buttons to the TravelExpense panel as its own panel. 
    */ 
    private void buildButtonPanel() 
    { 
    // Create the calcButton. 
    calcButton = new JButton("CALCULATE"); 

    // Register an event listener 
    calcButton.addActionListener(new CalcButtonListener()); 

    //Create the resetButton. 
    resetButton = new JButton("RESET"); 

    // Create the Buttons panels. 
    buttonPanel = new JPanel(); 

    buttonPanel.setLayout(new BorderLayout(5, 5)); 

    buttonPanel.add(resetButton, BorderLayout.WEST); 
    buttonPanel.add(calcButton, BorderLayout.CENTER); 

    //Add an empty border around the panel for spacing. 
    buttonPanel.setBorder(BorderFactory.createEmptyBorder(1, 10, 10, 10)); 
    } 

    /** Private inner class that handles the event when the user clicks 
    * the Calculate button . 
    */ 
    private class CalcButtonListener implements ActionListener 
    { 
    // Declare variables 
    String input; 
    int days; 
    double air; 
    double carRental; 
    double miles; 
    double parking; 
    double taxi; 
    double confReg; 
    double lodging; 
    double mealsAmount; 

    public void actionPerformed(ActionEvent e) 
    { 
     //Declare variables 
     double actualExpenses; 
     double milesExpenses; 
     double allowableExpenses; 
     double excessAir; 
     double excessCarRental; 
     double excessParking; 
     double excessTaxi; 
     double excessLodging; 
     double excessAmountTotal; 
     double amountSaved=0; 
     double paidBackAmount=0; 

     //Create a DecimalFormat object to format the totals as dollar amounts. 
     DecimalFormat dollar = new DecimalFormat("$#,##0.00"); 

     //Get Input Data the user entered in the text fields. 
     days = Integer.parseInt(numDaysOnTripTextField.getText()); 
     air = Double.parseDouble(amountAirfairTextField.getText()); 
     carRental = Double.parseDouble(amountCarRentalTextField.getText()); 
     miles = Double.parseDouble(milesDrivenTextField.getText()); 
     parking = Double.parseDouble(parkingFeesTextField.getText()); 
     taxi = Double.parseDouble(taxiFeesTextField.getText()); 
     confReg = Double.parseDouble(confRegTextField.getText()); 
     lodging = Double.parseDouble(lodgingChargesPerNightTextField.getText()); 

     //Determine actualExpenses method. 
     milesExpenses = miles * prVechiclePerMileReimbursed; 
     actualExpenses = (carRental + parking + taxi + lodging +mealsAmount) 
     *days+air+milesExpenses+ confReg ; 

     // Calculate the allowableExpenses. 
     allowableExpenses=(mealsAmount+parkingFeesReimbursed+taxiChargesReimbursed+lodgingChargesReimbursed) 
     *days+milesExpenses+air+confReg; 

     // Calculate the paidBackAmount. 
     if(actualExpenses>allowableExpenses) 
     paidBackAmount=actualExpenses-allowableExpenses; 
     else 
     amountSaved=allowableExpenses-actualExpenses; 

     // Display the Totals message box. 
     if(paidBackAmount>0) 
     JOptionPane.showMessageDialog(null, "Total expenses: " 
             + dollar.format(actualExpenses) +"\n" +"Allowable expenses: " 
             + dollar.format(allowableExpenses)+"\n" +"\n" + "Amount to be paid back: " 
             +dollar.format(paidBackAmount)); 
     else if(amountSaved>0) 
     JOptionPane.showMessageDialog(null, "Total expenses: " + dollar.format(actualExpenses) 
             +"\n" +"Allowable expenses: " + dollar.format(allowableExpenses)+"\n" + 
             "\n" + "Amount Saved: "+dollar.format(amountSaved)); 
     else 
     JOptionPane.showMessageDialog(null, "Total expenses: " + dollar.format(actualExpenses) 
             +"\n" +"Allowable expenses: " + dollar.format(allowableExpenses)+"\n"); 
    } 
    } 

    /*** Private inner class that handles the event when the user clicks 
    * the RESET button . 
    */ 
    private class ResetButtonListener implements ActionListener 
    { 
    public void actionPerformed(ActionEvent e) 
    { 
     numDaysOnTripTextField.setText(" "); 
     amountAirfairTextField.setText(" "); 
     amountCarRentalTextField.setText(" "); 
     milesDrivenTextField.setText(" "); 
     parkingFeesTextField.setText(" "); 
     taxiFeesTextField.setText(" "); 
     confRegTextField.setText(" "); 
     lodgingChargesPerNightTextField.setText(" "); 
    } 
    } 
// The main method 
    public static void main(String[] args) 
    { 
    new TravelExpenses(); 
    } 
} 

任何可能导致GUI程序崩溃时字段留空。必须有一些东西，我明显错过了它。如果你能指出我的意见并告诉我它是如何修复的，任何帮助都将不胜感激。

Answer 1

尝试try-catch当您使用parseInt，因为它提高FormatException（试图parseInt从null字符串可以以崩溃结束）。

Answer 2

最有可能的是，错误发生的原因是您尝试将空字符串视为数字。程序是否应该处理丢失的数据？如果是的话，你必须修改你的计算，或者将空白视为零或以其他方式处理。

重要的一课是查看堆栈跟踪。 Java会告诉你究竟是哪里和哪里出了问题。正如其他人所说的，要么将程序减少到最小程度，这样我们就不必猜测，或提供堆栈跟踪。