我正在写一个家庭作业的程序，除了一个项目（除了屏幕的实际“视图”显示不佳）之外，它已经完成大部分工作。我正在使用文本字段和组合框基于用户输入进行一些计算。我已将任何文本转换为整数。问题是，当我点击提交按钮时，它应该进行计算，然后显示结果。程序首次打开时，结果显示0.任何帮助将不胜感激。它确实编译没有错误，并将运行。这是我的代码：
import javax.swing.JOptionPane;
import java.awt.*;
import java.awt.event.*;
import java.awt.Graphics.*;
import java.awt.Font.*;
import javax.swing.*;
import javax.swing.text.*;
public class tripManager extends JFrame implements ActionListener
{
//declare variables
Color teal = new Color(0,128,128);
Color wheat = new Color(245,222,179);
Font myFont = new Font("Arial", Font.BOLD,14);
Font titleFont = new Font("Arial",Font.BOLD, 20);
private int oGallons;
private double oPerMileGas;
private int oRefuel;
private int oOilChange;
private double oTotalTripCost;
private int oVehicle;
private int oCMileage;
private int oOMileage;
private double oGasType;
private double oGasCost;
private int oMiles;
private double oOilCost;
//construct components
JPanel titleJPanel = new JPanel();
JLabel companyJLabel = new JLabel("TRAVELOR'S GASOLINE CALCULATOR");
JLabel companyAddressJLabel = new JLabel("11333 Main Street, Zephyrhills, FL 33542");
JLabel descriptionJLabel = new JLabel("Welcome to the Travelor's Gasoline Calculator. This application");
JLabel descriptionJLabel2 = new JLabel("will calculate the total cost of your trip, breaking it down by");
JLabel descriptionJLabel3 = new JLabel("cost per mile and maintenance costs.");
JPanel inputJPanel = new JPanel();
JLabel milesTravelJLabel = new JLabel("Enter total number of trip miles: ");
TextField tripMiles = new TextField(8);
JLabel currentMileageJLabel = new JLabel("Enter current mileage on your vehicle: ");
TextField cMileage = new TextField(8);
JLabel oilChangeMileageJLabel = new JLabel("Enter mileage of last oil change: ");
TextField oMileage = new TextField(8);
JPanel buttonPanel = new JPanel();
Button clearButton = new Button("Clear");
Button submitButton = new Button("Submit");
Button quitButton = new Button("Exit");
JPanel outputPanel = new JPanel();
JLabel gallonsUsedLabel = new JLabel("Total Gallons of gas needed for trip: "+ oGallons+" Gallons");
JLabel costPerMileLabel = new JLabel("Total cost of gas per mile: $"+oPerMileGas);
JLabel refuelLabel = new JLabel("Total number of times to refuel: "+oRefuel);
JLabel oilChangesNeedLabel = new JLabel("Total number of oil changes needed: "+oOilChange);
JLabel totalCostLabel = new JLabel("Total travel cost is: $"+oTotalTripCost);
//construct drop box
JPanel dropJPanel = new JPanel();
JComboBox vehicleCombo = new JComboBox();
JComboBox beginLocation = new JComboBox();
JComboBox endLocation = new JComboBox();
JComboBox gasType = new JComboBox();
public tripManager()
{
//set layouts for frame and panels
this.setLayout(new BorderLayout());
titleJPanel.setLayout(new GridLayout(5,1));
inputJPanel.setLayout(new FlowLayout());
outputPanel.setLayout(new GridLayout(1,5));
dropJPanel.setLayout(new GridLayout(1,4));
buttonPanel.setLayout(new GridLayout(1,3));
//add components to titleJPanel
titleJPanel.add(companyJLabel);
titleJPanel.add(companyAddressJLabel);
titleJPanel.add(descriptionJLabel);
titleJPanel.add(descriptionJLabel2);
titleJPanel.add(descriptionJLabel3);
//add components to inputJPanel
inputJPanel.add(milesTravelJLabel);
inputJPanel.add(tripMiles);
inputJPanel.add(currentMileageJLabel);
inputJPanel.add(cMileage);
inputJPanel.add(oilChangeMileageJLabel);
inputJPanel.add(oMileage);
//add components to output Panel
outputPanel.add(gallonsUsedLabel);
outputPanel.add(costPerMileLabel);
outputPanel.add(refuelLabel);
outputPanel.add(oilChangesNeedLabel);
outputPanel.add(totalCostLabel);
//add components to button Panel
buttonPanel.add(clearButton);
buttonPanel.add(submitButton);
buttonPanel.add(quitButton);
//populate JCombo Boxes
vehicleCombo.addItem("compact");
vehicleCombo.addItem("mid");
vehicleCombo.addItem("luxury");
vehicleCombo.addItem("SUV");
vehicleCombo.addActionListener(this);
vehicleCombo.setToolTipText("Click the drop-down arrow to display list of vehicles");
beginLocation.addItem("New York City");
beginLocation.addItem("Seatle");
beginLocation.addItem("Los Angelos");
beginLocation.addItem("Chicago");
beginLocation.addItem("Atlanta");
beginLocation.addItem("Tampa");
beginLocation.setToolTipText("Click the drop-down arrow to display list of cities");
beginLocation.addItem("New York City");
endLocation.addItem("Seatle");
endLocation.addItem("Los Angelos");
endLocation.addItem("Chicago");
endLocation.addItem("Atlanta");
endLocation.addItem("Tampa");
endLocation.setToolTipText("Click the drop-down arrow to display list of cities");
gasType.addItem("leaded");
gasType.addItem("unleaded");
gasType.addItem("super unleaded");
gasType.addItem("diesel");
gasType.setToolTipText("Click the drop-down arrow to display list of gas types");
//add components to dropPanel
dropJPanel.add(vehicleCombo);
dropJPanel.add(beginLocation);
dropJPanel.add(endLocation);
dropJPanel.add(gasType);
//add panels to frame
add(titleJPanel, BorderLayout.NORTH);
add(inputJPanel, BorderLayout.CENTER);
add(dropJPanel,BorderLayout.EAST);
add(outputPanel, BorderLayout.SOUTH);
add(buttonPanel, BorderLayout.WEST);
//initiate buttons
clearButton.addActionListener(this);
submitButton.addActionListener(this);
quitButton.addActionListener(this);
//add action listener to combo boxes
vehicleCombo.addActionListener(this);
beginLocation.addActionListener(this);
endLocation.addActionListener(this);
gasType.addActionListener(this);
}
public static void main(String[] args)
{
tripManager f = new tripManager();
f.setBounds(400,400,600,600);
f.setTitle("TRAVELOR'S GASOLINE CALCULATOR");
f.setVisible(true);
}//end of main
public void actionPerformed(ActionEvent e)
{
if(e.getSource()==clearButton)
{
tripMiles.setText("");
cMileage.setText("");
oMileage.setText("");
tripMiles.requestFocus();
}
else if(e.getSource()==submitButton)
{
String arg = e.getActionCommand();
if (arg=="submit")
{
//vehicle combo selections
if (arg =="compact")
oVehicle = 13;
else if (arg=="mid")
oVehicle = 18;
else if (arg=="luxury")
oVehicle = 15;
else if (arg == "SUV")
oVehicle = 23;
//gas type combo selections
if (arg =="leaded")
oGasType = 2.50;
else if (arg == "unleaded")
oGasType = 2.90;
else if (arg == "super unleaded")
oGasType = 3.00;
else if (arg == "diesel")
oGasType = 4.00;
//get number of miles
oMiles = Integer.parseInt(tripMiles.getText());
oGasCost = ((oMiles/oVehicle) * oGasType);
//calcculate gallons used
oGallons = oMiles/oVehicle;
//calculate cost per mile
oPerMileGas = oGasCost/oMiles;
//calculate number times to refuel
oRefuel = oGallons/oVehicle;
//calculate oil changes needed
if ((oCMileage - oOMileage)+oMiles >3000)
{
oOilChange = (oCMileage-oOMileage+oMiles)/3000;
}
else
{
oOilChange = 0;
}
oOilCost = oOilChange * 30;
//calculate total trip cost
oTotalTripCost = oOilCost * oGasCost;
Component outputPanel = new JPanel();
JLabel gallonsUsedLabel = new JLabel("Total Gallons of gas needed for trip: " +oGallons+" Gallons");
JLabel costPerMileLabel = new JLabel("Total cost of gas per mile: $"+oPerMileGas);
JLabel refuelLabel = new JLabel("Total number of times to refuel: "+oRefuel);
JLabel oilChangesNeedLabel = new JLabel("Total number of oil changes needed: "+oOilChange);
JLabel totalCostLabel = new JLabel("Total travel cost is: $"+oTotalTripCost);
}
答案 0 :(得分：2)
不要使用==来比较字符串，因为它会检查不是您想要的对象标识。请改用equals(...)或equalsIgnoreCase(...)方法。此外，您无需检查任何JComboBox。 arg String与组合框无关，而是按下按钮的文本，虽然重要的是告诉你什么组合框项目没有被选中。检查每个组合框中的选定项目。如果您对这一点感到困惑，请查看组合框教程。