我是Java的新手，我得到一个空指针异常。我知道它发生在哪里但无法确定原因。它位于下面的代码部分。该代码正在验证时间工资和工资和时间的格式。
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at javagui.enterButtonActionPerformed(javagui.java:167)
at javagui$1.actionPerformed(javagui.java:86)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:723)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:682)
at java.awt.EventQueue$3.run(EventQueue.java:680)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:696)
at java.awt.EventQueue$4.run(EventQueue.java:694)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:693)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)
这是代码： -
import java.awt.Component;
import java.text.DecimalFormat;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
/**
*
* @author Andy
*/
public class javagui extends javax.swing.JPanel {
private JLabel tutorTimeLabel;
private JLabel paymentLabel;
private JScrollPane jScrollPane1;
private JTextArea reportTextArea;
private JTextField tutorTime;
private JTextField payment;
private JButton enterButton;
private JButton reportButton;
private JButton quitButton;
private Component paymentText;
private Component tutorTimeText;
//2d array
double[][] timeWage;
//position in array
int timeWageIndex = 0;
//minimum wage
double minimumWage = 6.55;
static final String lineSeparator = System.getProperty("line.separator");
/** Creates new form GUI */
public javagui() {
initComponents();
}
/** This method is called from within the constructor to
* initialize the form.
* WARNING: Do NOT modify this code. The content of this method is
* always regenerated by the Form Editor.
*/
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {
tutorTimeLabel = new javax.swing.JLabel();
paymentLabel = new javax.swing.JLabel();
jScrollPane1 = new javax.swing.JScrollPane();
reportTextArea = new javax.swing.JTextArea();
tutorTimeText = new javax.swing.JTextField();
paymentText = new javax.swing.JTextField();
enterButton = new javax.swing.JButton();
reportButton = new javax.swing.JButton();
quitButton = new javax.swing.JButton();
tutorTimeLabel.setText("Enter total tutoring time in minutes:");
paymentLabel.setText("Enter total amount earned this session:");
reportTextArea.setColumns(20);
reportTextArea.setRows(5);
jScrollPane1.setViewportView(reportTextArea);
enterButton.setText("Enter");
enterButton.addActionListener(new java.awt.event.ActionListener() {
@Override
public void actionPerformed(java.awt.event.ActionEvent evt) {
enterButtonActionPerformed(evt);
}
});
reportButton.setText("Report");
reportButton.addActionListener(new java.awt.event.ActionListener() {
@Override
public void actionPerformed(java.awt.event.ActionEvent evt) {
reportButtonActionPerformed(evt);
}
});
quitButton.setText("Quit");
quitButton.addActionListener(new java.awt.event.ActionListener() {
@Override
public void actionPerformed(java.awt.event.ActionEvent evt) {
quitButtonActionPerformed(evt);
}
});
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(this);
this.setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(23, 23, 23)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 434, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
.addComponent(enterButton, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(reportButton, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(quitButton, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)))
.addGroup(layout.createSequentialGroup()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING, false)
.addComponent(tutorTimeLabel, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(paymentLabel, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
.addGap(18, 18, 18)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
.addComponent(paymentText)
.addComponent(tutorTimeText, javax.swing.GroupLayout.DEFAULT_SIZE, 120, Short.MAX_VALUE))))
.addContainerGap(58, Short.MAX_VALUE))
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addComponent(tutorTimeText, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGroup(layout.createSequentialGroup()
.addGap(24, 24, 24)
.addComponent(tutorTimeLabel)))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(paymentLabel)
.addComponent(paymentText, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGap(18, 18, 18)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addComponent(enterButton)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
.addComponent(reportButton)
.addGap(18, 18, 18)
.addComponent(quitButton)
.addContainerGap(320, Short.MAX_VALUE))
.addComponent(jScrollPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 426, Short.MAX_VALUE)))
);
}// </editor-fold>
public void quitButtonActionPerformed(java.awt.event.ActionEvent evt) {
//select to close the Calculator
System.exit(0);
}
public void reportButtonActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
reportTextArea.setText(""); // clear previous report
String newline = "\n";
double timeTotal = 0;
double wageTotal = 0;
//Loops through each entry
for(int i = 0; i<=timeWageIndex-1; i++){
//Gets current entry time
double time = timeWage[i][0];
//Gets current entry wage
double wage = timeWage[i][1];
//Adds to sums
timeTotal += time;
wageTotal += wage;
reportTextArea.append("Minutes = " + time + " Earnings = $" + wage + newline);
}
DecimalFormat df = new DecimalFormat("#.##");
double average = wageTotal / (timeTotal/60);
//Displays report
reportTextArea.append(newline + newline + "*****************************" + newline + newline + newline);
reportTextArea.append("Report of your wages to Date:" + newline + newline);
reportTextArea.append("Total Minutes Spent Tutoring = " + timeTotal + newline);
reportTextArea.append("Total Earnings = $" + wageTotal + newline);
reportTextArea.append("Average Per Hour Wage = $" + df.format(average) + newline + newline);
reportTextArea.append("Minimum Wage is currently: $" + minimumWage + newline);
if(average<minimumWage) {
reportTextArea.append("Your average wages are less than average");
}
else if(average>minimumWage && average < minimumWage*2.0) {
reportTextArea.append("Your average wages are average");
}
else if(average >= minimumWage*2.0) {
reportTextArea.append("Your average wages are above average");
}
}
public void enterButtonActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
//Code Exception error messages when data keyed incorrectly for both textfields
double time = 0;
double wage = 0;
//Validates time
try {
time = Double.parseDouble(tutorTime.getText());
} catch (NumberFormatException e1) {
JOptionPane.showMessageDialog(null, "The time must be a decimal number", "Invalid Input",JOptionPane.ERROR_MESSAGE);
}
//Validate wage
try {
wage = Double.parseDouble(payment.getText());
} catch (NumberFormatException e1) {
JOptionPane.showMessageDialog(null, "The wage must be a decimal number", "Invalid Input",JOptionPane.ERROR_MESSAGE);
}
//Time greater than 0 and less than 4 hours
if(time<=0 || time>240){
JOptionPane.showMessageDialog(null, "The time must greater than 0 and less than or equal to 4 hours (240 min)",
"Invalid Input",JOptionPane.ERROR_MESSAGE);
}
else{
//Wage greater than 0
if(wage<=0){
JOptionPane.showMessageDialog(null, "The wage must greater than 0",
"Invalid Input",JOptionPane.ERROR_MESSAGE);
}
else{
//update array values
timeWage[timeWageIndex][0] = time;
timeWage[timeWageIndex][1] = wage;
//increment index
timeWageIndex++;
//Reset text for user entry
tutorTime.setText("");
payment.setText("");
}
}
}
}
答案 0 :(得分：1)
定义了这两个文本字段：
private JTextField tutorTime;
private JTextField payment;
但是，它们未初始化，而是在面板中初始化并使用这两个：
private Component paymentText;
private Component tutorTimeText;
但是，在enterButtonActionPerformed中，tutorTime和payment的引用为null，这些调用会产生NullPointerException。两次修复，将tutorTime的引用替换为tutorTimeText。 payment也是如此。不确定为什么这些字段被定义为Component，因此您需要转换为JTextField，即：
time = Double.parseDouble(((JTextField) tutorTimeText).getText());
另请注意，timeWage数组也未初始化，接下来您将需要处理另一个NullPointerException。