如何在 Java 中更新使用 NetBeans 图形 GUI 设计器创建的文本字段
How to update Text Field created with NetBeans graphical GUI designer in Java
几十年来我一直在编写嵌入式 C 代码，我希望通过学习 Java 来更新我的技能。
我还需要一个项目的图形测试工具（读取串口、处理数据、根据 GUI 按钮选择将结果写入串口等）
我正在尝试使用 NetBeans 图形 GUI 设计器来创建 GUI，然后添加 Java 代码来实现逻辑，但我仍在学习 Java 所以我不确定如何从 Java 代码访问我的 GUI 中的文本字段。具体来说，我想要一个屏幕上的文本框，它每秒更新一次当前时间（这最终将成为一个健康检查路由，寻找错过的命令超时等）。
我遇到的问题是如何从我的 healthCheck() 例程访问名为 timeDisplayField 的文本字段对象。 healthCheck() 例程每秒都会被调用一次，但是当我取消注释任何试图访问 timeDisplayField 对象的尝试时，我要么得到一个编译错误，要么得到一个 NullPointer 运行 时间错误。
/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package myPackage;
import java.util.Calendar;
import java.util.Timer;
import java.util.TimerTask;
import java.util.Date;
/**
*
* @author SGrunza
*/
public class mainWindow extends javax.swing.JFrame {
/**
* Creates new form mainWindow
*/
public void healthCheck()
{
Calendar now = Calendar.getInstance();
int hour = now.get( Calendar.HOUR_OF_DAY );
int minute = now.get( Calendar.MINUTE );
int second = now.get( Calendar.SECOND );
String timeString = new String();
//System.out.printf("%02d:%02d:%02d\r\n", hour, minute, second );
timeString = timeString.format( "%02d:%02d:%02d\r\n", hour, minute, second );
timeDisplayField.setText( timeString );
}
public mainWindow()
{
Timer healthTimer = new Timer();
healthTimer.scheduleAtFixedRate( new TimerTask()
{
@Override
public void run()
{
//System.out.println( "healthTask " + new Date() +
// "Thread name: " + Thread.currentThread().getName() );
healthCheck();
}
},
0, // delay until first run
1000 ); // delay for each subsequent run
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">//GEN-BEGIN:initComponents
private void initComponents() {
interfaceTypeGroup = new javax.swing.ButtonGroup();
jPanel1 = new javax.swing.JPanel();
nfcButton = new javax.swing.JRadioButton();
smipButton = new javax.swing.JRadioButton();
serialButton = new javax.swing.JRadioButton();
appStatusField = new javax.swing.JTextField();
msgField = new javax.swing.JTextField();
cardReaderStatusField = new javax.swing.JTextField();
timeDisplayField = new javax.swing.JTextField();
activateButton = new javax.swing.JButton();
readButton = new javax.swing.JButton();
deactivateButton = new javax.swing.JButton();
checkSleepButton = new javax.swing.JButton();
getInfoButton = new javax.swing.JButton();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
interfaceTypeGroup.add(nfcButton);
nfcButton.setSelected(true);
nfcButton.setText("NFC");
interfaceTypeGroup.add(smipButton);
smipButton.setForeground(new java.awt.Color(153, 153, 153));
smipButton.setText("SMIP");
interfaceTypeGroup.add(serialButton);
serialButton.setForeground(new java.awt.Color(153, 153, 153));
serialButton.setText("Serial");
appStatusField.setText("appStatus");
msgField.setText("msgWindow");
cardReaderStatusField.setText("cardReader_status");
timeDisplayField.setText("timeDisplay");
activateButton.setLabel("Activate");
readButton.setText("Read Sensor");
deactivateButton.setText("Deactivate");
checkSleepButton.setText("Check Sleep");
getInfoButton.setText("Get Info");
javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
jPanel1.setLayout(jPanel1Layout);
jPanel1Layout.setHorizontalGroup(
jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel1Layout.createSequentialGroup()
.addContainerGap()
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(msgField)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING, false)
.addComponent(activateButton, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(deactivateButton, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(readButton, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
.addGroup(jPanel1Layout.createSequentialGroup()
.addComponent(getInfoButton, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addContainerGap())
.addGroup(jPanel1Layout.createSequentialGroup()
.addComponent(checkSleepButton, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addGap(12, 12, 12))))
.addGroup(jPanel1Layout.createSequentialGroup()
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel1Layout.createSequentialGroup()
.addGap(12, 12, 12)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(nfcButton)
.addComponent(smipButton)
.addComponent(serialButton))
.addGap(18, 18, 18)
.addComponent(cardReaderStatusField))
.addGroup(jPanel1Layout.createSequentialGroup()
.addGap(12, 12, 12)
.addComponent(appStatusField, javax.swing.GroupLayout.PREFERRED_SIZE, 203, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 564, Short.MAX_VALUE)
.addComponent(timeDisplayField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)))
.addGap(12, 12, 12))
);
jPanel1Layout.setVerticalGroup(
jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel1Layout.createSequentialGroup()
.addContainerGap()
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
.addGroup(jPanel1Layout.createSequentialGroup()
.addComponent(nfcButton)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(smipButton)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(serialButton))
.addComponent(cardReaderStatusField))
.addGap(18, 18, 18)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(timeDisplayField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(appStatusField, javax.swing.GroupLayout.PREFERRED_SIZE, 63, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGap(18, 18, 18)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(activateButton)
.addComponent(getInfoButton))
.addGap(18, 18, 18)
.addComponent(readButton)
.addGap(18, 18, 18)
.addComponent(deactivateButton)
.addGap(37, 37, 37)
.addComponent(checkSleepButton)
.addGap(18, 18, 18)
.addComponent(msgField, javax.swing.GroupLayout.DEFAULT_SIZE, 217, Short.MAX_VALUE)
.addContainerGap())
);
timeDisplayField.getAccessibleContext().setAccessibleName("timeDisplayField");
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addContainerGap())
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
);
pack();
}// </editor-fold>//GEN-END:initComponents
/**
* @param args the command line arguments
*/
public static void main(String args[]) {
/* Set the Nimbus look and feel */
//<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
/* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
* For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html
*/
try {
for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
if ("Nimbus".equals(info.getName())) {
javax.swing.UIManager.setLookAndFeel(info.getClassName());
break;
}
}
} catch (ClassNotFoundException ex) {
java.util.logging.Logger.getLogger(mainWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (InstantiationException ex) {
java.util.logging.Logger.getLogger(mainWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
java.util.logging.Logger.getLogger(mainWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (javax.swing.UnsupportedLookAndFeelException ex) {
java.util.logging.Logger.getLogger(mainWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
}
//</editor-fold>
/* Create and display the form */
java.awt.EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
new mainWindow().setVisible(true);
}
});
}
// Variables declaration - do not modify//GEN-BEGIN:variables
public javax.swing.JButton activateButton;
public javax.swing.JTextField appStatusField;
public javax.swing.JTextField cardReaderStatusField;
public javax.swing.JButton checkSleepButton;
public javax.swing.JButton deactivateButton;
public javax.swing.JButton getInfoButton;
public javax.swing.ButtonGroup interfaceTypeGroup;
public javax.swing.JPanel jPanel1;
public javax.swing.JTextField msgField;
public javax.swing.JRadioButton nfcButton;
public javax.swing.JButton readButton;
public javax.swing.JRadioButton serialButton;
public javax.swing.JRadioButton smipButton;
public javax.swing.JTextField timeDisplayField;
// End of variables declaration//GEN-END:variables
}
我是 Java 的新手，所以我不确定到哪里寻求帮助。我怀疑部分问题在于使用 NetBeans GUI 构建器，但我真的不想手动构建所有 GUI。
将其归结为一个简单的问题：如何更改 healthCheck() 以便它更新屏幕上的文本字段？
答案在What is a NullPointerException and how do i fix it. 你可以在stacktrace中看到它（错误）：
Exception in thread "Timer-0" java.lang.NullPointerException
at rae.mainWindow.healthCheck(mainWindow.java:24)
at rae.mainWindow.run(mainWindow.java:35)
at java.util.TimerThread.mainLoop(Timer.java:555)
at java.util.TimerThread.run(Timer.java:505)
在第 24 行，你有这一行：
timeDisplayField.setText(timeString);
timeString 不是 null 这意味着 timeDisplayField 是 null。那是因为您首先启动计时器，然后调用创建文本字段的 initComponents 方法：
public mainWindow() {
Timer healthTimer = new Timer();
healthTimer.scheduleAtFixedRate(new TimerTask() {
@Override
public void run() {
// System.out.println( "healthTask " + new Date() +
// "Thread name: " + Thread.currentThread().getName() );
healthCheck();
}
}, 0, // delay until first run
1000); // delay for each subsequent run
initComponents(); //here
}
您可以通过在时间初始化之前调用 initComponents 来修复它：
public mainWindow() {
Timer healthTimer = new Timer();
initComponents(); //Before timer
healthTimer.scheduleAtFixedRate(new TimerTask() {
@Override
public void run() {
// System.out.println( "healthTask " + new Date() +
// "Thread name: " + Thread.currentThread().getName() );
healthCheck();
}
}, 0, // delay until first run
1000); // delay for each subsequent run
}
但是，不建议在 Swing 环境中使用 java.util.Timer。考虑将其更改为 Swing Timer which is created for such cases. A good example of its usage can be found in
几十年来我一直在编写嵌入式 C 代码，我希望通过学习 Java 来更新我的技能。
我还需要一个项目的图形测试工具（读取串口、处理数据、根据 GUI 按钮选择将结果写入串口等）
我正在尝试使用 NetBeans 图形 GUI 设计器来创建 GUI，然后添加 Java 代码来实现逻辑，但我仍在学习 Java 所以我不确定如何从 Java 代码访问我的 GUI 中的文本字段。具体来说，我想要一个屏幕上的文本框，它每秒更新一次当前时间（这最终将成为一个健康检查路由，寻找错过的命令超时等）。
我遇到的问题是如何从我的 healthCheck() 例程访问名为 timeDisplayField 的文本字段对象。 healthCheck() 例程每秒都会被调用一次，但是当我取消注释任何试图访问 timeDisplayField 对象的尝试时，我要么得到一个编译错误，要么得到一个 NullPointer 运行 时间错误。
/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package myPackage;
import java.util.Calendar;
import java.util.Timer;
import java.util.TimerTask;
import java.util.Date;
/**
*
* @author SGrunza
*/
public class mainWindow extends javax.swing.JFrame {
/**
* Creates new form mainWindow
*/
public void healthCheck()
{
Calendar now = Calendar.getInstance();
int hour = now.get( Calendar.HOUR_OF_DAY );
int minute = now.get( Calendar.MINUTE );
int second = now.get( Calendar.SECOND );
String timeString = new String();
//System.out.printf("%02d:%02d:%02d\r\n", hour, minute, second );
timeString = timeString.format( "%02d:%02d:%02d\r\n", hour, minute, second );
timeDisplayField.setText( timeString );
}
public mainWindow()
{
Timer healthTimer = new Timer();
healthTimer.scheduleAtFixedRate( new TimerTask()
{
@Override
public void run()
{
//System.out.println( "healthTask " + new Date() +
// "Thread name: " + Thread.currentThread().getName() );
healthCheck();
}
},
0, // delay until first run
1000 ); // delay for each subsequent run
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">//GEN-BEGIN:initComponents
private void initComponents() {
interfaceTypeGroup = new javax.swing.ButtonGroup();
jPanel1 = new javax.swing.JPanel();
nfcButton = new javax.swing.JRadioButton();
smipButton = new javax.swing.JRadioButton();
serialButton = new javax.swing.JRadioButton();
appStatusField = new javax.swing.JTextField();
msgField = new javax.swing.JTextField();
cardReaderStatusField = new javax.swing.JTextField();
timeDisplayField = new javax.swing.JTextField();
activateButton = new javax.swing.JButton();
readButton = new javax.swing.JButton();
deactivateButton = new javax.swing.JButton();
checkSleepButton = new javax.swing.JButton();
getInfoButton = new javax.swing.JButton();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
interfaceTypeGroup.add(nfcButton);
nfcButton.setSelected(true);
nfcButton.setText("NFC");
interfaceTypeGroup.add(smipButton);
smipButton.setForeground(new java.awt.Color(153, 153, 153));
smipButton.setText("SMIP");
interfaceTypeGroup.add(serialButton);
serialButton.setForeground(new java.awt.Color(153, 153, 153));
serialButton.setText("Serial");
appStatusField.setText("appStatus");
msgField.setText("msgWindow");
cardReaderStatusField.setText("cardReader_status");
timeDisplayField.setText("timeDisplay");
activateButton.setLabel("Activate");
readButton.setText("Read Sensor");
deactivateButton.setText("Deactivate");
checkSleepButton.setText("Check Sleep");
getInfoButton.setText("Get Info");
javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
jPanel1.setLayout(jPanel1Layout);
jPanel1Layout.setHorizontalGroup(
jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel1Layout.createSequentialGroup()
.addContainerGap()
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(msgField)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING, false)
.addComponent(activateButton, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(deactivateButton, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(readButton, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
.addGroup(jPanel1Layout.createSequentialGroup()
.addComponent(getInfoButton, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addContainerGap())
.addGroup(jPanel1Layout.createSequentialGroup()
.addComponent(checkSleepButton, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addGap(12, 12, 12))))
.addGroup(jPanel1Layout.createSequentialGroup()
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel1Layout.createSequentialGroup()
.addGap(12, 12, 12)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(nfcButton)
.addComponent(smipButton)
.addComponent(serialButton))
.addGap(18, 18, 18)
.addComponent(cardReaderStatusField))
.addGroup(jPanel1Layout.createSequentialGroup()
.addGap(12, 12, 12)
.addComponent(appStatusField, javax.swing.GroupLayout.PREFERRED_SIZE, 203, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 564, Short.MAX_VALUE)
.addComponent(timeDisplayField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)))
.addGap(12, 12, 12))
);
jPanel1Layout.setVerticalGroup(
jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel1Layout.createSequentialGroup()
.addContainerGap()
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
.addGroup(jPanel1Layout.createSequentialGroup()
.addComponent(nfcButton)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(smipButton)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(serialButton))
.addComponent(cardReaderStatusField))
.addGap(18, 18, 18)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(timeDisplayField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(appStatusField, javax.swing.GroupLayout.PREFERRED_SIZE, 63, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGap(18, 18, 18)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(activateButton)
.addComponent(getInfoButton))
.addGap(18, 18, 18)
.addComponent(readButton)
.addGap(18, 18, 18)
.addComponent(deactivateButton)
.addGap(37, 37, 37)
.addComponent(checkSleepButton)
.addGap(18, 18, 18)
.addComponent(msgField, javax.swing.GroupLayout.DEFAULT_SIZE, 217, Short.MAX_VALUE)
.addContainerGap())
);
timeDisplayField.getAccessibleContext().setAccessibleName("timeDisplayField");
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addContainerGap())
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
);
pack();
}// </editor-fold>//GEN-END:initComponents
/**
* @param args the command line arguments
*/
public static void main(String args[]) {
/* Set the Nimbus look and feel */
//<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
/* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
* For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html
*/
try {
for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
if ("Nimbus".equals(info.getName())) {
javax.swing.UIManager.setLookAndFeel(info.getClassName());
break;
}
}
} catch (ClassNotFoundException ex) {
java.util.logging.Logger.getLogger(mainWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (InstantiationException ex) {
java.util.logging.Logger.getLogger(mainWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
java.util.logging.Logger.getLogger(mainWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (javax.swing.UnsupportedLookAndFeelException ex) {
java.util.logging.Logger.getLogger(mainWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
}
//</editor-fold>
/* Create and display the form */
java.awt.EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
new mainWindow().setVisible(true);
}
});
}
// Variables declaration - do not modify//GEN-BEGIN:variables
public javax.swing.JButton activateButton;
public javax.swing.JTextField appStatusField;
public javax.swing.JTextField cardReaderStatusField;
public javax.swing.JButton checkSleepButton;
public javax.swing.JButton deactivateButton;
public javax.swing.JButton getInfoButton;
public javax.swing.ButtonGroup interfaceTypeGroup;
public javax.swing.JPanel jPanel1;
public javax.swing.JTextField msgField;
public javax.swing.JRadioButton nfcButton;
public javax.swing.JButton readButton;
public javax.swing.JRadioButton serialButton;
public javax.swing.JRadioButton smipButton;
public javax.swing.JTextField timeDisplayField;
// End of variables declaration//GEN-END:variables
}
我是 Java 的新手，所以我不确定到哪里寻求帮助。我怀疑部分问题在于使用 NetBeans GUI 构建器，但我真的不想手动构建所有 GUI。
将其归结为一个简单的问题：如何更改 healthCheck() 以便它更新屏幕上的文本字段？
答案在What is a NullPointerException and how do i fix it. 你可以在stacktrace中看到它（错误）：
Exception in thread "Timer-0" java.lang.NullPointerException
at rae.mainWindow.healthCheck(mainWindow.java:24)
at rae.mainWindow.run(mainWindow.java:35)
at java.util.TimerThread.mainLoop(Timer.java:555)
at java.util.TimerThread.run(Timer.java:505)
在第 24 行，你有这一行：
timeDisplayField.setText(timeString);
timeString 不是 null 这意味着 timeDisplayField 是 null。那是因为您首先启动计时器，然后调用创建文本字段的 initComponents 方法：
public mainWindow() {
Timer healthTimer = new Timer();
healthTimer.scheduleAtFixedRate(new TimerTask() {
@Override
public void run() {
// System.out.println( "healthTask " + new Date() +
// "Thread name: " + Thread.currentThread().getName() );
healthCheck();
}
}, 0, // delay until first run
1000); // delay for each subsequent run
initComponents(); //here
}
您可以通过在时间初始化之前调用 initComponents 来修复它：
public mainWindow() {
Timer healthTimer = new Timer();
initComponents(); //Before timer
healthTimer.scheduleAtFixedRate(new TimerTask() {
@Override
public void run() {
// System.out.println( "healthTask " + new Date() +
// "Thread name: " + Thread.currentThread().getName() );
healthCheck();
}
}, 0, // delay until first run
1000); // delay for each subsequent run
}
但是，不建议在 Swing 环境中使用 java.util.Timer。考虑将其更改为 Swing Timer which is created for such cases. A good example of its usage can be found in