0
我想構建一個簡單的Java GUI（我只學了一個星期）。我創建了一個Textfield，用戶必須輸入一個數字。我想用數字做一些事情，但現在的問題是，當我調用方法textfield.getText（）時，我得到一個'空指針除外。在文檔中說它可以在底層文檔爲空時得到異常。我不知道什麼是「未定文件」是。Java，什麼是底層文檔
任何幫助？ 代碼：
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.BadLocationException;
import java.awt.*;
import java.awt.event.*;
public class GUI extends JFrame {
String [] aFull1 = new String [500];
String [] aFull2 = new String [500];
String [] aFull3 = new String [500];
String [] aFull4 = new String [500];
String [] aList1 = new String [15];
String [] aList2 = new String [15];
String [] aList3 = new String [15];
String [] aList4 = new String [15];
int pop1 = 0;
int pop2 = 0;
int pop3 = 0;
int pop4 = 0;
//JTextField tfNr = new JTextField();
JTextField tfNr = new JTextField ("");
JButton bStart = new JButton ("Start");
JButton bPause = new JButton ("Pause");
JButton bStop = new JButton ("Stop");
JList lList1 = new JList (aList1);
JList lList2 = new JList (aList2);
JList lList3 = new JList (aList3);
JList lList4 = new JList (aList4);
JButton bOK = new JButton ("OK");
JButton bRemove = new JButton ("Remove last item");
JTextArea taTijd = new JTextArea ("00:00:00", 10, 4);
JPanel panel = new JPanel();
Timer timer = new Timer(1000, new ActionListener() {
public void actionPerformed (ActionEvent e){
time++;
dispTime(); }}
);
final JTextArea taStrtNr = new JTextArea ("Voer startnummer in:");
static int time = 0;
static int pTime;
GUI() {
// Set title //
super ("Ultraloop");
addToWindow();
setPos();
setProperties();
// Add ActionListeners //
handler HO = new handler();
bStart.addActionListener(HO);
bPause.addActionListener(HO);
bStop.addActionListener(HO);
bOK.addActionListener(HO);
/*for (int i = 0; i<100; i++){
addOne(1,"One");
}
addOne(1,"Two");
scrollDown(1);
addOne(1,"One");
addOne(2,"Two");
addOne(3,"Three");
addOne(4,"Four");*/
// Final add //
add(panel);
}
private class handler implements ActionListener {
public void actionPerformed (ActionEvent e){
if (e.getSource()==bStart){
if (!timer.isRunning()){
timer.start();
}
}
else if (e.getSource() == bPause){
if (timer.isRunning()){
pTime = time;
timer.stop();
}
else if (pTime != 0){
timer.start();
time = pTime;
}
}
else if (e.getSource() == bStop){
if (timer.isRunning()){
timer.stop();
time = 0;
dispTime();
}
}
else if (e.getSource() == bOK){
try {
if (tfNr.getDocument().getText(0,2) != null){
addOne(Integer.getInteger(tfNr.getDocument().getText(0,2)));
}
} catch (BadLocationException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
}
}
private void addToWindow(){
add(tfNr);
add(bStart);
add(bPause);
add(bStop);
add(lList1);
add(lList2);
add(lList3);
add(lList4);
add(bOK);
add(bRemove);
add(taTijd);
add(taStrtNr);
}
private void setPos() {
tfNr.setBounds(20,25, 75,25);
bStart.setBounds(500,255, 75,25);
bPause.setBounds(500,290, 75,25);
bStop.setBounds(500,325, 75,25);
lList1.setBounds(20,75, 60,272);
lList2.setBounds(80,75, 50,272);
lList3.setBounds(130,75, 150,272);
lList4.setBounds(280,75, 150,272);
bOK.setBounds(110, 25, 75, 25);
bRemove.setBounds(80,20, 150,20);
taTijd.setBounds(445,10, 150,50);
taStrtNr.setBounds(20, 5, 150, 25);
}
private void setProperties() {
// Set Editable //
taTijd.setEditable(false);
taStrtNr.setEditable(false);
// Set Font //
taTijd.setFont(new Font("Arial", Font.BOLD + Font.ITALIC, 28));
bRemove.setFont (new Font("Arial", Font.PLAIN, 12));
// Set List properties //
lList1.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
lList2.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
lList3.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
lList4.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
lList1.setVisibleRowCount(15);
lList2.setVisibleRowCount(15);
lList3.setVisibleRowCount(15);
lList4.setVisibleRowCount(15);
lList1.setBorder(BorderFactory.createLineBorder(Color.black));
lList2.setBorder(BorderFactory.createLineBorder(Color.black));
lList3.setBorder(BorderFactory.createLineBorder(Color.black));
lList4.setBorder(BorderFactory.createLineBorder(Color.black));
lList1.setBackground(new Color(180,180,180));
lList2.setBackground(new Color(180,180,180));
lList3.setBackground(new Color(180,180,180));
lList4.setBackground(new Color(180,180,180));
panel.setBackground(Color.WHITE);
tfNr.setBackground(new Color(230,230,230));
tfNr.setBorder(BorderFactory.createLineBorder(Color.BLACK));
}
private void addOne (int nr) {
System.out.print(String.format("%d",nr));
}
private void removeOne(){
}
private void dispTime() {
int h, m, s;
h = time/3600;
m = (time%3600)/60;
s = ((time%3600)%60);
taTijd.setText(String.format("%02d:%02d:%02d",h,m,s));
}
private void scrollDown (int a) {
}
}
發佈異常的* complete *堆棧跟蹤。告訴我們'Textfield'的完整類名（提示：'tfNr.getClass（）。getCanonicalName（）'）。並告訴我們你的代碼片段在哪一行開始。 – 2011-04-16 12:43:09
爲了更快地獲得更好的幫助，請發佈[SSCCE]（http://pscode.org/sscce.html）。 – 2011-04-16 13:29:00
順便說一句 - J2SE中沒有'Textfield'。你的意思是1）'TextField' 2）'JTextField'（正如'swing'標籤所暗示的那樣）3）第三方'Textfield'？ – 2011-04-16 13:31:31