NullPointerException bei getText()

[jnsce]

Hallo, mit ActionListener bekomme ich hier eine Fehlermeldung:

import java.awt.event.*;
import java.awt.*;
import javax.swing.*;
import java.util.*;

public class Test extends JFrame implements ActionListener
{
    private JButton bStart;
    private JTextField tFeld;

    public Test()
    {
        //JFrame
        JFrame JFrame = new JFrame();
        JFrame.setSize(140,100);

        //Panel
        JPanel panel = new JPanel(null);
        panel.setPreferredSize(new Dimension(140,100));
       
        //Startknopf
        bStart = new JButton("Start");
        bStart.setBounds(20,60,100,30);
        bStart.setVisible(true);
        bStart.addActionListener(this);
       
        //Textfeld
        JTextField tFeld = new JTextField("2");
        tFeld.setBounds(20,20,100,20);
        tFeld.setVisible(true);
       
        //Bedienelemente werden panel hinzugefügt
        panel.add(bStart);
        panel.add(tFeld);

        //Panel
        this.add(panel);
        this.pack();
        this.setVisible(true);
    }

    public void actionPerformed (ActionEvent e) {
        //Ausgeben des Inhalts des Textfeldes (bei Drücken des JButtons bStart)
        if (e.getSource() == this.bStart)  
        {
            System.out.println(tFeld.getText());
        }
    }
}

Wenn ich die Methode actionPerformed(ActionEvent e) entferne, den Befehl
in den Konstruktor schreibe und den eventListener entferne, klappt's.
Woran könnte es liegen?

Fehlermeldung:
(46: System.out.println(tFeld.getText()); )

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
   at Test.actionPerformed(Test.java:46)
   at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
   at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2346)
   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:6525)
   at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
   at java.awt.Component.processEvent(Component.java:6290)
   at java.awt.Container.processEvent(Container.java:2234)
   at java.awt.Component.dispatchEventImpl(Component.java:4881)
   at java.awt.Container.dispatchEventImpl(Container.java:2292)
   at java.awt.Component.dispatchEvent(Component.java:4703)
   at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4898)
   at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4533)
   at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4462)
   at java.awt.Container.dispatchEventImpl(Container.java:2278)
   at java.awt.Window.dispatchEventImpl(Window.java:2750)
   at java.awt.Component.dispatchEvent(Component.java:4703)
   at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:751)
   at java.awt.EventQueue.access$500(EventQueue.java:97)
   at java.awt.EventQueue$3.run(EventQueue.java:702)
   at java.awt.EventQueue$3.run(EventQueue.java:696)
   at java.security.AccessController.doPrivileged(Native Method)
   at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
   at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
   at java.awt.EventQueue$4.run(EventQueue.java:724)
   at java.awt.EventQueue$4.run(EventQueue.java:722)
   at java.security.AccessController.doPrivileged(Native Method)
   at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
   at java.awt.EventQueue.dispatchEvent(EventQueue.java:721)
   at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
   at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
   at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
   at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

 

[thecain]

Lies dich mal zum Thema Scope ein. Du erstellst ein neues tField im Konstruktor

 

[Thallius]

Daran das du den Unterschied zwischen lokaler- und Instanzvariable nich kennst...

 

[JCODA]

Ändere
JTextField tFeld =new JTextField("2");
zu
tFeld =new JTextField("2");

du überschreibst die Instanzvariable.