JTextField Dilemma??

Question

I am a beginner Java program. I have made a screen using swing. It has three panels on a frame and laid out using different layouts.
Now a button is clicked on one panel and I want it to clear all the JTextFields in another panel.
I have an ActionListener for the button and am using JTextField.setText("") .
It throws an exception:
"Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException"
Why would this happen?
Also the same thing happens when I try a button to get the data from these JTextFields using JtextField.getText();
Do I have to implement ActionListener or DocumentListener for JTextFields also?
Thanks.

Answer 1

Maybe I should give some of my code to make my problem clear.
public class InputFrame extends JFrame {
     public InputFrame(){
          setTitle("Input Screen");
          setSize(500,400);
          JPanel p1=new JPanel();
          p1.setLayout(new BoxLayout(p1,BoxLayout.Y_AXIS));
          JPanel plr=new JPanel();
          plr.setBorder(new EtchedBorder());
          plr.setLayout(new GridLayout(5,2,5,5));
          plr.add(new JLabel());
          plr.add(new JLabel("Date (yyyy-mm-dd)"));
          JTextField dtField=new JTextField("",1);
          plr.add(dtField);
          plr.add(new JLabel());
          plr.add(new JLabel());
          plr.add(new JLabel("Category"));
          JTextField catField=new JTextField("",1);
          plr.add(catField);
          plr.add(new JLabel());
          p1.add(plr);
          getContentPane().add(p1,BorderLayout.CENTER);
          JPanel p2=new JPanel();
          p2.setLayout(new BoxLayout(p2,BoxLayout.Y_AXIS));
          p2.setBorder(new EtchedBorder());
          p2.add(new JLabel("Choose the check-boxes and then enter the required data."));
          p2.add(new JLabel("If the check-boxes are not clicked, then that data will not be considered."));
          getContentPane().add(p2,BorderLayout.NORTH);
          JPanel p3=new JPanel();
          p3.setLayout(new BoxLayout(p3,BoxLayout.X_AXIS));
          p3.setBorder(new EtchedBorder());
          p3.add(new JLabel(" "));
          JButton MainButton=new JButton("Main Menu");
          p3.add(MainButton);
          JButton ClearButton=new JButton("Clear Data");
          p3.add(ClearButton);
          MainButton.addActionListener(m);
          ClearButton.addActionListener(c);
          getContentPane().add(p3,BorderLayout.SOUTH);
     }//end constructor
     //listener for main button
     ActionListener m=new ActionListener(){
          public void actionPerformed(ActionEvent e){
               //open main screen
               MainFrame mframe=new MainFrame();
               mframe.setVisible(true);
               dispose();
//TODO:listener for clear button-THIS IS WHERE THE ERROR OCCURS!
     ActionListener c=new ActionListener(){
          public void actionPerformed(ActionEvent evt){
               //clear all the fields
               dtField.setText(" ");
               catField.setText(" ");
               accnoField.setText(" ");
               accnameField.setText(" ");
               amtField.setText(" ");
               dispose();
     private JButton MainButton;
     private JButton ClearButton;
     private JButton SaveButton;
     private JButton ExitButton;
     private JTextField dtField;
     private JTextField catField;
     private JTextField accnoField;
     private JTextField accnameField;
     private JTextField amtField;
     public static void main(String[] args) {
          // TODO Auto-generated method stub
          JFrame frame1 = new InputFrame();
          frame1.setVisible(true);
          frame1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
So I am trying to click a button and clear out the text fields. But its giving me errors. Any ideas why?
Thanks.