2 Replies Latest reply: Apr 15, 2007 5:28 PM by 807606 RSS

    Exception in thread "main" java.lang.NullPointerException

    807606
      import java.awt.Container;
      import java.awt.event.ActionEvent;
      import java.awt.event.ActionListener;
      import javax.swing.*;
      /*
       * UserInterface.java
       * @author tristan
       * Created on April 15, 2007, 5:45 PM
       */
      
      public class UserInterface extends JFrame implements ActionListener {
          //Declare member variables
          private JLabel monthLabel = new JLabel();
          private JTextField month = new JTextField();
          private JLabel dayLabel = new JLabel();
          private JTextField day = new JTextField();
          private JLabel yearLabel = new JLabel();
          private JTextField year = new JTextField();
          //CalendarManager
          private JTextArea entry = new JTextArea();
          private JButton saveEntry;
          private JButton getEntry;
          
          public UserInterface() {
              //... Build the content pane.
              Container content = this.getContentPane();
              content.add(monthLabel); // Add components to the content
              content.add(month);
              content.add(dayLabel);
              content.add(day);
              content.add(yearLabel);
              content.add(year);
              content.add(entry);
              content.add(saveEntry);
              content.add(getEntry);
              
              this.setTitle("Calendar Program");
              this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
              this.pack();   // does layout of components.
          }//end constructor
      
      public static void main(String[] args) {
          JFrame window = new UserInterface();
          window.setVisible(true);
      }
      
          public void actionPerformed(ActionEvent e) {
          }
      }
      I've never had this happen before. Why am I getting a null exception? The full error is:
      Exception in thread "main" java.lang.NullPointerException
              at java.awt.Container.addImpl(Container.java:1027)
              at java.awt.Container.add(Container.java:352)
              at UserInterface.<init>(UserInterface.java:34)
              at UserInterface.main(UserInterface.java:55)