Question

I really dont even know what to ask but to post the code and to put the error message here. The program should make a window with two tabs and a table of scores in each tab.

package components;

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

public class TopLevelDemo extends JPanel{
    public TopLevelDemo() {
        JTabbedPane tabbedPane = new JTabbedPane();
        String[] players = new String[4];
        Object[][] singlesScores = new Object[2][4];
        Object[][] doublesScores = new Object[2][4];
        createScores(singlesScores);
        createScores(doublesScores);

        JComponent panel1 = makeScoreTable(singlesScores, players, 0, 0);
        tabbedPane.addTab("Singles",panel1);
        tabbedPane.setMnemonicAt(0, KeyEvent.VK_1);

        JComponent panel2 = makeScoreTable(doublesScores, players, 0, 0);
        tabbedPane.addTab("Doubles", panel2);
        tabbedPane.setMnemonicAt(1, KeyEvent.VK_2);

        add(tabbedPane);
        tabbedPane.setTabLayoutPolicy(JTabbedPane.SCROLL_TAB_LAYOUT);
    }
    protected JComponent makeScoreTable(Object[][] scores, String[] players, int x, int y) {
        JPanel panel = new JPanel(true);
        JTable table = new JTable(scores, players);
        GridBagConstraints c = new GridBagConstraints();
        c.gridx=x;
        c.gridy=y;
        panel.add(table, c);
        return panel;
    }
    protected JComponent makeTextPanel(String text) {
        JPanel panel = new JPanel(true);
        JLabel filler = new JLabel(text);
        filler.setHorizontalAlignment(JLabel.CENTER);
        panel.setLayout(new GridLayout(10, 25));
        panel.add(filler);
        return panel;
    }
    private static void createAndShowGUI() {
        JFrame frame = new JFrame("TopLevelDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.add(new TopLevelDemo(), BorderLayout.CENTER);
        frame.pack();
        frame.setVisible(true);
    }
     private Object[][] createScores(Object[][] scores) {
        scores[0][0]= new String("Home");
        scores[0][1]= new Integer(0);
        scores[0][2]= new Integer(0);
        scores[0][3]= new Integer(0);
        scores[1][0]= new String("Away");
        scores[0][1]= new Integer(0);
        scores[0][2]= new Integer(0);
        scores[0][3]= new Integer(0);
        return scores;
    }
    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                UIManager.put("swing.boldMetal", Boolean.FALSE);
                createAndShowGUI();
            }
        });
    }
}

And then i get the error

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at javax.swing.JTable$1.getColumnName(JTable.java:665)
    at javax.swing.JTable.addColumn(JTable.java:2770)
    at javax.swing.JTable.createDefaultColumnsFromModel(JTable.java:1264)
    at javax.swing.JTable.tableChanged(JTable.java:4374)
    at javax.swing.JTable.setModel(JTable.java:3676)
    at javax.swing.JTable.<init>(JTable.java:612)
    at javax.swing.JTable.<init>(JTable.java:553)
    at javax.swing.JTable.<init>(JTable.java:664)
    at components.TopLevelDemo.makeScoreTable(TopLevelDemo.java:30)
    at components.TopLevelDemo.<init>(TopLevelDemo.java:17)
    at components.TopLevelDemo.createAndShowGUI(TopLevelDemo.java:49)
    at components.TopLevelDemo.access$000(TopLevelDemo.java:8)
    at components.TopLevelDemo$1.run(TopLevelDemo.java:68)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:666)
    at java.awt.EventQueue.access$400(EventQueue.java:81)
    at java.awt.EventQueue$2.run(EventQueue.java:627)
    at java.awt.EventQueue$2.run(EventQueue.java:625)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:636)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

Anybody have any idea what I did wrong or poorly?

Answer 1

You need to assign values to the table column names.

A string array of

String[] players = new String[4];

creates an an array of 2 Strings each with default value null. You could use:

String[] players = { "Player 1", "Player 2", "Player 3", "Player 4" };

Update:

Adding a JTable directly onto the score panel does not allow all of the client area to be displayed. To fix, you could place it in a JScrollPane:

panel.add(new JScrollPane(table), c);