Search code examples
javaswingnullpointerexceptionjtablejoptionpane

How can I show a JTable in a dialog box in NetBeans?

I have had a few problems trying to get this table to show in NetBeans. Here is the code that I am trying to use. I am aware that the loop is wrong and will fix that at a later date. I get a runtime error with the following code and I can't work it out.

Object[][] data = null;
String[] columnNames = {"Type", "Grade", "Height", "Width", "Length", "Reinforced Bottom", "Reinforced Corners", "Sealable", "Quantity"};

JTable table = new JTable();

public void showTotalOrder(){
    for(int i=0; i<boxes.size(); i++){
        for(int j=0; j<1; j++){
            data[i][j] = boxes.get(i).getName();
            data[i][j+1] = boxes.get(i).getGrade();
            data[i][j+2] = boxes.get(i).getHeight();
            data[i][j+3] = boxes.get(i).getWidth();
            data[i][j+4] = boxes.get(i).getLength();
            data[i][j+5] = boxes.get(i).getReinforcedBottom();
            data[i][j+6] = boxes.get(i).getReinforcedCorners();
            data[i][j+7] = boxes.get(i).getSealable();
            data[i][j+8] = boxes.get(i).getQuantity();

        }
    }

    JOptionPane.showMessageDialog(this, table);
}

I believe the problem is with the last line of this method.

The error i receive is:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
  at coursework.FlexBox.showTotalOrder(FlexBox.java:116)
  at coursework.FlexBox.currentOrderButtonActionPerformed(FlexBox.java:530)
  at coursework.FlexBox.access$300(FlexBox.java:18)
  at coursework.FlexBox$4.actionPerformed(FlexBox.java:435)
  at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
  at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
  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:6516)
  at javax.swing.JComponent.processMouseEvent(JComponent.java:3320)
  at java.awt.Component.processEvent(Component.java:6281)
  at java.awt.Container.processEvent(Container.java:2229)
  at java.awt.Component.dispatchEventImpl(Component.java:4872)
  at java.awt.Container.dispatchEventImpl(Container.java:2287)
  at java.awt.Component.dispatchEvent(Component.java:4698)
  at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
  at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
  at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
  at java.awt.Container.dispatchEventImpl(Container.java:2273)
  at java.awt.Window.dispatchEventImpl(Window.java:2719)
  at java.awt.Component.dispatchEvent(Component.java:4698)
  at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:735)
  at java.awt.EventQueue.access$200(EventQueue.java:103)
  at java.awt.EventQueue$3.run(EventQueue.java:694)
  at java.awt.EventQueue$3.run(EventQueue.java:692)
  at java.security.AccessController.doPrivileged(Native Method)
  at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
  at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
  at java.awt.EventQueue$4.run(EventQueue.java:708)
  at java.awt.EventQueue$4.run(EventQueue.java:706)
  at java.security.AccessController.doPrivileged(Native Method)
  at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
  at java.awt.EventQueue.dispatchEvent(EventQueue.java:705)
  at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
  at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
  at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
  at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
  at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
  at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
Solution

  • I get a runtime error with the following code and I can't work it out.

    Given this stack trace:

    Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at coursework.FlexBox.showTotalOrder(FlexBox.java:116)
    ...

    You get a NullPointerException because of data array is initialized to null:

    Object[][] data = null;

    Please have a read to: