SwingSet2 JTable Demo throws NullPointerException

Name: dk106046 Date: 02/17/2003

In the JTable demo, if I double click on the first cell in the Favorite Number column, delete the value and click on some
other cell, a java.lang.NullPointerException is getting thrown.
*****************************************************************************************************************************

java.lang.NullPointerException
        at TableDemo$10.getColumnClass(TableDemo.java:498)
        at javax.swing.JTable.getColumnClass(JTable.java:1762)
        at javax.swing.JTable.getCellRenderer(JTable.java:3683)
        at javax.swing.plaf.basic.BasicTableUI.paintCell(BasicTableUI.java:1177)

        at javax.swing.plaf.basic.BasicTableUI.paintCells(BasicTableUI.java:1080
)
        at javax.swing.plaf.basic.BasicTableUI.paint(BasicTableUI.java:1003)
        at javax.swing.plaf.ComponentUI.update(ComponentUI.java:162)
        at javax.swing.JComponent.paintComponent(JComponent.java:566)
        at javax.swing.JComponent.paint(JComponent.java:833)
        at javax.swing.JComponent.paintWithOffscreenBuffer(JComponent.java:4885)

        at javax.swing.JComponent.paintDoubleBuffered(JComponent.java:4838)
        at javax.swing.JComponent._paintImmediately(JComponent.java:4782)
        at javax.swing.JComponent.paintImmediately(JComponent.java:4591)
        at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:430)

        at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(System
EventQueueUtilities.java:137)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:204)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:526)
        at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchTh
read.java:237)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThre
ad.java:181)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:175)

        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:167)

        at java.awt.EventDispatchThread.run(EventDispatchThread.java:130)
*****************************************************************************************************************************
 
Expected Result
The exception should not get thrown.

Steps to Recreate:
1) cd to \Java141\demo\jfc\SwingSet2
2) enter appletviewer SwingSet2.html
3) Select the JTable demo
4) Double click on the first cell in the Favorite Number column. Delete the value. Click on another cell.

For empty cells, getValueAt(row, col) method returns null and hence getColumnClass() method
in TableDemo throws NPE.
I can think of two fixes for this bug.

1) ----------------------

    public Class getColumnClass(int c)
    {
        Object obj = null;
        for (int i=0; i<getRowCount(); i++)
        {
            obj=getValueAt(i, c);
            if(obj!=null) return obj.getClass();
        }
        return Object.class;
    }
------------------------

2)---------------------
    public Class getColumnClass(int c)
    {
        return c==4 ? Double.class : getValueAt(0, c).getClass();
    }
-----------------------
I am going for fix 2, as 5th column (ie. c=4) will be always Double.

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