table rendering problem
messageTable =new JTable(model){
public Class getColumnClass(int column)
{
return getValueAt(0, column).getClass();
}
public Component prepareRenderer(
TableCellRenderer renderer,int row,int column)
{
Component c = super.prepareRenderer(renderer, row, column);
c.setBackground(Color.GREEN);
//if (isRowSelected(row) && isColumnSelected(column))
//((JComponent)c).setBorder(new LineBorder(Color.red));
return c;
}
};
xception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at MailClient$1.getColumnClass(MailClient.java:177)
at javax.swing.JTable.getCellRenderer(Unknown Source)
at javax.swing.plaf.basic.BasicTableUI.paintCell(Unknown Source)
at javax.swing.plaf.basic.BasicTableUI.paintCells(Unknown Source)
at javax.swing.plaf.basic.BasicTableUI.paint(Unknown Source)
at javax.swing.plaf.ComponentUI.update(Unknown Source)
at javax.swing.JComponent.paintComponent(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.s/.........................................
reason behind exception not able to find please help
thank you
sumant
# 1
reason behind exception not able to find please help
Well, the message "java.lang.NullPointerException at MailClient$1.getColumnClass(MailClient.java:177)" pretty obviously means that a reference which you are accessing on line 177 of MailClient.java is null.
Which means that one of your cell values (as returned by getValue()) is null.
Your getColumnClass() implemention is poor anyway: as we can see it doesn't cope with nulls, but it will also break through polymorphism. Let's say one of the columns contains Numbers (some Integers, some Doubles, some Longs)... using your implementation, you can never return the Number class, it will only return the actual class of the first element, so your method cannot describe the widest class of value in that column and you will have values which are not castable to the reported class.
# 6
> I removed first method and it's working fine now
Thats not the way to problem solve. If you don't know what the method does, then why are you using it.
The method is important because the table uses it to determine what renderer and editor to use for the given column of data. I guess if all your data is a String then its not that important, but you should understand what it does, before removing it.
The problem with the code is that you have a null value in the TableModel. So is this a valid situation. If not, then fix the problem with the bad data.
If a null is a valid value, then here is an example of a getColumnClass(..) method implementation:
public Class getColumnClass(int column)
{
for (int row = 0; row < getRowCount(); row++)
{
Object o = getValueAt(row, column);
if (o != null)
return o.getClass();
}
return Object.class;
}
