Advanced understanding of JTables

[Matt Kurz]

1.) The following leads to index out of bounds. But not if I do also: tableModel.addColumn(column1); tableModel.addColumn(column2); Why?
Does that mean I have to register the TableColumns on the model, too? I thought initializing the JTable with the TableColumnModel would be enough.

tableModel = new DefaultTableModel();
DefaultTableColumnModel tableColumnModel = new DefaultTableColumnModel();
TableColumn column1 = new TableColumn(0);
column1.setHeaderValue("ModulName");
TableColumn column2 = new TableColumn(1);
column2.setHeaderValue("Description");
tableColumnModel.addColumn(column1);
tableColumnModel.addColumn(column2);
JTable table = new JTable(tableModel, tableColumnModel);
tableModel.addRow(new String[]{rs.getString("ModulName"), rs.getString("Description")});

2.) How can I change the column width? I tried:

        tableColumnModel.getColumn(0).setPreferredWidth(50);
        tableModel.fireTableStructureChanged();

and

        table.getColumn("ModulName").setPreferredWidth(40);
        tableModel.fireTableStructureChanged();

But that does not schow a change. Why? And how have to do it?

[Rob Spoor]

Your TableModel has 0 columns and 0 rows, yet when you connect it all by creating the JTable your TableColumnModel expects two columns.

[Matt Kurz]

Rob Prime wrote:Your TableModel has 0 columns and 0 rows, yet when you connect it all by creating the JTable your TableColumnModel expects two columns.

Would you please explain what you mean? I have no idea.

[Rob Spoor]

Matt Kurz wrote:

tableModel = new DefaultTableModel();

Here you create a TableModel with 0 columns and 0 rows. In other words, it's completely empty.

TableColumn column1 = new TableColumn(0);
column1.setHeaderValue("ModulName");
TableColumn column2 = new TableColumn(1);
column2.setHeaderValue("Description");

Here you create two TableColumn objects, one for the first column and one for the second.

JTable table = new JTable(tableModel, tableColumnModel);

Your table now has two columns. Its model still has 0 columns. The table tries to get the model's values for columns 0 and 1 (because they are present in the TableColumnModel) but there are no such columns in the model. Hence the exception.

[Matt Kurz]

Understood. Thanks! I already read about deviding between data and it's presentation, but I need some practice. How can I change the column width? I tried:

        tableModel = new DefaultTableModel();
        DefaultTableColumnModel tableColumnModel = new DefaultTableColumnModel();
        TableColumn column1 = new TableColumn(0);
        column1.setHeaderValue("ModulName");
        TableColumn column2 = new TableColumn(1);
        column2.setHeaderValue("Description");
        tableColumnModel.addColumn(column1);
        tableColumnModel.addColumn(column2);
        tableModel.addColumn(column1);
        tableModel.addColumn(column2);
        
        JTable table = new JTable(tableModel, tableColumnModel);
        column1.setWidth(40);
        tableColumnModel.getColumn(0).setWidth(40);
        table.getColumnModel().getColumn(0).setWidth(40);
        table.getColumn("ModulName").setWidth(40);

I also tried table.repaint() table.revalidate, fire..., but nothing changed.

Edit: Here it looks easy: example But I do not see, why it does not work in my case.

[Rob Spoor]

The auto resize mode is turned to off in that example.

[Matt Kurz]

Rob Prime wrote:The auto resize mode is turned to off in that example.

Yes, I know. I also tried around that. For instance:

        table.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);
        column1.setWidth(40);  
        column2.setWidth(200);  

But both columns always have the same width. Would you please show a working example, and explain why all my tries did not work. And in which cases can I expect what from all these variants.

Edit: Ok now I found a working example.

        table.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);
        column1.setPreferredWidth(200);
        column2.setPreferredWidth(800);

But I have not understood much.

Edit2:
This works too, but the interpretation of the integers is different with setAutoResizeMode on:

        table.getColumn("ModulName").setPreferredWidth(200);
        table.getColumn("Description").setPreferredWidth(800);

[Martijn van der Geest]

Try the following:

Create a new class and let the class extend DefaultTableModel.
Implement the method getColumnCount and return 2.
Implement the method getColumnName and return the correct name for the index. (ModuleName for index 0 etc.)
Implement other required methods.

Create your JTable based on your custom tablemodel class instance.
Use table.getColumnModel().getColumn(index).setWidth(width) or play around a bit with other width possibilities. (like setPrefferedWidth).

Not sure if this fixes your problem but it at least improves your code since jtable is based on the model/view principle.