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e920. Appending a Column to a JTable Component

To add a column to a JTable component, the component must use a table model that supports this operation. A simple implementation of such a table model is DefaultTableModel.

The simplest way to add a column to a JTable component using a DefaultTableModel table model is to call DefaultTableModel.addColumn(). You need only supply the name and data for the new column and a new visible column will appear in the table. However, this method of column creation is not suitable after existing columns have undergone customizations or after the user has made adjustments to the existing columns. All customizations and adjustments are lost after the new column is added. For example, if you've installed a special renderer on one of the columns or if the user has moved a column, all these changes will be lost when the new column is added. In fact, if you remove a column (but did not remove the column data), the column will reappear after the new column is added.

This example provides a routine that will add a column without affecting the state of the existing columns. In order for the routine to work, the autoCreateColumnsFromModel property must be set to false. This property causes the table component to rebuild all the columns when a column is added to the table model. When set to false, the table component will no longer add a visible column when a column is added to the table model. This step must now be done explicitly.

    DefaultTableModel model = new DefaultTableModel();
    JTable table = new JTable(model);
    
    // Add a column using the simple method
    model.addColumn("Col1");
    
    // Add a column with values.
    // The list of values are appended to the end of the
    // existing rows. However, if there are more column values
    // than there are rows, new rows with null values are
    // created to accommodate the extra column values.
    model.addColumn("Col2", new Object[]{"v2"});
    // there is now 1 row with 2 columns
    
    // Disable autoCreateColumnsFromModel
    table.setAutoCreateColumnsFromModel(false);
    
    // Add a column without affecting existing columns
    betterAddColumn(table, "Col3", new Object[]{"v3"});
    
    // This method adds a new column to table without reconstructing
    // all the other columns.
    public void betterAddColumn(JTable table, Object headerLabel,
                                Object[] values) {
        DefaultTableModel model = (DefaultTableModel)table.getModel();
        TableColumn col = new TableColumn(model.getColumnCount());
    
        // Ensure that auto-create is off
        if (table.getAutoCreateColumnsFromModel()) {
            throw new IllegalStateException();
        }
        col.setHeaderValue(headerLabel);
        table.addColumn(col);
        model.addColumn(headerLabel.toString(), values);
    }