Java swing cell renderer based on column class

In Java Swing we have a JTable, TableModel, ColumnModel and a TableCellRenderer which work together to display a table.

How can I provide customisation to get a custom cell renderer based on a column class - as opposed to setting the renderer based on column index.

final JTable table = new JTable(model);
table.getColumnModel().getColumn(0).setCellRenderer(new DateTimeRenderer());
table.getColumnModel().getColumn(1).setCellRenderer(new SuperDuperDoubleCellRenderer());

Suppose I have 20 numeric cells in there!!!

The above works, but I am not so keen on that solution as it would change when the model changed - so it isn't well encapsulated to that extent - this is client code.

The TableModel understands the underlying table data structure where it can do the custom mapping to a complex type (as opposed to DefaultTableModel and Vectors) - where it knows the data types of how each column.

public class DemoTableModel implements TableModel {
    @Override
    public Class<?> getColumnClass(int columnIndex) {
        // date time, double, etc...
        return columnInfo.get(columnIndex).getDataType();
    }
}

What I would like to do is to tell a JTable, hey the column class (returned from the table model) is a custom DateTime type - use the CustomDateTimeCellRenderer. If it is a double, then use the custom SuperDuperDoubleCellRenderer.

The trouble is digging through the sources to see where this behaviour marries up.

> What I would like to do is to tell a JTable, hey the column class (returned from the table model) is a custom DateTime type - use the CustomDateTimeCellRenderer. If it is a double, then use the custom SuperDuperDoubleCellRenderer.

You set the renderer at the table level by specifying the class and renderer:

table.setDefaultRenderer(Double.class, yourDoubleCellRenderer);
table.setDefaultRenderer(CustomDateTime.class, yourCustomDateTimeRenderer);

You can do this at the CellRenderer level - cell renderers are only required to implement

Component getTableCellRendererComponent​(JTable table,
                                    Object value,
                                    boolean isSelected,
                                    boolean hasFocus,
                                    int row,
                                    int column)

Nothing stops you from telling the whole JTable to render cells using a, say, SmartCellRenderer that looks at the type of the passed-in value and delegates actual rendering to a DoubleCellRenderer, a StringCellRenderer, or a CuteInternetCatRenderer. Assuming object types are unique, this should be easy to do (if somewhat ugly because of the set of if (value instanceof InternetCat) { ... } that decides how to render each object based on its class).

A better solution (no ugly instanceofs required) is to assign specific renderers to specific columns at column insertion time:

 // model index 0, width 75, renderer to use, editor to use
 myTable.getColumnModel().addColumn(0, 75, cuteInternetCatRenderer, null);