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Language: Java
Expertise: Intermediate

Mar 27, 2000

If you have a JTable where the values displayed in a particular column are Integer objects, it will display the Integer values with commas (e.g. 98765432 is displayed as 98,765,432) if these two conditions are true:

1. The getColumnClass(int columnIndex) method of the JTable's TableModel returns Integer.class for the column in which the Integer objects are displayed.

2. The JTable is using an instance of javax.swing.table.DefaultTableCellRenderer to display the Integer values.

Under normal circumstances, the second condition is usually true. As its name implies, DefaultTableCellRenderer is the default renderer a JTable uses to display values if another rendederer is not explicitly specified.

The first condition may or may not be true, depending on the TableModel used by the JTable. If an instance of DefaultTableModel is being used, its getColumnClass() method will always return Object.class, and the DefaultTableCellRenderer, having no way of knowing that the Objects it is displaying are actually numeric values, will simply display those objects by calling their toString() method. For Integer objects, toString() returns a String representation of the Integer's value that does not include commas.

Sometimes, the desired behavior might be for the TableModel's getColumnClass() method to return Integer.class—this is important if the table is to be sorted on an Integer column—but the JTable should display Integers without commas. The way to do this is to tell the JTable to use something other than DefaultTableCellRenderer for displaying Integers.

Writing a custom implementation of the TableCellRenderer interface is not trivial, however. The easy solution is to create a subclass of DefaultTableCellRenderer that displays Integers without commas, and lets its parent class handle details like cell background colors, borders, etc. This small class fills the bill:

 
import javax.swing.table.*;
import javax.swing.*;

public class NoCommaIntegerRenderer extends DefaultTableCellRenderer {

    public NoCommaIntegerRenderer() {

        // make sure numbers are displayed right-justified
        setHorizontalAlignment(JLabel.RIGHT);
    } 

    // this overrides setValue() in the parent class.
    public void setValue(Object value) {
        if(value == null) setText("");
        else setText(value.toString());
    }
}

A JTable named "jtable" can use this class to display Integers by
adding the following line of code:

    jtable.setDefaultRenderer(Integer.class, 
                             new NoCommaIntegerRenderer());

By using this solution, a sortable JTable can still sort properly on an Integer column—100 will appear after 20 in an ascending sort, instead of before, which is the case if the values are treated as Objects or Strings—while at the same time, the undesired behavior—the formatting of Integer values with commas—is eliminated.