How to generate a Jlist with alternating colors

Question

In Java how do I get a JList with alternating colors? Any sample code?

Anestassia

Answer 1

To customize the look of a JList cells you need to write your own implementation of a ListCellRenderer.

A sample implementation of the class may look like this: (rough sketch, not tested)

public class MyListCellThing extends JLabel implements ListCellRenderer {

    public MyListCellThing() {
        setOpaque(true);
    }

    public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
        // Assumes the stuff in the list has a pretty toString
        setText(value.toString());

        // based on the index you set the color.  This produces the every other effect.
        if (index % 2 == 0) setBackground(Color.RED);
        else setBackground(Color.BLUE);

        return this;
    }
}

To use this renderer, in your JList's constructor put this code:

setCellRenderer(new MyListCellThing());

To change the behavior of the cell based on selected and has focus, use the provided boolean values.

Doublecross

Careful, you need to handle the case where the row is selected (color changes then) – Oceangoing

yeah, I mentioned that in the bottom of the post. – Doublecross

Minor nitpick: should be setBackground rather than setBackgroundColor. – Carrico

I would strongly recommend you extend DefaultListCellRenderer rather than implementing the interface directly. See #3270523. – Duarte

@DuncanJones do you know what you gain by doing that? – Doublecross

I've found that it avoids the issue of having to hand-code the correct behavior when the item is selected. The default class will automatically do what's correct for the current look and feel. – Duarte

+1 for the setCellRenderer() tip. I was extending JList and trying to use my new class instead of JList<String>. All I needed to do was set the renderer to a custom one. Thanks. – Alikee

While extending DefaultListCellRenderer has the benefit of dealing with reasonable UI defaults, it should be noted that DefaultListCellRenderer is not generic / type safe. One has to chose, either UI defaults, or generics. – Geraldo