Grid - CheckBox render

I changed the column render to use a custom render with checkbox.
The result is the column show the word “true” or “false” when not editable mode and when I make the grid editable, the checkbox are showed.
I like do the checkbox visible independent the grid is editable or not.

My render is:
public class BooleanRenderer extends AbstractRenderer {
public BooleanRenderer() {

Someone can help?