How To Know If Cell Was Changed In Tableviewer

I created tableviewer ( jface ). All the columns are editable ( using EditingSupport )

I want to know when cell is changed and then to raise a flag in other column. meaning that you start to write any data in the cell. I know that I need to create event of key changed listener to the cells. ( or there is different way )

How I can have access to the cell ? where do I need to add the event

public class MyGridViewer extends TableViewer {
public MyGridViewer (Composite parent) {
super(parent, SWT.MULTI | SWT.H_SCROLL | SWT.V_SCROLL | SWT.FULL_SELECTION | SWT.BORDER);
final Table table = this.getTable();
table.setHeaderVisible(true);
table.setLinesVisible(true);

[Code] ....