Hi anurag,
you asked me some time ago, for a hint how to change the tooltip text in a pie chart (in another posting but this was also concerning other topics so I start a new one...).
Sorry I didn't respond earlier, but had much to do in the last few days.
I actually changed the tooltiptext of a bar chart, but maybe changing it for a pie chart is the same way to do it.
First overwrite the StandardCategoryToolTipGenerator and change the tooltip in the generator's generateToolTip(...) - method.
Then get the renderer for your piechart and set its tooltip generator to an object of your customized StandardCategoryToolTipGenerator.
That's all there is to do.
Regards,
Lisa