Got it solved after few hours of experiment. Here is the code for a complete MouseMotionListener. Just added this to the chartPanel and voila! - it works!
The chartY returns proper value of Y-Axis and the dateString returns complete date. Tried it in an OHLC Chart and seems proper.
MouseMotionListener mouselisten = new MouseMotionListener() {
public void mouseDragged(MouseEvent e) {
//
}
public void mouseMoved(MouseEvent e) {
Point2D p = e.getPoint();
Rectangle2D plotArea = chartPanel.getScreenDataArea();
XYPlot plot = (XYPlot) chart.getPlot(); // your plot
double chartX = plot.getDomainAxis().java2DToValue(p.getX(), plotArea, plot.getDomainAxisEdge());
double chartY = plot.getRangeAxis().java2DToValue(p.getY(), plotArea, plot.getRangeAxisEdge());
DecimalFormat dfT = new DecimalFormat("00");
GregorianCalendar gc = new GregorianCalendar();
long lDte = (long)chartX;
Date dtXX = new Date(lDte);
gc.setTime(dtXX);
String sDD = dfT.format(Double.valueOf(String.valueOf(gc.get(GregorianCalendar.DAY_OF_MONTH))));
String sMM = dfT.format(Double.valueOf(String.valueOf(gc.get(GregorianCalendar.MONTH)+1)));
String sYY = dfT.format(Double.valueOf(String.valueOf(gc.get(GregorianCalendar.YEAR))));
String dateString = sDD +"/"+ sMM +"/"+ sYY;
}
};