how to pick a date from calendar in selenium code example

Example: date picker in selenium

Some date pickers allow you to type. In this case we can 
just use sendKeys method to enter the date we want.

If that does not work, we need to write our logic 
for this using java and selenium. 
1. Click on the field to trigger the date picker
2. Get the displayed date on the date picker and calculate
how many times you need to click left/right
to go to the right month/year. 
3. Once we go to the correct month/year, select the date.