This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
You use it exactly as you wrote it. dateString is the date you want to check. If the date can not be converted into a valid date, it throws a parse exception. If you want the date to be in a specific format in order to be determined to be valid then you can use the SimpleDateFormat class to define a format.