This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
You will also need Calendar.setTime(). If you look at the Java API documentation, you can easily find answers to such questions on your own with a little bit of effort. I strongly suggest that you follow the above link and find the docs for the version of Java that you are using. Being able to navigate the Java API docs is an essential skill when programming in Java, imo.
Originally posted by bijoy bose: but i have a specific date in hand say Date e = 11/01/00; now i have to add 90 days to it and find out which day it will be??
Help is available in the first article (Calculating Java Dates) I suggested above. A direct quote from the article: "Also, you will see how to do elementary calculations with dates, such as calculating the date 90 days after another date." Sounds exactly like what you want to do. We can (and will) point you in the right direction, but no one here is going to do the work for you. You will not learn how to program if we did.
I also agree with Layne that learning how to read and extract things from the API docs is an essential skill. Those docs may seem a little daunting at first, but after a bit of time they become much easier to understand.