Since java.sql.Date extends java.util.Date, you can assign it directly to a java.util.Date. Given two Dates (either type), use getTime() to get a long integer representing the number of milliseconds since January 1st, 1970. Subtract one from the other and divide by 1000 * 60 * 60 * 24 for the number of days between them.
All of this information and more is in the
JavaDocs. They are extremely useful, and
you should get proficient at using them. You'll be able to get answers to some of your questions more quickly than waiting for a reply.