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.
Explicit closing of the ResultSet and Statement is the preferred way to go. This let's the database server free its resources. If you close the Connection w/out closing the ResultSet, your Java resources are freed, but the database may still consider the ResultSet (cursor) to be open. I've seen this lead to a "Maximum number of cursors exceeded" error.