Java5 Autoboxing & Unboxing

As any Java programmer knows, you can't put an int (or other primitive value) into a collection. Collections can only hold object references, so you have to box primitive values into the appropriate wrapper class (which is Integer in the case of int). When you take the object out of the collection, you get the Integer that you put in; if you need an int, you must unbox the Integer using the intValuemethod. All of this boxing and unboxing is a pain, and clutters up your code. The autoboxing and unboxing feature automates the process, eliminating the pain and the clutter.

http://download.oracle.com/javase/1.5.0/docs/guide/language/autoboxing.html