Primitive data types :
They are not objects according to the compiler, it cannot treat like objects.
You cannot extend from the class int because it does not exist.
Object-oriented programmers not accept. Everything must be an object.
So, Java includes wrapper classes which convert the primitive data types into real Java Objects.
There is no class in Java called int but there is a class called Integer.
Java is case-sensitive, so Integer does not equal int.
Java provides the Collections Framework. In the Collection Framework,
a collection represents the group of the objects.so,primitive data not treat as Object.
It cannot store in Collection and after wrapper the primitive data types store in the Collection.
For example :
public static void main(String args)
ArrayList al =new ArrayList();
al.add(new Integer(i)); // wrapper the int "i".
System.out.println("ArrayList : " + al);
For read more on Collection to visit the link....http://www.roseindia.net/java/example/java/util/