Wrapped Class

wrappers are classes that wrap up primitive values in classes that offer utility methods to manipulate the values. If for example you want to store a set of int values in the elements of a Vector, the values in a Vector must be objects and not primitives. When you want to retrieve the values wrapped up in the Integers that are in the Vector elements you will need to cast the elements back to Integers and then call the toxxValue in order to get back the original number. The following code demonstrates this technique.

import java.util.*;
public class VecNum
{
        public static void main(String argv[])
                {
                        Vector v = new Vector();
                        v.add(new Integer(1));
                        v.add(new Integer(2));
                        for(int i=0; i < v.size();i ++)
                        {
                           Integer iw =(Integer) v.get(i);
                           System.out.println(iw.intValue());
                        }
                }
}


The wrapper classes also offer utility methods for converting to and from the int values they represent. Thus if you have a string that could also represent a number, you can use a wrapper class to perform that calculation
The methods of the wrapper classes are all static so you can use them without creating an instance of the matching wrapper class. Note that once a wrapper has a value assigned to it that value cannot be changed.


See more details here.