Wrapper classes are used to convert any data type into an object.
a wrapper class gets enclose around a data type and appears as an object.

for example: int k = 100; Integer it1 = new Integer(k);
The int data type k is converted into an object, it1 using Integer class.
to unwrap the object it1.
int m = it1.intValue(); System.out.println(m*m); // prints 10000

And now some programs

(1) Wrapper class Example: Primitive to Wrapper:

public class WrapperExample1{  
public static void main(String args[]){  
//Converting int into Integer  
int a=20;  
Integer i=Integer.valueOf(a); 
Integer j=a;  

System.out.println(a+" "+i+" "+j);  
}}  

OUPUT
20 20 20
(2) Wrapper class Example: Wrapper to Primitive:

public class WrapperExample2{    
public static void main(String args[]){    
//Converting Integer to int    
Integer a=new Integer(3);    
int i=a.intValue();
int j=a;
System.out.println(a+" "+i+" "+j);    
}}    
<b>OUPUT</b><br/>

3 3 3