its a class used to convert primitive data type to user 
defined data type like Integer

for example 

public class WrapperSample1 
{
   public static void main (String args[])
   {
      int iVal = 100;
      long lVal = 200;
      float fVal = 300;
      double dVal = 400;

      String str = "123";

      //primitive types to corresponding wrapper objects
      Integer intVal = Integer.valueOf(iVal);
      Long lgVal = Long.valueOf(lVal);
      Double dbVal = Double.valueOf(dVal);
      Float ftVal = Float.valueOf(fVal);

      //primitive types to string objects
      str = String.valueOf(iVal);
      str = String.valueOf(lVal);
      str = String.valueOf(fVal);
      str = String.valueOf(dVal);

      //wrapper Objects to corresponding primitive types
      iVal = intVal.intValue();
      lVal = lgVal.longValue();
      fVal = ftVal.floatValue();
      dVal = dbVal.doubleValue();

      //String to primitive types
      iVal = Integer.parseInt(str);
      lVal = Long.parseLong(str);
      fVal = Float.parseFloat(str);
      dVal = Double.parseDouble(str);

      //string to wrapper objects
      intVal = Integer.valueOf(str);
      lgVal = Long.valueOf(str);
      ftVal = Float.valueOf(str);
      dbVal = Double.valueOf(str);
  }
}

By the help of Wrapper classes we can convert a primitive
type into Object type . These are the static classes and
provides methods for this .

The wrapper class used for To convert Primitive data Type 
in to User defined data Type and also  Collection class 
contain all user defined data type this user defined data 
type convert into primitive data type