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);
  }
}