ClassCastException help

Question

Hi
I am building a web application with servlet, JSP using Javabeans, I have created a Created Product and a sub class OrderedProduct
Class Product
Product(name, code, price)
Product(){}
Class OrderedProduct extends Product
OrderedProduct(){}
in the servlet I am trying to cast
Product selectedproduct = new Product(name,code, price);
OrderedProduct neworder = (OrderedProduct)productselected;
and this gives me an error java.lang.ClassCastException
can anyone know why, please help me not to wast my time I have tried it for two days.
Thank you in advance :)

Answer 1

Your question isn't really a JSP question, but I'll see what I can do to help you.
Essentially what you're doing is trying to cast from something general (Product) to something specific (OrderedProduct)
**NOTE** BTW Your code won't compile as it's written here because you have some of the object references wrong. Here's a sample of class casting that may (or may not help you)
public class Vehicle {
     private String name = null ;
     private String type = null ;
     private int crew = 0 ;
public class Airplane extends Vehicle {
     private int wingSurfaces = 0 ;
     private boolean extraAtmospheric = false ;
     public static void main(String[] args) {
          //     Create an instance of a vehicle
          Vehicle v1 = new Vehicle("Generic", "v1", 0) ;
          //     Create an instance of an airplane
          Airplane a1 = new Airplane("Airplane", "a1", 2, 1, false) ;
          //     Create an instance of a vehicle and then cast it as an airplane
          Vehicle v2 = new Vehicle("Generic", "v2", 0) ;
          //Airplane a2 = (Airplane) v2 ; Causes a ClassCastException at compile
          // Create an instance of an airplane and then cast it as a vehicle
          Airplane a3 = new Airplane("Airplane", "a3", 4, 2, false) ;
          Vehicle v3 = (Vehicle) a3 ;
          Airplane a4 = (Airplane) v3 ;
I've left out the constructors and the accessor / mutator methods for brevity. As you can see, the cast from Airplane to Vehicle works just fine, and you can cast it back to an Airplane if you need to. This is very important for some of the storage mechanisms of Java. But when you try to cast from Vehicle to Airplane the compiler complains because you are trying to cast from general to specific.
Hope this helps, your milage may vary.